Organic and Physical Chemistry Using Chemical Kinetics. Prospects and Developments

ORGANIC AND PHYSICAL CHEMISTRY USING CHEMICAL KINETICS: PROSPECTS AND DEVELOPMENTS

ORGANIC AND PHYSICAL CHEMISTRY USING CHEMICAL KINETICS: PROSPECTS AND DEVELOPMENTS

Y.G. MEDVEDEVSKIKH ARTUR VALENTE ROBERT A. HOWELL AND

G.E. ZAIKOV EDITORS

Nova Science Publishers, Inc. New York

Copyright © 2007 by Nova Science Publishers, Inc.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Organic and physical chemistry using chemical kinetics : prospects and developments / Y.G. Medvedevskikh ... [et al.], editors. p. cm. Includes bibliographical references and index. ISBN-13: 978-1-60692-749-6 1. Chemical kinetics. 2. Chemistry, Organic. 3. Chemistry, Physical and theoretical. I. Medvedevskikh, Y. G. QD502.O74 2007 541'.394--dc22 2007017506

Published by Nova Science Publishers, Inc.

New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

ix Conformation and Deformation of Linear Macromolecules in Concentrated Solutions and Melts in the Self–Avoiding Random Walks Statistics Yu. G. Medvedevskikh

1

Thermodynamics of Osmotic Pressure of Polymeric Solutions Yu. G. Medvedevskikh, L. I. Bazylyak and G. E. Zaikov

23

Generalization of Data Concerning to the Coal Swelling in Organic Solvents and Their Extraction Using the Linear Multiparametric Equations L. I. Bazylyak, D. V. Bryk, R. G. Makitra, R. Ye. Prystansky and G. E. Zaikov

35

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains: Synthesis, Properties and Application N. Lekishvili, Sh. Samakashvili, G. Lekishvili and G. Zaikov

51

To Question about Influence of Solvent on Interaction Propanethiole by Chlorine Dioxide R. G. Makitra, G. E. Zaikov and I. P. Polyuzhyn

65

Mathematical Modelling of Thermo-Mechanical Destruction of Polypropylene G. M. Danilova-Volkovskaya, E. A. Amineva and B. M. Yazyyev Energy Criterions of Photosynthesis G. А. Коrablev and G. Е. Zaikov

69

73

vi

Contents

Chapter 8

Spatial-Energy Interactions of Free Radicals G. А. Коrablev and G. Е. Zaikov

Chapter 9

Poly(Vinyl Alcohol)[PVA]-Based Polymer Membranes: Synthesis and Applications Silvia Patachia, Artur J. M. Valente, Adina Papancea and Victor M. M. Lobo

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Chapter 15

Chapter 16

Chapter 17

Chapter 18

Chapter 19

89

103

The Research on the Process of Thermo-Mechanical Destruction in Polypropylene G.M. Danilova-Volkovskaya and E. A. Amineva

167

Zinccontaining Polymer - Inorganic Composite as Vulcanization Active Component for Rubbers of General and Special Assignment V .I. Ovcharov, I. A. Kachkurkina, O. V. Okhtina and B. I. Melnikov

173

Formation of Carbon Nanostructures and Spatial-Energy Stabilization Criterion G. А. Korablev and G. E. Zaikov

187

The Structural Treatment of Limiting Conversion Degree for Solid-State Imidization L. Kh. Naphadzokova, G. V. Kozlov and M. A. Tlenkopachev

201

A Solid-State Imidization and Heterogeneity of Reactive Medium L. Kh. Naphadzokova, G. V. Kozlov and G. E. Zaikov

207

Fractal-Like Kinetics of Reesterification Reaction in Catalyst Presence L. Kh. Naphadzokova, G. V. Kozlov and G. E. Zaikov

217

Description of the Model Reesterification Reaction within the Framework of a Strange Diffusion Concept L. Kh. Naphadzokova, G. V. Kozlov and G. E. Zaikov

225

Estimation of Vapor Liquid Equilibrium of Binary Systems Tert-Butanol+2-Ethyl-1-Hexanol and N-Butanol+2-Ethyl-1-Hexanol Using Artificial Neural Network H. Ghanadzadeh and A. K. Haghi Liquid-Liquid Equilibria of the MME (Methylcyclohexane + Methanol + Ethylbenzene ) System H. Ghanadzadeh and A. K.Haghi Sugar Carbamides J. A. Djamanbaev, J. A. Abdurashitova and G. E. Zaikov

233

243 251

Contents Chapter 20

Index

Impact of Chain-End Structure, Basic Comonomer Incorporation and Pendant Structure on the Stability of Vinylidene Chloride Barrier Polymers Bob A. Howell, Adeyinka O. Odelana and Douglas E. Beyer

vii

257

279

PREFACE If it’s green or wiggly, it’s Biology If it’s stinky, it’s Chemistry If it doesn’t work, it’s physics. (Definitions of sciences on the back of Sasha Zaikova’s sweatshirt High School, Perry, Ohio, U.S.A.)

“Inevitability (verity) is something that nobody knows; the truth everybody knows but each has his or her own truth” Proverb

The word truth is a multi-meaning word which can be applied both to science and life. We will not raise social problems but we will go down to the science, particularly chemical science (organic and physical chemistry). We choose chemical kinetics as a method of research because chemical kinetics is a science about chemical processes, mechanisms of reactions, and about possibilities of directing reactions. Parts of the articles in this volume deal with chemical physics, biochemical physics, and physical organic chemistry. All of these fields of science are interconnected with each other. The authors and editors are all part of an international effort to bring these fields of knowledge to readers around the world. All these efforts are collected at symposia to share and exchange knowledge. Symposium is defined as a convivial meeting, usually following a dinner, for drinking and intellectual conversation. It is derived from ancient Greek word sympósion, which means drinking party, and where ancient philosophers gathered to discuss ideas. It is well-known that the ancient Greek philosopher and scientist Plato loved to attend symposiums very much and he even died during a symposium on his birthday, at the age of 81. These are just fun facts on the background of symposia and none of this concerns the authors and editors of this volume. The papers of this volume focus on the different states of modern chemistry (both reviews and original papers.) Editors and authors will be grateful to the readers for valuable remarks that will be taken into account in further work and research. In the U.S.A., in the times of the Wild West, there was a proverb, stating that “A good word is appreciated, but a good word with a gun behind it is even better.” Interpreting and applying this proverb to modern times and situations, one can say that new hypotheses and

x

Y.G. Medvedevskikh, Artur Valente, Robert A. Howell, et al.

ideas are always appreciated, but new hypotheses and ideas with experimental data and other proof behind them are better. In the words of an engineer-mechanic of the Russian aviation, Vitalii K. Petukhov, said “Try your best to do your best, because bad things will happen on their own” We would like to accept this idea, because our dream is good volume for readers. However, the last decision (the volume is good or bed) will be done by our readers. Editors Prof. Yurii G.Medvedevskikh Branch of L.V.Pisarzhevskii Institute of Physical Chemistry National Academy of Sciences L’viv, Ukraine Dr. Artur Valente, Coimbra University Coimbra, Portugal Prof. Bob Howell Central Michigan University Mount Pleasant, Michigan, USA Prof. Gennady Zaikov N.M.Emanuel Institute of Biochemical Physics Russian Academy of Sciences Moscow, Russia

Chapter 1 - It was proposed a strict statistics of self–avoiding random walks in the d– measured lattice and continuous space for intertwining chains in the concentrated solutions and melts. On the basis of this statistics it was described the thermodynamics of conformation and isothermal and adiabatic deformation of intertwining chains. It has been obtained the equation of conformational state. It was shown, that in the field of chains overlap they are stretched increasing its conformational volume. In this volume there are others chains with the formation of m–ball. Free energy of a chain conformation does not depend upon the fact, if the chains intertwined or they are isolated in the m–ball. Mixing entropy is responsible to the chains interweaving in the m–ball. Dependencies of the conformational radius, free energy and conformation pressure on respective concentration of polymeric chains have been determined. Using the thermodynamics of intertwining polymeric chains of m–ball conformational state and also the laws of isotropic media deformation into linear differential form it were obtained the theoretical expressions for elasticity modules (namely, volumetric volume, Young’s module and shift’s module) and for the main tensions appearing at the equilibrium deformation of the m–ball. Poisson’s coefficient is a function only on the Euclidean’s space and for the real 3–dimensional space is equal to 3/8. It was proposed a simple model explaining the tensile strength of the m–ball by the chains intertwining effect and, thereafter by the loss of the mixing entropy, but not by the chemical bonds breaking.

Preface

xi

Calculations of the elastic properties, the main tensions and tensile strength of natural rubber carried out without using the empirical adjusting parameters are in good agreement with the experimental data. Chapter 2 - It was proposed the analysis of osmotic pressure for diluted, semi–diluted and concentrated polymeric solutions based on the taking into account a free energy of macromolecules conformation as a component of their chemical potential. It was shown, that only into diluted solutions a free energy of macromolecules conformation does not contribute into osmotic pressure and it is described by Vant–Goff’s equation. In a case of semi–diluted and concentrated solutions the contribution of the conformative component of chemical potential of macromolecules into osmotic pressure is dominate. Obtained expressions for the osmotic pressure in a cases of semi–diluted and concentrated solutions are more general than proposed ones in the scaling method and self–consistent field method; generally they are in good agreement with the experimental data and don’t contain the empirical constants. It was discussed the especial role of the critical concentration c* of the polymeric chains intertwining. It was shown, that in this point a free energy of the conformation and also osmotic pressure were determined uniquely, whereas for their derivatives upon the macromolecules concentrations the jump is observed. On the basis of these peculiarities the concentration c* is the critical point of the second order phases transition for the polymeric solutions. This in accordance with the de Clause assumes the Scaling’s ratios application near c*, although does not establish the criteria for the indexes of corresponding power functions estimation. Chapter 3 - Approaches to the consideration of a coal swelling process, which were used up to now and based on the theory of regular solutions, do not give the possibility to generalize quantitatively the experimental data. Adequate relation between the physical– chemical properties of the solvents and the degree of a coal swelling in them can be obtained only with the use of linear multiparametric equations which take into account the effects of the all processes proceeding in the system; besides, the basicity and a molar volume of the liquids are determinative. Such approach is effective at the generalization of data concerning to extraction of a coal. Chapter 4 - On the basis of the diallylsilazanes, α,ω-dihydrideoligoorganosiloxanes and 1,4-bis(dimethylhydridesilyl)benzene, new polyfunctional siliconorganic polymers have been synthesized. General regularities and feasible mechanism of the reaction for obtaining diallylsilazanes have been studied. Based on data of elemental, IR and NMR 1H spectral analysis, the composition and structure of synthesized polymers have been established. The kinetics of polyhydrosailylation reactions has been studied. Quantum-chemical calculations of the model system and data of NMR 1H spectra of the real products of the polyaddition reaction have confirmed probability of passing polyhydrosilylation reaction according to the aforementioned two concurrent directions obtaining both α and β adducts. For the evaluation of relative activity for selected monomers the algebraic-chemical approach has been used. Using Differential Scanning Calorimetric and Roentgen-phase analyses methods it has been established that synthesized polymers are amorphous systems. Thermal (phase) transformation temperatures of synthesized polymers have been determined. Thermooxidation stability of the synthesized polymers has been studied. There was shown that their thermooxidation stability exceeded the analogical characteristic of polyorganocarbosiloxanes.

xii

Y.G. Medvedevskikh, Artur Valente, Robert A. Howell, et al.

Using synthesized diallylsilazanes modification of the properties of some important industrial polymer composites based on phenolformaldehide resins has been carried out. Preliminary investigations showed that synthesized polymers in combination with phenolformaldehyde resins were successfully used as binding-components for polymer/graphite and polymer/carbon black electro-conducting composites. Chapter 6 - There has been provided mathematical description of the processes of thermonuclear destruction in deformed polypropylene melts; the aim was to use the criterion of destruction estimation in modelling and optimising the processing of polypropylene into products. Chapter 7 - The application of methodology of spatial-energy interactions (P-parameter) to main stages of photosynthesis is given. Their energy characteristics are calculated. The values obtained correspond to the reference and experimental data. Chapter 8 - Spatial-energy characteristics of many molecules and free radicals are obtained. The possibilities of applying the P-parameter methodology to structural interactions with free radicals and photosynthesis energetics evaluation are discussed. The satisfactory compliance of calculations with experimental and reference data on main photosynthesis stages is shown. Chapter 10 - There has been investigated the effect of thermo-mechanical impact conditions on destruction kinetics in polypropylene melts. The conditions served as a basis for obtaining quantitative dependencies and mathematical expressions aimed at describing destruction processes. Chapter 11 - In work the synthesis technology of zinccontaining polymer - inorganic composite on the basis of products of secondary raw material processing at joint precipitating with carbamide and formaldehyde (ZnCFO) is described. The structure and properties of ZnCFO are investigated by the differencial-thermal analysis, electronic microscopy and IR-spectroscopy. The ZnCFO action as vulcanization active component of elastomeric compositions on the basis of rubbers of general and special assignment with various vulcanization systems is investigated. The comparative estimation of ZnCFO efficiency depending on type of vulcanization system is given. The ZnCFO influence on character of formed morphological structure of rubbers is determined by the method of percalation analysis. Chapter 12 - Spatial-energy criterion of structure stabilization was obtained. The computation results for a hundred binary systems correspond to the experimental data. The basic regularity of organic cyclic compound formation is given and its application for carbon nanostructures is shown. Chapter 13 - It was shown, that limiting conversion (in the given case - imidization) degree is defined by purely structural parameter – macromolecular coil fraction, subjected evolution (transformation) in chemical reaction course. This fraction can be correctly estimated within the framework of fractal analysis. For this purpose were offered two methods of macromolecular coil fractal dimension calculation, which gave coordinated results. Chapter 14 - It was shown, that the conception of reactive medium heterogeneity is connected with free volume representations, that it was to be expected for diffusioncontrolled solid phase reactions. If free volume microvoids were not connected with one

Preface

xiii

another, then medium is heterogeneous, and in case of formation of percolation network of such microvoids – homogeneous. To obtain such definition is possible only within the framework of the fractal free volume conception. Chapter 15 - It was shown, that the reesterification reaction without catalyst can be described by mean-field approximation, whereas introduction of catalyst (tetrabutoxytitanium) is defined by the appearance of its local fluctuations. This effect results to fractal-like kinetics of reesterification reaction. In this case reesterification reaction is considered as recombination reaction and treated within the framework of scaling approaches. Practical aspect of this study is obvious-homogeneous distribution of catalyst in reactive medium or its biased diffusion allows to decrease reaction duration approximately twofold. Chapter 16 - It is shown, that there is principal difference between the description of generally reagents diffusion and the diffusion defining chemical reaction course. The last process is described within the framework of strange (anomalous) diffusion concept and is controled by active (fractal) reaction duration. The exponent α, defining the value of active duration in comparison with real time, is dependent on reagents structure. Chapter 17 - Vapor-liquid equilibrium (VLE) data are important for designing and modeling of process equipments. Since it is not always possible to carry out experiments at all possible temperatures and pressures, generally thermodynamic models based on equations on state are used for estimation of VLE. In this paper, an alternate tool, i.e. the artificial neural network technique has been applied for estimation of VLE for the binary systems viz. tert-butanol+2-ethyl-1-hexanol and n-butanol+2-ethyl-1-hexanol. The temperature range in which these models are valid is 353.2-458.2K at atmospheric pressure. The average absolute deviation for the temperature output was in range 2-3.3% and for the activity coefficient was less than 0.009%. The results were then compared with experimental data. Chapter 18 - The determination region of solubility of methanol with gasoline of high aromatic content was investigated experimentally at temperature of 288.2 K. A type 1 liquidliquid phase diagram was obtained for this ternary system. These results were correlated simultaneously by the UNIQUAC model. By application of this model and the experimental data the values of the interaction parameters between each pair of components in the system were determined. This revealed that the root mean square deviation (RMSD) between the observed and calculated mole percents was 3.57% for methylcyclohexane + methanol + ethylbenzene. The mutual solubility of methylcyclohexane and ethylbenzene was also demostrated by the addition of methanol at 288.2 K. Chapter 19 - The results of experimental researches on the synthesis of sugars derivatives with glycosylamide and thioamide bonds have been presented in this work. The possibility of using their in the preparative chemistry of sugars, some fields of medicine and agriculture has been shown.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 1-21 © 2007 Nova Science Publishers, Inc.

Chapter 1

CONFORMATION AND DEFORMATION OF LINEAR MACROMOLECULES IN CONCENTRATED SOLUTIONS AND MELTS IN THE SELF–AVOIDING RANDOM WALKS STATISTICS Yu. G. Medvedevskikh* Physical Chemistry of Combustible Minerals Department; L. M. Lytvynenko Institute of Physical–Organic Chemistry and Carbon Chemistry; National Academy of Sciences of Ukraine

ABSTRACT It was proposed a strict statistics of self–avoiding random walks in the d–measured lattice and continuous space for intertwining chains in the concentrated solutions and melts. On the basis of this statistics it was described the thermodynamics of conformation and isothermal and adiabatic deformation of intertwining chains. It has been obtained the equation of conformational state. It was shown, that in the field of chains overlap they are stretched increasing its conformational volume. In this volume there are others chains with the formation of m–ball. Free energy of a chain conformation does not depend upon the fact, if the chains intertwined or they are isolated in the m–ball. Mixing entropy is responsible to the chains interweaving in the m–ball. Dependencies of the conformational radius, free energy and conformation pressure on respective concentration of polymeric chains have been determined. Using the thermodynamics of intertwining polymeric chains of m–ball conformational state and also the laws of isotropic media deformation into linear differential form it were obtained the theoretical expressions for elasticity modules (namely, volumetric volume, Young’s module and shift’s module) and for the main tensions appearing at the equilibrium deformation of the m–ball. Poisson’s coefficient is a function only on the Euclidean’s space and for the real 3–dimensional space is equal to 3/8. It was proposed a simple model explaining the tensile strength of the m–ball by the chains intertwining effect and, thereafter by the loss of the mixing entropy, but not by the chemical bonds breaking. Calculations of the elastic properties, *

Yu. G. Medvedevskikh: 3a Naukova Str., 79053, Lviv, UKRAINE; e–mail: [email protected]

2

Yu. G. Medvedevskikh the main tensions and tensile strength of natural rubber carried out without using the empirical adjusting parameters are in good agreement with the experimental data.

Key words: intertwining chains, SARW statistics, conformation, polymer chain, random walks, lattice, thermodynamics, modules of elasticity, forces, work..

1. INTRODUCTION Self–avoiding random walks (SARW) statistics has been proposed [1] for single that is for non–interacting between themselves ideal polymeric chains (free–articulated Kuhn’s chains [2]) into ideal solvents, in which the all–possible configurations of the polymeric chain are energetically equal. From this statistics follows, that under the absence of external forces the conformation of a polymeric chain takes the shape of the Flory ball, the most verisimilar radius Rf of which is described by known expression [3, 4]

R f = aN 3 /( d + 2 )

(1)

Here: a is statistical length of the chain’s link; N is number of the links in chain or its length; d is the dimension of the Euclidean’s space. Polymeric chains in the concentrated solutions and melts at molar–volumetric concentration c of the chains more than critical one c* = (NARfd)-1 are intertwined. As a result, from the author’s point of view [3] the chains are squeezed decreasing their conformational volume. Accordingly to the Flory theorem [4] polymeric chains in the melts behave as the single ones with the size R = aN1/2, which is the root–main quadratic radius in the random walks (RW) Gaussian statistics. SARW statistics leads to other result.

2. SARW STATISTICS FOR INTERTWINING CHAINS IN D–DIMENSIONAL LATTICE SPACE Let us introduce the d–dimensional lattice with the cell’s parameter equal to the statistical length a of the chain’s link; let us notify, that Z is number of cells in a space and m chains are represented in it; every chain has the length N. As same as earlier [1], we will disregard the energetic effects considering the all–possible configurations of the chains as equivalent. We appropriate the random chain and notify as ni the numbers of steps of the end of chain random walk along i–directions of d–dimensional lattice. At this,

∑n

i

=N,

i = 1, d

(2)

i

The probability

ω ( n ) that at given ni the end of chain draws si = ni + − ni − efficient

steps is subordinated to Bernoulli’s distribution [1]

Conformation and Deformation of Linear Macromolecules…

⎛1⎞ ω( N ) = ⎜ ⎟ ⎝2⎠

N

∏ {n ! /[( n + s ) / 2 ]! [( n − s ) / 2 ]!} i

i

i

i

3

(3)

i

Change of a sign si in eq. (3) doesn’t change the value

ω ( n ) ; that is why this probability

represents the probability of fact, that the RW trajectory per ni steps along i–directions of the d–dimensional space will be finished in one of the 2d cells M(s), position data of which are given by vectors s = (si), i = 1, d differing only by the signs of own components si. Condition of the self–avoiding RW trajectories absence on the d–dimensional lattice demands the circumstance at which more than one link of the chain can not be stood in every cell. Links of the chain are inseparable; they cannot be divided one from another and located into the cells in random order. Thereby, number of different methods of mN differing links location per Z identical cells under condition that in every cell more than one link of the chain cannot be stood is equal to Z! / (Z – mN)!. By identify of the cells the antecedent probability of fact that the cell will be occupied by presented link equal to 1/Z, and when will be not occupied – then (1 – 1/Z). Consequently, probability ω ( z ) of mN differing links distribution per Z identical cells is determined by Bernoulli’s distribution

Z! ⎛1⎞ ω( z ) = ⎜ ⎟ ( Z − mN )! ⎝ Z ⎠

mN

⎛ 1⎞ ⎜1 − ⎟ ⎝ Z⎠

Z −mN

(4)

Distribution (3) describes the RW trajectory of one random chain whereas the expression (4) assigns the links distribution of all m chains. That is why, the probability ω ( s ) of common event consisting of the fact that the RW trajectory of random chain is also the SARW trajectory and at given Z, n, N and ni will turned out by its own last step in one among 2d equiprobable cells M(s) will be equal to

ω ( s ) = ( ω ( z ))1 / m ω ( n )

(5)

Using the Stirling’s formula under condition Z >> 1, N >> 1, ni >> 1 and factorizations ln(1–1/Z) ≈ –1/Z, ln(1–mN/Z) ≈ –mN/Z, ln(1±si/ni) ≈ ± si/ni–(si/ni)2/2 accordingly to condition si 1

(69)

The break of m–ball we consider as such equilibrium transition at which m–ball with the intertwining parameter α is divided by the plane of fracture into two m/2–balls with the same intertwining parameter. The entropy of mixing into two m/2–balls will be equal to

αm

ΔSc' = kNαm ln( αm / 2 ) ,

2

>1

(70)

The loss of the entropy of mixing at the m–ball braking will be thereafter the work of a break

Δ( ΔS c ) = ΔSc' − ΔSc ;

ΔFbr = −TΔ( ΔS c ) will be

ΔFbr = kTNαm ln 2

(71)

At breaking the m–ball into two parts it can be assumed that

α = 1 / 2 . Then

ΔFbr = ( 1 / 2 )kTNm ln 2

(72)

This work of the break is created by the work of the m–ball deformation at some critical value of the multiplicity of volumetric deformation Λ vcr . That is why by equating a work of the deformation

ΔFdef accordingly (30) multiplied on m– in calculation per all m–ball at

some critical value

Λv to the work of a break ΔFbr accordingly to (72) we will find Λv : cr

2 ⎤ ⎡ 1 ⎛σ0 ⎞ ⎜⎜ ⎟⎟ N ln 2⎥ Λvcr = ⎢1 + ⎥⎦ ⎢⎣ d + 2 ⎝ Rm ⎠

Knowing the

cr

−1

(73)

Λv , we can calculate the tensile strength Gi at the m–ball stretching cr

cr

along the i–direction.

12. CALCULATIONS AND ILLUSTRATIONS For calculations let us consider the real d = 3–dimensional space assuming that among three main tensions fx, fy and fz only one, for example fz is independent variable, that is external force, and fx, and fy are reaction forces on fz. At the isotropy of m–ball the forces and

Conformation and Deformation of Linear Macromolecules…

17

multiplicities of linear deformations along the x and y axes will be equal: f x = f y , In this case the conformational volume of the m–ball shapes the elongated or strangulated ( f z < 0 , Λz < 1) along z–axis the ellipsoid of rotation.

Λx = Λ y .

( f z > 0, Λz > 1)

For the ellipsoid of rotation the general constraint equations (23) and (46) take on the particular form

2Λv + Λz Λv − 3Λz = 0

(74)

2ψ x + ψ z = 3

(75)

2

2

3

2

By assigning the values

Λz as to singular independent variable the values Λv have been

calculated and further Λx = Λ y = ⎛⎜ Λv ⎞⎟ Λ

1/ 2

⎝

z

⎠

.

For the shortness let us confine to the numerical analysis of the isothermal and adiabatic deformation of natural rubber, which at comparatively low chains cross–linking can be described as a melt. For natural rubber – polyisoprene (C5H8)N – the following parameters have been chosen: number–average molar mass of the chain M = 2·106 g/mole and average length of the chain N = 2,9·104; ρ = 0,91·106 g/m3, a = 0,125 nm. On the basis of these parameters ρ* = 1,54·104 g/m3 and ρ/ρ* = 59,1 were determined. The work of the isothermal deformation in units kT has been calculated in accordance with the equation (30) converted to a form

ΔFdef / kT =

5 1/ 5 ⎛ ρ N ⎜⎜ * 2 ⎝ρ

⎞ ⎟⎟(1 / Λv − 1) ⎠

(76)

Results of the calculations are represented on figure 1. Dependence of ΔFdef / kT for one chain of the natural rubber on

Λz is the same as for

the Flory’s ball [1], but numerically exceeds the last in ρ/ρ* times. Let us notify also, that in spite of the “very much” value ΔFdef / kT for one chain in calculation per one link, this magnitude has an order equal to 1. Temperature change at adiabatic deformation of natural rubber was calculated accordingly to eq. (43) which under assumption cv = cv N , where cv = c p is molar heat 0

0

0

of the isoprene carries to

⎛ ρ ⎞ RT ΔT = 5 2 00 N −4 / 5 ⎜⎜ * ⎟⎟(1 / Λv − 1) cp ⎝ρ ⎠

(77)

where R is universal gaseous constant. At the calculation accordingly to (77) it was assumed in accordance with the reference data for the isoprene cp0 =152,3 J/moleK, T0 = 300 K.

18

Yu. G. Medvedevskikh

(

)

(

Figure 1. The work of the natural rubber deformation at its stretching Λz > 1 and squeezing Λz along z axis. Calculation has been done in accordance with the eq. (76) (see the explanations in text). '

'

)

1) and

squeezing Λz < 1 along z axis. Calculation has been done in accordance with the eq. (77) (see the explanations in text).

Young’s module has been calculated in accordance with the eq. (56) by taking into account (44) and γ = 3 / 8 :

Conformation and Deformation of Linear Macromolecules…

19

2

⎛ ρ kT Y = 3,75 3 N −8 / 5 ⎜⎜ * a ⎝ρ

⎞ 2 2 ⎟⎟ / Λv = Y 0 / Λv ⎠

(78)

where Y0 = 1,97 MPa is Young’s module of non–deformated rubber at T = 300 K. Results of the calculations are represented on figure 3. For the ellipsoid of rotation Gx = Gy, that is why we can write in accordance with the (66)

(

)

(79)

(

)

(80)

⎡1 ⎤ 2 Gx = Y 0 ⎢ 1 / Λv − 1 + I x ⎥ ⎣4 ⎦ ⎡1 ⎤ 2 Gz = Y 0 ⎢ 1 / Λv − 1 + I z ⎥ ⎣4 ⎦

Due to connection (75) every from integrals Ix and Iz can be balanced to one own variable. In accordance with the (67) and (75) we have ψx

(

/5 I x = ∫ dψ x / ψ 13 3 − 2ψ x x

)

2 2/ 5

(81)

1

Iz = 2

ψz 4/ 5

∫ dψ

z

/ψz

9/ 5

(3 −ψ )

2 4/ 5

(82)

z

1

At this, superior limits of the integration are given by the ratios

ψ x = Λx Λv1 / 2 and

ψ z = Λz Λv1 / 2 following from (47). Results of the calculations accordingly to eq. (79) – (82) at Y0 = 1,97 MPa are represented on figure 4. Needed for the estimation of Gzcr value of critical multiplicity of volumetric deformation

Λv was calculated accordingly to eq. (73) by transforming it to a form cr

⎡ 1 ⎛ ρ* Λvcr = ⎢1 + N 4 / 5 ⎜⎜ ⎝ ρ ⎣ 5

⎤ ⎞ ⎟⎟ ln 2⎥ ⎠ ⎦

As a result, we have obtained

−1

(83)

Λv = 0,103 , respectively Λz = 5,39 , Λx = 0,138 . cr

Gzcr = 48 MPa corresponds to these values.

cr

cr

20

Yu. G. Medvedevskikh

150

Y, MPa 100

50

0 0

1

2

3

Λz

4

5

Figure 3. Dependence of the Young’s module on the multiplicity of linear deformation Λz at stretching and squeezing of natural rubber along z axis. Calculation has been done in accordance with the eq. (78) (see the explanations in text).

50

Gz,Gx, MPa Gz

25

Gx

0

Gz -25

Gx -50 0

1

2

3

4

Λz

5

Figure 4. Dependence of the main tensions Gz and Gx on the multiplicity of linear deformation Λz at stretching and squeezing of natural rubber along z axis. Calculation has been done in accordance with the eq. (79) – (82) (see the explanations in text).

As we can see from the figure 4, calculated dependence of the tension Gz on the multiplicity of natural rubber stretch is in good agreement with the experimental data [6, 7,

Conformation and Deformation of Linear Macromolecules…

21

9]. However, the numerical values Gz and Gzcr are in whole rather higher than the experimental ones. It is connected with fact, that the last represent by themselves not faithful, but conventional tensions and tensile strengths, which were estimated with not taking into account the volumetric deformation of the rubber [6, 7, 9].

CONCLUSION Accordingly to the self–avoiding random walks statistics in the field of the chains intertwining that is in concentrated solutions and melts the polymeric chains are stretched increasing its conformational volume. In this volume other chains are also represented forming the m–ball. Free energy of the chain conformation doesn’t depend on a fact if chains are intertwined or they are isolated in m–ball. The entropy of mixing is responsible for the chains intertwining in m–ball, but not free energy of the chains conformation. Dependencies of the conformational radius, free energy and conformation pressure on relative concentration of the polymeric chains into solution or melt have been determined. Thermodynamical analysis of the isothermal and adiabatic deformation of m–ball has been done. Self–avoiding random walks statistics for intertwining polymeric chains and based on it thermodynamics of their conformational state in m–ball permitted to obtain the theoretical expressions for elasticity modules and main tensions appearing at the equilibrium deformation of m–ball. Calculations on the basis of these theoretical expressions without empirical adjusting parameters are in good agreement with the experimental data.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9]

Medvedevskikh Yu. G. // Condensed Matter Physics, 2001, v. 4, № 2 (26), P. P. 209, 219 Kuhn W. Koll. Zs. // 1934, B. 68, S. 2. De Gennes P. G. Scaling Concepts in Polymer Physics // Ithaca: Cornell Univ. Press., 1979. Flory P. J. Statistical Mechanics of Chain Molecules // M.: Myr, 1971. Fedoryuk M. V. Saddle–Point Technique. Moscow, Nauka, 1977, 254 p. (in Russian) Treloar L. The Physics of Rubber Elasticity. Oxford, 1949 Askadskiy A. A. Deformation of Polymers. Moscow, Chimiya, 1973, 448 p. Feynman R., Leighton R., Sands M.. The Feyman Lectures of Physics. // V. 7. Physics of the Continuous Media (Russian translation, Moscow, Mir, 1977), 288 p. Bartenev G. M., Frenkel C. Ya. Physics of Polymers. L.: Chimiya, 1990, 429 p.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 23-33 © 2007 Nova Science Publishers, Inc.

Chapter 2

THERMODYNAMICS OF OSMOTIC PRESSURE OF POLYMERIC SOLUTIONS Yu. G. Medvedevskikh*1, L. I. Bazylyak1 and G. E. Zaikov*2 1

Physical Chemistry of Combustible Minerals Department L. M. Lytvynenko Institute of Physical–Organic Chemistry and Carbon Chemistry; National Academy of Sciences of Ukraine 2 N. Emmanuel Institute of Biochemical Physics Russian Academy of Sciences

ABSTRACT It was proposed the analysis of osmotic pressure for diluted, semi–diluted and concentrated polymeric solutions based on the taking into account a free energy of macromolecules conformation as a component of their chemical potential. It was shown, that only into diluted solutions a free energy of macromolecules conformation does not contribute into osmotic pressure and it is described by Vant–Goff’s equation. In a case of semi–diluted and concentrated solutions the contribution of the conformative component of chemical potential of macromolecules into osmotic pressure is dominate. Obtained expressions for the osmotic pressure in a cases of semi–diluted and concentrated solutions are more general than proposed ones in the scaling method and self–consistent field method; generally they are in good agreement with the experimental data and don’t contain the empirical constants. It was discussed the especial role of the critical concentration c* of the polymeric chains intertwining. It was shown, that in this point a free energy of the conformation and also osmotic pressure were determined uniquely, whereas for their derivatives upon the macromolecules concentrations the jump is observed. On the basis of these peculiarities the concentration c* is the critical point of the second order phases transition for the polymeric solutions. This in accordance with the de Clause assumes the Scaling’s ratios application near c*, although does not establish the criteria for the indexes of corresponding power functions estimation.

* *

Yu. G. Medvedevskikh; L. I. Bazylyak: 3a Naukova Str., 79053, Lviv, UKRAINE; e–mail: [email protected]; G. E. Zaikov: 4 Kosygin Str., 117977, Moscow, RUSSIA; e–mail: [email protected]

24

Yu. G. Medvedevskikh, L. I. Bazylyak and G. E. Zaikov

Key words: osmotic pressure, polymeric solutions, free energy of conformation.

1. INTRODUCTION Osmose plays an essential role in a wide technological and especially in biological systems represented by solutions of biopolymers. That is why understandable is interest of scientists to the problem of osmotic pressure of polymeric solutions which permits comparatively easy experimentally to determine the advantages and deficiencies of theoretical imaginations about thermodynamical properties of polymeric solutions. Two main approaches for osmotic pressure of polymeric solutions theoretical description can be distinguished. First is Flory–Huggins method [1, 2], which afterwards has been determined as method of self–consistent field. In the initial variant the main attention has been paid into pair–wise interaction in the system “gaped monomeric links – molecules of solvent”. Flory–Huggins parameter χ was a measure of above–said pair–wise interaction and this limited application of presented method by field of concentrated solutions. In subsequent variants such method was extended on individual macromolecules into diluted solutions with taken into account the tie–up of chain links by Gaussian statistics [1]. For description of the osmotic pressure π of polymeric solutions the virial decomposition is used in the Flory–Huggins method

π = RT

c⎛ c⎞ ⎜1 + A ⎟ N⎝ N⎠

(1)

in which c is the molar–volumetric concentration of monomeric links; N is the polymerization degree or length of a chain; A is the second virial coefficient which is the main object of analysis of multiple following variants of Flory–Huggins method. It was discovered, that the expression (1) for the description of π into diluted and semi– diluted solutions required of different values of virial coefficient A. In particular, for the estimation of A in a field of diluted solutions it would be better to accept the whole 3

conformation volume of macromolecule as excluded volume, that is RF , and in the field of semi–diluted solutions – the value a (1 − dχ ) [3] where a is a length of a chain link and 3

R f = aN ν

(2)

is the conformation radius of Flory ball with the index ν = 1/2 or 3/5. Further development of the Flory–Huggins method in direction of taking into account the effects of far interaction, swelling of polymeric ball in “good” solvents [4, 5], difference of free volumes of polymer and solvent [6, 7] leaded to complication of expression for virial coefficient A and to growth of number of parameters needed for its numerical estimation, but weakly reflected on the possibility of equation (1) to describe the osmotic pressure of polymeric solutions in a wide range of concentrations. It was admitted that the best variant for the diluted solutions is the Vant–Goff equation

Thermodynamics of Osmotic Pressure of Polymeric Solutions

π RT

=

c N

25

(3)

and for semi–diluted solutions – Fixman equation [8] or Yamakawa equation [9] differing only by the sense of virial coefficient B

π RT

=

c N

⎡ ⎛ c ⎞⎤ ⎢1 + B⎜ c* ⎟⎥ ⎝ ⎠⎦ ⎣

(4)

here c = N / N A RF is critical concentration of monomeric links corresponding to the start 3

*

of the polymeric balls intertwining. From the point of view [3, 10] the main deficiency of the self–consistent field method is fact, that it does not take into account the fluctuative properties of the polymeric solutions and correlations appearing due to the difference of the energies of pair–wise interaction into system monomeric links – solvent tie–up of links into chain. It is considered that these deficiencies somehow are eliminated by Scaling method [3] which is based on the principle of scaled invariance of polymeric solution properties as function of some characteristic parameters, for example length of chain N, relative concentration c/c* and conformation radius RF of Flory ball. Ideology of method conformably to polymer solutions was appeared from the assumption about the analogy of fluctuative behaviour of polymeric chains in semi– diluted solutions and magnetic in external field near the point of change of phase [11]. Analysis of osmotic pressure of semi–diluted polymeric solutions by Scaling method is based [3] on two positions. Accordingly to the first one it is assumed that the polymeric chain is in “good” solvent for which χ < 1 / 2 . This position is necessary in order to index ν in the expression (2) will be determined by the ratio

ν=

3 (d + 2)

(5)

which is correct for swelling ball and gives the value ν = 3/5, but not ν = 1/2 for d = 3– measured space. The second position assumes that in semi–diluted solutions the polymeric chains are as much strong intertwined that the all thermodynamic values, in particular the osmotic pressure, achieve the limit (at N → ∞) depending only on the concentration of monomeric links, but not on the chain length. The following expression is initial for the determination of osmotic pressure of semi– diluted polymeric solutions accordingly to Scaling method:

π RT

=

c ⎛c⎞ f⎜ ⎟ N ⎝ c* ⎠

(6)

26

Yu. G. Medvedevskikh, L. I. Bazylyak and G. E. Zaikov

in which the dimensionless function f(c/c*) has two asymptotics. It is assumed for the diluted solution (c/c* > 1), in which the unknown index m accordingly to the second position of the Scaling method is from independence π on the length of a chain. This leads to the value m = 1/(3ν – 1), that is m = 4/5 for d = 3–dimensional space. That is why the expression (6) is as follow

π RT

= const ⋅ c

or, assuming

π RT

9

4

(7)

ϕ = a 3c as volumetric part of polymer into solution

= const' ⋅ϕ

9

4

(8)

From the point of view [3] the experiments [12] confirm the correctness of the expression (8). However, let note, that the assumption about independence of the osmotic pressure of semi–diluted solutions on the length of a chain is not physically definitely well–founded; per se it is equivalent to position that the system of strongly intertwined chains is thermodynamically equivalent to the system of gaped monomeric links of the same concentration. Therefore, both Flory–Huggins method and Scaling method do not take into account the conformation constituent of free energy of polymeric chains. In presented work the analysis of osmotic pressure of the polymeric solutions has been done with taken into account the thermodynamics of conformation state of macromolecules following from the self–avoiding random walks statistics [13, 14].

2. STARTING POSITIONS The following expression is stringent thermodynamical determination of the osmotic pressure μs

π = − ∫ dμ s / vs

(9)

μs0

in which

μ s 0 and μ s are chemical potentials of the solvent into standard and defined state

respectively and vs its partial–molar volume. It follows from the Gibbs–Durham equation for two–component solution containing ns moles of the solvent and n moles of macromolecules

Thermodynamics of Osmotic Pressure of Polymeric Solutions

dμ s = − where

n dμ ns

27

(10)

μ is the chemical potential of the macromolecules.

Since the polymeric chains unlike to the common molecules possess by free energy of the conformation F (or by negative entropy of conformation which is a measure of polymeric chains self–organization [13]), it should be included as an additional term in usual determination of chemical potential of component of the solution. Hence, we have for the macromolecules

μ = μ 0 + RT ln γc + F

(11)

μ 0 is standard chemical potential of macromolecules; γ is an activity coefficient or

here

coefficient of proportionality between the thermodynamic activity of macromolecules and their molar–volumetric concentration c. Generally, the activity coefficient γ depends on the composition of solution. In the ranges of our narrow purposes of investigations of the macromolecules chemical potential conformation term influence on the osmotic pressure of polymeric solutions we will be neglect by the change of γ lying γ ≅ const in all range of the macromolecules concentrations into solution. This permits to write

dμ = RTd ln c + dF

(12)

Expressions (9) – (12) are initial for analysis of osmotic pressure of macromolecules solution into further presented partial variants.

3. DILUTED SOLUTIONS Let determine the diluted solutions by two conditions

c ≤ c* ,

(13)

ns v s ≅ V

(14)

here:

c* = 1 / N A RF

3

(15)

is critical molar–volumetric concentration of macromolecules into solution corresponding to the start of polymeric chains conformation volumes intertwining; V is general volume of the solution.

28

Yu. G. Medvedevskikh, L. I. Bazylyak and G. E. Zaikov

Accordingly to [13] the conformation radius RF of non–deformated Flory ball is described by the expressions (2) and (5) at d = 3. This dimensionality of real space will be kept further. Free energy F of the conformation in calculation per one mole of macromolecules in general case of diluted solution is equal to [13]

F= here

5 RTN 1 / 5 / λv 2

(16)

λv ≤ 1 is multiplicity of volumetric deformation of Flory ball. In diluted solutions this

multiplicity is function only on the length of a chain and distinction of free energies of the states S1 and S2 of two neighbour monomeric chains. That is why in diluted solutions dF = 0

(17)

It follows that, the determination (9) takes the standard for the diluted solutions form c

n V 0

π = RT ∫ d ln c

(18)

that result (n/V = c) in the Vant–Goff equation

π = RTc

(19)

Hence, in the field of diluted both ideal

(λv = 1) and real (λv < 1) solutions (c ≤ c* ) the

conformation component of the chemical potential of the macromolecules has not an influence on the osmotic pressure, and it is described by Vant–Goff equation.

4. SEMI–DILUTED SOLUTIONS In the given presented case the semi–diluted polymeric solutions determined by the conditions

c ≥ c* ,

(20)

ns v s ≅ V

(21)

The last means that the volumetric part of macromolecules in solution is sufficiently little.

Thermodynamics of Osmotic Pressure of Polymeric Solutions

29

As it follows from [14] in the field of the chains intertwining the molar free energy of the conformation is linear function of relative concentration of macromolecules and is described by the following expression in approximation by deformation of m–ball in real solution

F=

5 ⎛c⎞ RTN 1 / 5 ⎜ * ⎟ 2 ⎝c ⎠

(22)

It follows that

dF =

5 c RTN 1 / 5 d * 2 c

(23)

with taken into account (10), (12), (21) and (23) the determination (9) for osmotic pressure assumes the form c ⎡c n 5 n c⎤ d ln c + N 1 / 5 ∫ d * ⎥ 2 V c ⎦⎥ c* ⎣⎢ 0 V

π = RT ⎢ ∫

(24)

We will obtain after the integration

⎡

⎛ c c* ⎞⎤ − ⎟⎟⎥ , * c ⎠⎦ ⎝c

5 4

π = RTc ⎢1 + N 1 / 5 ⎜⎜ ⎣

c ≥ c*

(25)

The expression (25) is similar to the expression (4) but has more general character: it gives clear and simple determination of virial coefficient B and automatically is transferred into Vant–Goff equation accordingly to condition c = c*. The second term into square brackets (25) points out the relative contribution of the macromolecules conformation free energy into the osmotic pressure. This term is sufficiently

= 4 its part exceeds 80 %. With the c/c* and significant: even at c / c − c / c ≈ 1 and N N increasing this contribution becomes dominant. Accordingly to (19) the osmotic compressibility ∂π / ∂c into diluted solutions does not *

*

1/ 5

depend on the concentration of macromolecules (∂π / ∂c = RT ) ; on the contrary, in semi–

diluted solutions it becomes (as it follows from (25)) as linear function of relative concentration:

c⎞ ⎛ 5 ∂π / ∂c = RT ⎜1 + N 1 / 5 * ⎟ c ⎠ ⎝ 2

(26)

30

Yu. G. Medvedevskikh, L. I. Bazylyak and G. E. Zaikov

5. CONCENTRATED SOLUTIONS Let determine the concentrated polymeric solutions by the conditions

c >> c*

(27)

ns v s < V

(28)

that assumes a great volumetric concentration of macromolecules into solution. Introducing the volumetric part ϕ of macromolecules into solution by the ratio

ϕ = vc

(29)

in which v is partial–molar volume of macromolecules. Attributive expression (9) with taken into account (10), (12) and (23) results in expression (30) by changing the c = ϕ / v ,

c* = ϕ * / v , ns vs = V ( 1 − ϕ ) : ϕ ⎡ ϕ dϕ 5 N 1/ 5 ϕdϕ ⎤ + π = RT ⎢ ∫ ⎥ * ∫ ⎢⎣ 0 v( 1 − ϕ ) 2 ϕ ϕ* v( 1 − ϕ ) ⎥⎦

(30)

In general case v is complicated and independent function on solution composition. However, in narrow purposes of investigations the influence of macromolecules chemical potential conformation component on osmotic pressure we use the approximation v = const . Then after the integration of (30) we will obtain

π =−

RT v

⎡ ⎞⎤ 5 N 1/ 5 ⎛ 1 − ϕ ⎜ ln ( ) 1 ln ϕ − + + ϕ − ϕ * ⎟⎟⎥ , ⎢ * ⎜ * 2 ϕ ⎝ 1−ϕ ⎠⎦ ⎣

ϕ > ϕ*

(31)

It follows that the osmotic compressibility ∂π / ∂c = v∂π / ∂ϕ will be equal to

RT ⎛ 5 1 / 5 ϕ ∂π ⎜1 + N = ϕ* ∂c 1 − ϕ ⎜⎝ 2

⎞ ⎟⎟ , ⎠

ϕ > ϕ*

(32)

Expressions (31) and (32) are more general than the previous ones (25) and (26) and easy transform in them accordingly to condition Taking into account, that

ϕ * ≤ ϕ > 1 . Therefore, under condition ϕ >> ϕ * for concentrated solutions the first additives in (31) and (32) can be neglected and we can obtain

Thermodynamics of Osmotic Pressure of Polymeric Solutions

π =−

5 RT N 1 / 5 [ln(1 − ϕ ) + ϕ ] 2 v ϕ*

31

(33)

∂π 5 N 1/ 5 ϕ = RT * ∂c 2 ϕ 1−ϕ

(34)

This means, that in concentrated solutions π and ∂π / ∂c is wholly determined by the conformation component of chemical potential of macromolecules. Let write other form (33) assigning the condition

ϕ * ≤ ϕ c → c*) or from above (c* < c → c*). On the contrary, the osmotic compressibility in the point c = c* has two values: first is ∂π / ∂c = RT at approach zone c → c* from below, the *

⎛ ⎝

second accordingly to (26) ∂π / ∂c = RT ⎜1 +

5 1/ 5 ⎞ N ⎟ at approach zone c → c* from above. 2 ⎠

The reason of this is the analogous behaviour of free energy of the conformation F and its derivative ∂F / ∂c . In accordance with the (16) and (22) in the point c = c* the value

5 RTN 1/ 5 is uniquely independently on a fact from which side to approach into c*. On 2 the contrary, the derivative ∂F / ∂c in the point c = c* has two values: first is ∂F / ∂c = 0 at 5 1/ 5 * move c → c* from below, the second is ∂F / ∂c = RTN / c at move c → c* from 2 above. Hence, in the point c = c* the derivative ∂F / ∂c has a jump, consequence of which is also the jump of ∂π / ∂c . F=

Since free energy of the conformation F = –TS, where S is the entropy of the conformation, it follows, that at given external parameters P and T neither free energy of conformation F nor it’s the first derivative upon temperature S do not change in the point c = c*, testifying only the hump; but their derivatives upon the concentration test the jump. On the basis of these features the point c = c* is the critical one for the change of phase of the second kind for polymeric solutions. In view of this, the analogy between the magnetic behaviour near the critical temperature of the change of phase and polymeric solution behaviour near the critical concentration c = c* of the change of phase noting by Des Cloizeaux [11] permits to use the scaling correlations, however does not determine the criteria of the corresponding power functions [15] indexes estimation.

Thermodynamics of Osmotic Pressure of Polymeric Solutions

33

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

[15]

Flory P. J. Principles of Polymer Chemistry // New York: Cornell Univ. Press, 1953, 594 p. Huggins M. L. Physical Chemistry of Polymers // New York: Interscience, 1958, 175 p. De Genes Scaling ideas in Physics of Polymers // Moscow: Myr, 1982, 368 p. Zimm B. H., Stockmayer W. H., Fixman M. Excluded Volume in Polymer Chains // J. Chem. Phys., 1953, 21 (10), p. 1716–1723. Zimm B. H., Stockmayer W. H. Dimensions of Chain Molecules Containing Branches and Rings // J. Chem. Phys., 1949, 17 (3), p. 1301–1314. Prigogine I. The Molecular Theory of Solutions // New York: Interscience, 1959, 479 p. Patterson D. Role of Free Volume Changes in Polymer Solutions Thermodynamics // J. Polym. Sci. C, 1968, 16, p. 3379–3389. Fixman M. // J. Chem. Phys., 1960, 33 (2), p. 370–381. Yamakawa H. // J. Chem. Phys., 1965, 43 (4), p. 1334–1344. Grossberg A. Yu., Khokhlov A. R. Statistical Physics of Macromolecules // Moscow: Nauka, 1989, 344 p. Des Cloizeaux // J. Phys. (France), 1976, 37 (5), p. 431–434. Okano K., Wada E., Taru Y., Hiramatsu H. // Rep. Prog. Polym. Sci. Japan, 17, 141 (1974). Medvedevskikh Yu. G. // Condensed Matter Physics, 2001, v. 4, № 2 (26), p. p. 209, 219. Medvedevskikh Yu. G. Conformation and deformation of linear macromolecules in concentrated solutions and melts in the self–avoiding random walks statistics (see paper in presented book) Marck N. H., Parrinello M. Collective Effects in Solids and Liquids // Adam Hilder Ltd, Bristol, 1982.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 35-49 © 2007 Nova Science Publishers, Inc.

Chapter 3

GENERALIZATION OF DATA CONCERNING TO THE COAL SWELLING IN ORGANIC SOLVENTS AND THEIR EXTRACTION USING THE LINEAR MULTIPARAMETRIC EQUATIONS L. I. Bazylyak*1, D. V. Bryk*2, R. G. Makitra2, R. Ye. Prystansky1 and G. E. Zaikov*3 1

Physical Chemistry of Combustible Minerals Department; L. M. Lytvynenko Institute of Physical–Organic Chemistry and Carbon Chemistry; National Academy of Sciences of Ukraine 2 Institute of Geology and Geochemistry of Combustible Minerals; National Academy of Sciences of Ukraine 3 N. Emmanuel Institute of Biochemical Physics; Russian Academy of Sciences

ABSTRACT Approaches to the consideration of a coal swelling process, which were used up to now and based on the theory of regular solutions, do not give the possibility to generalize quantitatively the experimental data. Adequate relation between the physical–chemical properties of the solvents and the degree of a coal swelling in them can be obtained only with the use of linear multiparametric equations which take into account the effects of the all processes proceeding in the system; besides, the basicity and a molar volume of the liquids are determinative. Such approach is effective at the generalization of data concerning to extraction of a coal.

Keywords: swelling.

*

L. I. Bazylyak, R. Ye. Prystansky: 3a Naukova Str., 79053, Lviv, UKRAINE; e–mail: [email protected] D. V. Bryk, R. G. Makitra: 3a Naukova Str., 79053, Lviv, UKRAINE; e–mail: [email protected] * G. E. Zaikov: 4 Kosygin Str., 117977, Moscow, RUSSIA; e–mail: [email protected] *

36

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al.

The action of organic solvents on natural polymers combustible minerals (coal and brown coal or peat) is intensively studied for a long time due to following reasons. Firstly, this is one of the successful method of studying the structure of combustible materials and the second is their technological application for obtaining of a so–called montan–wax or low–molecular liquid extracts which can be transformed into synthetic liquid fuel due to hydration process. Moreover, an interaction of a coal with the solvents is a basis of the coals liquation processes and coals transformation into liquid fuel. The first stage of an interaction in the system “coal–solvent” is a swelling, or an increasing in the volume, as a result of introducing the molecules of a liquid into interstices and directly into the structure of a coal. Depending on the solvent nature and the coal nature, the volume of a coal can increase even in some times, and, respectively the weight growth of investigated sample can be achieved to 100 and more percentages. A review of early works concerning to a coal swelling is represented in [1, 2]. Let us notify, that else in the fifties the coals swelling process was considered as the first degree of their extraction and was connected with physical–chemical interaction of these coals with the solvents [3]. Such process was explained from two points of view, namely: either this process was coursed by adsorption of the liquid into interstices or such process was connected with the change of the cohesion energy of solid and liquid phases of a system. Sanada and co– authors [4 – 6] were taken into account, that the coal is natural three–dimensional polymer and in accordance with the Flory–Huggins’s theory a change of free energy at the coal swelling is conventional sum of the energies of mixing the polymer and solvent and first of all is determined by the disparity of solubility parameters of both components accordingly to Hildebrand parameter δ: ΔG = [ln(1 – Ø2) + χØ22 + Ø2],

(1)

where Ø2 is volumetrical part of netting structure (polymer) in swollen system; and parameter χ indicating the interaction of a polymer with the solvent which is equal to

χ=

β + ( δ 1 − δ 2 )2 V1 RT

(2)

also contains the empirical term β, correction factor, which takes into account the number of branching in the structure of polymer; δ1 and δ2 are Hildebrand’s parameters of solubility for the solvent and polymer and are equal to [(ΔHevapor – RT) / Vm]1/2. After insignificant transformations the Flory–Renner’s equation can be obtained. Such equation helps to calculate the sizes of polymer link between the cross bonds Mc

ρ 2V1Ø21 / 3 , Mc = 2 [ − ln( 1 − Ø2 ) − χØ2 − Ø2 ]

(3)

where ρ2 is the density of a polymer into solution; V1 is molar volume of the solvent. Coefficient χ should be determined empirically for every solvent and, of course, from the concentration dependence of the osmotic pressure and with taken into account a series of

Generalization of Data Concerning to the Coal Swelling…

37

assumptions. In the work Sanada [5] and subsequent works of other authors, the swelling degree in the volumetric parts Q is represented as a function from the δ of solvents. These data in most cases form the parabolic, “belfry”–like curve with a maximum for the solvents, δ2 of which accordingly to a theory of regular solutions is equal to or is near to δ1 of polymer (coal). In reality, it was maintained already in the work [5] that for the coal only approximated dependencies are obtained – a number of experimental data concerning to Q are visibly take one's leaved from the generalizing curve. It was determined in the work [4] at the extraction by solvents in the Soxhlet’s apparatus of vitrain from Yubary field (the content of carbon consists of 85,2 %), that the maximal yields of an extract are observed at their molar volume about 10 cm3/mole (ethylendiamine, dimethylformamide, cyclohexanone 24 – 26 %, acetophenone 35,6 %, pyridine 33,2 %). Such results were explained by the influence of the value of cohesion energy. However, it exists a plenty of exclusions, for example for butanole Vm = 9,5, for which the yield of the extract is only 0,8 %. The explanation of this deviation as a result of the solvent association caused by the presence of hydrogen bond seems unconvincing since under the experiments conditions (the extraction in the Soxhlet’s apparatus, and that is under boiling temperature) the association will be insignificant. It was discovered in the work [6], that the value Mc for japanese coal with the carbon content less than 80 % is unreal low – only 10 (!), next this value is sharply increased and is achieved the maximum Mc = 175 at 85 0C and after that is decreased. Authors starting from following positions explained this fact: firstly, experimental determinations were carried out in pyridine, in which specific interactions can take place and, the second this deviation can be explained by the mistakes at the determination of χ coefficient. The same approach was discussed in the work Kirov and co–authors [7] in detail on example of swelling (and extraction) for three kinds of bituminous Australian coal. These authors confirmed the main observations of Sanada – the swelling degree Q increases from ~ 1,4 in hydrocarbons to ~ 2 in pyridine (δ – 11,0) and again decreases to ~ 1,5 in alcohols. Calculated on this basis value δ of coal increases droningly with increasing the content of carbon from 70 % till 87 % and in a case of more metamorphized coal is sharply decreased again. Data concerning to the extraction of Greta coal are evidence of maximal yield of extract (more than 20 %) under it treatment with ethylendiamine and dimethylformamide (δ – 11,5), however, authors admit a fact that this is a consequence of specific interactions, since in alcohol from the δ of the same order the yield of the extract is only 1 – 2 %. Authors concluded, that although the swelling degree is not directly connected with molecular characteristics of absorbed liquids, however determining factor is their parameter of solubility in spite of the fact that at detailed consideration of the dependencies Q = f(δ) (or f(δ2)) there are a number of deviations (as same as in the work [5]) from the ideal curve for many solvents. It is necessary to notify that although it is hard to estimate the verisimilitude of determined in such a way molecular weights of structural links of a coal between the points of cross bonds, however, in a case of synthetic polymers in a same way determined masses of links visible don’t agree with the values obtained in accordance with others methods. In spite of the indicated lacks, the described above approach is applied to later works concerning to coal swelling and results interpretation. It is necessary to distinguish a plenty of investigations devoted to swelling studies of coal № 6 from Illinois State (standard in USA coal for the carbon–chemical investigations) [8 – 10]. General conclusions are in good agreement with the results of the works [5, 7]. Comparison of swelling degree for different coal in some solvents depending on the content of carbon has been done in the work [11].

38

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al.

Similar investigation for Siberia Kansk–Achynsk coal was carried out in the works [12, 13]. In both cases, as same as in a work [7], it was proved the dependence of swelling degree of coal on the carbon content in it. That is why logically to assume the possibility of specific interactions also during the swelling process, since the values of parameters of the coal solubility δ2, which are determining accordingly to the Flory–Renner’s equation are differed. It depends on fact if the data for all solvents are taking into account in calculations or such calculations are performed with the exclusion of results for solvents able to be as acceptors of hydrogen bonds (amines, ketones). Different results have been obtained also under application of other methods for calculations, especially of the Van–Krevelen’s method [14]. It is notified in the work [15], that the swelling of some coal does not agree with the thesis of regular solutions theory; that is why, it is not allowed to calculate the parameter χ for them. Authors explain this fact by the presence of oxygen atoms in the investigated coal. But also the molecular weight of separate sections (clusters) between the points of crossing for methylated or acetylated samples of this coal is equal only to 300 – 600 in accordance with the calculations (that is unreal). It is necessary to notify, that the critical analysis of the Flory theory application for the determination of molecular mass and the crossing density of the coal structure has been done in the Painter’s works [16]. Authors assert, that the possible formation of hydrogen bonds between the hydroxy groups of low–metamorphized coal has an important role here; that is why, even a lot of empirical amendments introduction into calculations leads to obtaining the understated values of molecular masses of clusters. Taking into account the above–mentioned lacks many authors concluded that the theory of regular solutions is insufficient for adequate description of the coal swelling process (and also for the extraction process) in different solvents since such theory does not take into account the possible specific solvation of active structures of coal and first of all its heteroatoms [17] especially by formation of hydrogen bonds. With the aim of taking into account the possible acid–base interactions it was proposed by Marzec and co–authors [18, 19] to determine the swelling degree as a function of donor number of DN solvents or as a function of their donor and acceptor numbers disparity accordingly to Gutmann. However, corresponding analysis of data concerning to swelling the slessian bituminous coal showed the following: although between the Q and DN is visible symbasis, however the deviations from the straight line is less than for the function Q = f(δ); but, at the same time it is complicated to confirm about the quantitative description of the process. The same conclusion about only qualitative character of such dependence has been done by authors [13] on example of swelling the brown Kansk–Achynsk coal and some kinds of Donbas coal. Above–mentioned facts and disagreements lead to the conclusions [20] that the sorption of solvents by coal is very complicated process, which covers also the changes under the action of solvent into the coal structure and other possible phenomena. That is why, application for a coal the theories developed for the description of thermodynamically equilibrium process of swelling the simple synthetic polymers is unwarranted first of all due to neglect the existing chemical (specific) solvation interactions. As it was confirmed in many investigations, the swelling Flory–Huggins’s model based on the theory of regular solutions is not sufficiently consistent with the real experimental data. It is caused by a range of simplifying assumptions putted into the base of this model and, first of all, the presence of full isoentalpic mixing (solution) of two phases that is in disagreement with the reality – even

Generalization of Data Concerning to the Coal Swelling…

39

in a case of the polymers which do not contain the donor–acceptor groups into the structure a swelling and solution processes are accompanied with a great enthalpy effect; it is know, that even non–specific solvation is often accompanied by the changes of free energy and enthalpy of the system. And isoentalpy will be not remained in a case of the possible donor–acceptor (acid–base) interaction, which is often observed in a case of synthetic polymers with the content of heteroatoms (polyurethane, nitryle rubbers) and is observed in a case of coal as a result of the presence in it such groups as –OH, –COOH, tertiary atom of nitrogen and ect. Calculations on the basis of the theory of regular solutions for the coal swelling have mostly unsatisfactory generalizing and predicted ability. Thus, our main task was to explain the value of coal swelling as an effect of the sum influence of different properties of penetrating liquids and also to obtain the quantitative picture that is possible starting from the principle of the linearity of free energies. The principle of the linearity of free energies (LFE) is applied in chemistry of solutions over 30 years for quantitative description of the solvents influence on the behavior of dissolved substances (spectral characteristics, constants of the reaction rate). In accordance with this principle general change of free energy of the system consists of the separate inter– independent terms and first of all consists of non–specific and specific solvation and also needed energy for the formation of cavity in the structure of liquid phase with the aim of allocation the exterior molecule introducing there. And only full sum of these all possible energetic effects gives the final (equilibrium) energy of the system [21]:

ΔG = ∑ Δg i

(4)

With taken into account, that the constants of the reaction rates are determined via the equilibrium constants of the activated reactive complex formation, and the last in part depend on the solvation processes, it was proposed by Koppell and Palm [22] the following equation in order to determine the influence of medium properties on the reaction rates of processes proceeding in it:

lg K = a0 +

a1 (n 2 − 1) a2 (ε − 1) + + a3 B + a4 ET (n 2 + 2) (2ε + 1)

(5)

This equation takes into account the influence of the polarization f(n2) and polarity f(ε) of the solvents determining their ability to non–specific solvation and also their basicities B [22] which are accordingly to Koppell–Palm’s quantitatively equal to OH–group displacement absorption band in IR–spectrum of the phenol dissolved in given solvent, and electrophilicity accordingly to Reichardt ET characterizing their ability to introduce into acid–base interactions (specific solvation). Appropriateness of this equation for the generalization of experimental data of the dependencies of reactions rates (and also spectral characteristics of dissolved substances) on physical–chemical characteristics of the solvents has been proved by a number of hundred examples. It was determined by us at the attempts to describe the gasses dissolving processes into liquids with the use of the equation (5) that to obtain of satisfactory results the Koppell– Palm’s equation should be expanded by fifth term, which takes into account the density of the

40

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al.

energy of solvents cohesion proportional to the squared Hildebrand’s solubility parameter δ2. Due to this fact necessary energy for the formation of cavity for the allocation of the molecule introducing into liquid phase is taking into account:

lg K = a0 + a1 f (n 2 ) + a2 f (ε ) + a3 B + a4 ET + a5δ 2

(6)

Modified equation was turned out effective for the determination of the solvents influence on the equilibrium of such processes as solubility in different media not only of gases, but solids too, the distribution of substances between two phases, resembling equilibrium processes. So, it will be logically to try to use the equation (6) for the swelling processes. As a matter of fact, it was turned out, that with the use of this equation it is possible to determine the quantitative connection between the properties of the solvents and equilibrium swelling degree of a number of polymers, and also of a coal [23 – 25]. In order to achieve the satisfactorily high values of the coefficients of multiple correlations R, it is necessary to exclude from the calculations the data for some quantity (3 – 5) of the solvents. It is hard to explain it. Besides, it was not quite clear the model of the interactions into the system. In a case when the solvation processes are energetically advantageous (∆G < 0) and that is why promote to the swelling process, that is to the solvent penetration into the structure of polymer, then the role of δ2 factor is remained not clear. Such factor characterizes the energy needed for the cavity formation into the structure of the liquid; at the same time, unlike to the evaporation process, under the swelling of substances into liquid the following process takes place: liquid solvent penetrates into the structure of solid polymeric phase mostly as the whole. At the beginning of ninetieth the works of Aminabhavi are appeared [26]. These worked were concerned the polymeric membranes swelling into organic solvents and to diffusion rate D of the liquids into their structure in which these values were considered as dependencies from the molar volume VM of the liquids. Generalizations obtained in [26] are rather unsatisfactory – approximately linear dependencies lgQ or lgD on VM are observed only in the homologic ranges or in the case of similar solvents. But approach must be considered as logical: it is clear, that in a case of bigger sizes of introducing molecule, the last with difficulty will be penetrated into the structure of polymer including the adsorbent interstice. Low generalizing ability of the dependencies presented in the work [26] can be explained by fact that they do not take into account the solvation effects, which promote to liquids penetration. That is why the equation (6) has been expanded by additional term, which takes into account the influence of molar volume of the solvents:

lg Q = a0 + a1 f ( n 2 ) + a2 f ( ε ) + a3 B + a4 ET + a5δ 2 + a6VM

(7)

Such equation under the stipulation that Q is represented not in the volumetric parts accordingly to the Flory–Huggins’s model but in accordance with the interpretation of equilibrium processes in the chemical thermodynamics as a moles of the solvent absorbed by one gram or by one cm3 of polymer was turn out effective under the generalization of data for swelling degree of different synthetic polymers, for example, polyethylene, in different organic solvents depending on their physical–chemical parameters [27]. That’s why, it was necessary to check the possibility of application the equation (7) for the generalization of data

Generalization of Data Concerning to the Coal Swelling…

41

concerning to coal swelling since this equation takes into account the all important possible energetic effects caused by possible donor–acceptor interaction of active groups of the coal with non–inert solvents including the formation of hydrogen bonds; the effects of non– specific coal solvation with solvents which are caused by a presence in it the cyclic aromatic structures as a result of which the visible influence of the ability of some solvents for the polarization can be expected; and also endothermic effects as a result of steric complications of the solvents penetration (VM) and destruction of the liquid phase structure (δ2). Data concerning to a swelling of the most popular coal (namely, coal Illinois № 6) have been taken by us as a main object of our investigations. This coal is the standard object for the carbon–chemical investigations in USA. These data were already analyzed earlier in works [23 – 25] with the aim of their generalization accordingly to equation (6), but obtained results were unsatisfactory. Evidently this was caused by two factors: i) the influence of the molecules sizes of the solvents penetrating into the coal structure (their molar volume) was not taken into account in these works; ii) analyzed starting values of the swelling degree Q were given accordingly to original works [9 – 11] in ml (sometimes in g) of the solvent absorbed by 1 ml or 1 g of coal since the Flory–Huggins’s model has been used by authors (this model uses the volumes of two liquids which are mutually mixed). If to consider the coal swelling process (and generally polymers swelling processes) as thermodynamically equilibrium process then the free energy change at the penetration and at the absorption of a solvent and, respectively, the equilibrium constant of this process, it is preferable to determine the quantity of connected solvent in molar units. In the presented paper we have checked the efficiency of the above–mentioned factors considering studying the swelling process in organic solvents. Illinois coals are low– metamorphized, bituminous and contain 20 – 31 % of volatile substances, are characterized by ash content 8 – 12 % and sulphur content 4 – 7,8 %. Investigated in the work [8] sample was characterized by following composition: C 79,8; H 5,11; N 1,8; Sorg. 2,0 and O 11,2 %. The samples were pulverized from the soluble components with pyridine; after vacuum– drying they were saturated by solvent’s steams till their full saturation at room temperatures in the closed vessels. Authors give the ratio of the weights for swelled samples respectively to the starting W. Generalization of studied data for 10 solvents in accordance with the fifth– parameter equation (6) leads to the expression with unsatisfactory low value of correlation coefficient R = 0,81 [23]. Exclusion from the consideration the most uncoordinated data for dioxane gives the possibility to obtain the fifth–parameter equation with low, but acceptable degree of connection R = 0,941. At the same time, consideration of the molar volume factor and the change of weight parts on the molar ones essentially improve the correlation – for all 10 studied solvents R = 0,940, and after the exclusion the data concerning to cyclohexane for the rest 9 solvents we obtain the equation with high connection degree R = 0,996 [28]. However, there are only two decisive parameters – the basicity which assists to swelling process and the is molar volume, which opposites to this process; taking into account the needed energy and the negotiation of the cohesion forces have only insignificant influence and the exclusion of this parameter from the calculations practically does not worsen the equation

lg Q = −1,96 + ( 0,665 ± 0 ,074 )10 −3 B − ( 4,12 ± 0,58 )10 −3VM ; R = 0,984 and S = 0,030

(8)

42

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al.

Obtained equations have greater predicted ability comparatively to fifth–parameter equation obtained in the work [23], which does not take into account the factor of molar volume (for nine solvents R is equal to 0,940). The influence of the factor of molar volume is confirmed by fact that between lgQ and VM the neatly marked symbasis is observed, namely: with increasing of VM the value lgQ is decreased. The action of other decisive factor – solvents basicity – is opposite, in other words with the basicity increasing the symbate increasing of lgQ is observed. Evidently, this is caused by the specific solvation of acid centers, which are in the macromolecule of coal and, first of all, of hydroxy groups. Their presence can be assumed taking into account a great number of the oxygen in the Illinois coal. Comparison of these two oppositely directed dependencies leads to the conclusion, that they are mutually compensated. Although these dependencies are only symbate, but the algebraic sum of the influence of these two factors is practically linearly connected with the respective values lgQ [29]. The third factor is more little density of the cohesion energy, which is proportional to needed energy for separation of absorbed molecules from the structure of liquid phase; this factor respectively also decreases the swelling value. However, the influence of this value is insignificant; this fact is confirmed by negligible decreasing of the Q value at its exclusion. The possible processes of non– specific and electrophilic solvation practically do not impact on the value Q. Our considerations about significance of the separate properties of the solvents influence on the swelling degree are confirmed by analogous analysis of data in others works. In the work [10] authors also have been studied the swelling process of the coal Illinois № 6 in the liquid phase. Swelling degree S has been studied by volumetrically as the ratio of volumes of swelling sample to the starting one. Unlike to [8], it was investigated the process in a range of amines including the primary ones, able to the formation of hydrogen bonds and also alcohols. At the generalization of these data in accordance with the fifth–parameter equation without taking into account of VM for the all 17 solvents it was obtained the equation with the low value R = 0,861; but at the use of the sixth parameter equation (7) and after the exclusion of data for isopropanole and dimethylaniline we achieve of high correlation lg Q = −2,91 + ( 0 ,454 ± 1,40 ) f ( n 2 ) + ( 5,73 ± 1,22 ) f ( ε ) + ( 1,43 ± 0 ,37 )10 −3 B − ( 7 ,15 ± 5,26 )10 −3 ET − ( 0 ,722 ± 0,947 )δ 2 − ( 6 ,52 ± 4,54 )10 −3VM

N = 15 , R = 0,981 , S = 0,160

(9)

and after the exclusion of insignificant factors of polarizability and cohesion energy density: lg Q = −2 ,96 + ( 5,67 ± 1,11 ) f ( ε ) + ( 1,5 ± 0 ,30 )10 −3 B − ( 1,47 ± 3,99 )10 −3 ET − ( 4 ,01 ± 2 ,07 )10 −3Vm

R = 0,980 and S = 0,149

(10)

However, the factors of electrophilic solvation and unexpected molar volume have the little influence too. The dependence of lgQ on the solvent property can be satisfactory described by the two–parametric equation too and

Generalization of Data Concerning to the Coal Swelling…

43

lg Q = −4,34 + ( 3,42 ± 0,69 ) f ( ε ) + ( 2,02 ± 0,27 )10 −3 B − ( 0,86 ± 2,55 )10 −3Vm R = 0,968 and S = 0,172

(11)

In this case the basicity and the molar volume of the solvents are decisive factors, the influence of which is oppositely directed. An appearance of the polarity as significant factor is connected with the specific selection of high polar solvents (alcohols, amines). Calculated in accordance with the equation (11) values lgQcalc. and their deviation from the experimental values are represented in Table 1. Accordingly to [9] the swelling process of the Illinois coal № 6 has been carried out principally under other conditions, namely: the samples were previously extracted with pyridine, dried coal was standed till the full saturation with vapors at 100 0C in closed metallic ampoules (with the exception of phenol, investigating temperature of which is 182 0 C). Authors presented the results of investigations as the ratio of swelling W (in percentages) that is the ratio of weights of swelling sample after 1 hour to the dried sample. These data have been previously generalized in the work [24]. Low value R for the all 12 solvents equal to 0,876 after exclusion from the consideration data concerning to the phenol and tetrahydrophurane is increased till 0,972. Essentially better results were obtained with taken into account the molar volume factor. The data concerning to W taken from [9] and calculated on their basis swelling values in moles Q and lgQ are presented in Table 2; the generalization of these data in accordance with the sixth parameter equation (7) leads to higher degree of relationship R = 0,909, and the exclusion from the consideration of one solvent (butylamine) gives the possibility to obtain the equation with satisfactory degree of relationship R = 0,974; an additional exclusion of dimethylformamide gives the equation (11) with R = 0,991. lg Q = −2,61 + (3,50 ± 0,82) f ( n 2 ) + (2,30 ± 0,46) f (ε ) − (0,33 ± 0,14)10 −3 B − (2,37 ± 6,8)10−3 ET + (0,70 ± 0,24)10 −3 δ 2 − (1,5 ± 2,1)10 −3VM

N = 10, R = 0,991 and S = 0,055

(12)

and after the exclusion of insignificant factors lg Q = −2,51 + (2,66 ± 1,20) f ( n 2 ) + (1,80 ± 0,60) f (ε ) − (7,4 ± 5,0)10 −3 ET − (2,8 ± 2,9)10 −3VM

R = 0,964 and S = 0,086

(13)

With the molar volume of the solvents increasing the coal swelling degree is decreased; the same is an effect of the ability to electrophilic solvation. Unlike to both previous cases, the positive influence of the solvents basicity (namely their ability to form the donor–acceptor bonds with acid groups of the coal) here is insignificant evidently as a consequence of especial influence of the conditions of experiment carrying out. Under higher temperatures the hydrogen bonds are easy decomposed. At the same time, the possible positive influence of the factors of non–specific solvation f(n2) and f(ε) is observed. Calculated values lgQ and their discrepancy with the experiment ΔlgQ are presented for the comparison in Table 2.

44

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al. Table 1. Experimental [10] and calculated in accordance with the equation (10) values of swelling degree of the coal Illinois № 6 №

Solvent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

2–Picoline Pyridine Butylamine Propylamine Aniline 2–Hexanone Methylaniline Propanol Ethanol Butanole Methanol Dimethylaniline* Isopropanole* Toluene p–Xylene m–Xylene Benzene

S 2,76 2,75 2,64 2,45 1,99 1,98 1,44 1,36 1,34 1,34 1,23 1,10 1,06 1,06 1,06 1,05 1,04

Experiments Qm103 17,84 21,72 16,57 17,62 10,86 8,120 4,052 4,820 5,824 3,715 5,690 0,789 0,784 0,562 0,487 0,407 0,447

lgQm –1,749 –1,663 –1,781 –1,754 –1,964 –2,090 –2,392 –2,317 –2,235 –2,430 –2,245 –3,103 –3,106 –3,250 –3,312 –3,390 –3,350

Calculations lgQm ΔlgQm –1,794 0,045 –1,808 0,145 –1,941 0,160 –1,655 –0,099 –2,205 0,241 –2,312 0,221 –2,037 –0,355 –2,240 –0,077 –2,194 –0,041 –2,242 –0,188 –2,204 –0,041 –– –– –– –– –3,311 0,061 –3,326 0,013 –3,293 –0,097 –3,362 0,012

Note: *data excluded from the calculations.

Both the equilibrium swelling degree and the kinetics of this process depend on the character of the solvent. In the work [10] it has been studied the swelling rate of the coal Illinois № 6 volumetrically in different solvents; on the starting stages it is ordered to the pseudo–first order reactions kinetics as is observed in the case of polymers swelling too. It helped to determine the respective constants rate of the process, which are presented in Table 3. In the work [25] we have generalized these data for 24 solvents with the use of fifth– parameter equation (6). For the all maximal sequence of the data the value of correlation multiple coefficient R was very low and equal to 0,694 and only after the exclusion from the calculation the data for five solvents (that is practically 20 %) it could obtain the satisfactory value of R = 0,957. Additional taking into account the influence of molar volume, that is transition to sixth parameter equation, gives the possibility to obtain the expression with R = 0,883. And in order to obtain the satisfactory correlation it was enough to exclude from the calculations data for only two solvents, namely 2–hexanone (methylbutyl ketone) and triethylamine lg k = 2,20 − ( 2,55 ± 3,84 ) f ( n 2 ) + ( 1,08 ± 4,26 ) f ( ε ) + ( 4,17 ± 1,12 )10 −3 B − ( 71,7 ± 62,5 )10 −3 ET − ( 0,92 ± 2,45 )δ 2 − ( 42,8 ± 9 ,1 )10−3VM

N = 22, R = 0,959 and S = 0,448

(14)

Generalization of Data Concerning to the Coal Swelling…

45

Table 2. Experimental [9] and calculated in accordance with the equation (12) values of “swelling ratio” of soluble part of coal for the coal Illinois № 6 № 1 2 3 4 5 6 7 8 9 10 11 12

Solvent Dimethylformamide N–Methylpirrolodone Dimethylsulphoxide Ethylendiamine Aniline Butylamine* Pyridine Phenol Pipyridine Tetrahydrofuran Toluene Hexane

Experiments W Qm103 6,2 60,54 5,7 37,17 5,5 49,19 4,6 33,24 4,6 34,13 3,8 29,82 3,7 28,67 3,4 22,49 3,0 19,26 2,8 22,97 2,6 16,65 1,6 6,902

lgQm –1,218 –1,430 –1,308 –1,478 –1,467 –1,525 –1,543 –1,648 –1,543 –1,639 –1,779 –2,161

Calculations lgQm –– –1,503 –1,407 –1,466 –1,513 –– –1,475 –1,512 –1,475 –1,615 –1,874 –2,134

ΔlgQm –– 0,073 0,099 –0,012 0,047 –– –0,068 –0,136 –0,068 –0,024 0,095 –0,027

Note: *data excluded from the calculations.

The equation terms characterizing the influence of non–specific solvation and also cohesion energy have a great standard deviations which are more than the absolute values of the coefficients and that is why are evidently insignificant. Checking the value R decreasing at the exclusion of these terms confirmed this assumption and helped to obtain the equation with lesser quantity of significant terms. This equation also adequately characterizes the influence of the solvents properties on the rate of their penetration into the coal structure; besides, the decisive factor in this case as same as in a case of swelling value is the influence of molar volume of the solvents, increasing of which leads to the process rate decreasing.

lg k = 1,12 + ( 4 ,85 ± 0 ,52 )10 −3 B − ( 66,0 ± 19 ,5 )10 −3 ET − ( 42,1 ± 6,2 )10 −3VM R = 0,957 and S = 0,418 (15) Significant factor as same as in a case of swelling degree is the solvents basicity. With the solvents basicity increasing, the process rate is also increased. The less essential is a role the solvents ability to electrophilic solvation; although this factor increases the process rate but it exclusion from the consideration decreases R till 0,928. The value lgQ calculated in accordance with the equation (15) is represented in Table 3. Decisive role of the VM factor during the adsorption process of the solvents by coal is in agreement with the determined in the work [25] proportionality for the alcohols between lgk and steric factor Es of the Hammet–Taft’s equation.

46

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al. Table 3. Experimental [10] and calculated accordingly to equation (14) values of the logarithms of the constants rate of the coals Illinois № 6 swelling №

Solvent

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Propylamine Butylamine Pyridine 2–Picoline 2–Hexanone∗ Methanol Ethanol Aniline Propanol Butanole Isopropanole Methylaniline Butanole–2 Toluene Isobutanol Dimethylaniline Benzene Pentanol p–Xylene m– Xylene o– Xylene Ethyl benzene Cumene Triethylamine∗

Experiments k105, s–1 1167,0 614,0 316,7 126,7 125,0 53,30 21,30 20,0 10,90 3,84 2,54 2,47 1,32 0,90 0,833 0,59 0,45 0,376 0,375 0,225 0,118 0,113 0,009 0,00038

lgk –1,933 –2,212 –2,499 –2,897 –2,903 –3,273 –3,672 –3,699 –3,963 –4,416 –4,595 –4,607 –4,879 –5,046 –5,079 –5,229 –5,347 –5,425 –5,426 –5,648 –5,928 –5,947 –7,046 –8,420

Calculations lgk –1,679 –2,974 –2,655 –3,124 –– –3,183 –3,624 –3,962 –4,290 –4,926 –4,152 –4,063 –4,694 –5,334 –4,859 –4,578 –4,675 –5,510 –5,924 –5,919 –5,891 –6,032 –6,716 ––

Δlgk –0,254 0,763 0,155 0,226 –– –0,091 –0,048 0,263 0,328 0,511 –0,443 –0,545 –0,185 0,288 –0,220 –0,651 –0,671 0,085 0,498 0,271 –0,037 0,086 –0,330 ––

Note: *data excluded from the calculations.

So, the swelling characteristics of the Illinois coal are determined by total influence of molar volume of liquids and their ability to specific solvation. The same conclusion has been done by authors of the works [30, 31] explaining the adsorption growing by increasing the donor number of the solvents via the formation of hydrogen bond by OH–groups of coal. But these authors have not done respective quantitative generalization giving the possibility on the basis of the linearity of free energies principle adequately to connect the properties of the liquids with their ability to interact with a coal; it was confirmed that the approaches based on the theory of regular solutions equitable only at the consideration of the swelling process in the “inert” (so–called low–basic) solvents, mainly of low–polarity. Correctness of the sixth parameter equation (7) and its simplified forms for the generalization of the swelling data was proved for other coals including the Donbas coal [32] at the parameters B and VM. If to apply the equation (7) to the coal extraction data, then the factor of molar volume VM is insignificant, and the connection between quantities of extracted substance (in g/mole of the solvent) and physical–chemical characteristics can be satisfactorily described by fifth parameter equation (6) or by its simplified forms; in this case possible acid–base interaction is the decisive factor, that is factor B [33 – 35]. This confirmation is in good agreement with the above–said: bigger molecules harder introduce

Generalization of Data Concerning to the Coal Swelling…

47

into the coal structure and after equilibrium state their size does not play the role. Let us notify, that the same approach has the positive results at the data generalization concerning to the solubility of the synthetic low–molecular coal analogous – diphenylolpropane – in 20 solvents. This approach is also applicable for the generalization of data concerning to the coal extraction under sub–critical conditions, but the role of the specific solvation is also insignificant, evidently as a result of its suppression at high temperatures. So, it was discovered the lack of fit the description of the coal swelling process with the use of one–parametric dependencies including those dependencies based on the theory of regular solutions on the solubility parameter of liquids. It was shown, that the quantitative connection between the swelling degree of coal and physical–mechanical properties of the solvents is achieved only on the basis of principle of the linearity of free energy under condition of taking into account the all solvation process. The basicity of the solvents and their molar volume are the factors determining the swelling degree for low–metamorphized coal.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Kibler M. V. Diejstvije rastvoritieliej na ugli // In book: “Khimiya tviordogo topliva” Moscow, 1951. – v. 1. – p. p. 145 – 267. Keller D. V., Smith C. D. Spontaneous fracture of coal // “Fuel” – 1976. – v. 55. – № 4. – p. p. 272 – 280. Kröger K. Die Steinnohleextraction // “Erdöl und Kohle” – 1956. – Bd.9. – H.7. – s. s. 441 – 446. Sanada Y., Honda H. Solvent extraction of coal // Bull. “Chem. Soe. Japan” – 1962. – v. 35. – № 8. – p. p. 1358 – 1360. Sanada Y., Honda H. Equilibrium swelling of coals in various solvents // “Fuel” – 1966. – v. 45. – № 4. – p. p. 451 – 456. Sanada Y., Honda H. Swelling equilibrium of coals by pyridine // “Fuel” – 1966. – ‘v. 45. – № 4. – p. p. 295 – 300. Kirov N. Y., O’Shea J. N., Sergeant G. D. The determination of solubility parameters of coal // “Fuel” – 1967. – v. 47. – p. p. 415 –424. Green T. K., Kovac J., Larsen J. W. A rapid and convenient method for measuring the swelling of coals // “Fuel” – 1984. – v. 63. – № 7. – p. p. 935 – 938. Mayo F. R., Zevely J. S., Pavelka L. A. Extractions and reactions of coals below 100 о C // “Fuel” – 1988. – v. 67. – № 5. – p. p. 595 – 599. Aida T., Fuku K., Fujii M. et al. Steric requirements for the solvent swelling of Illinois № 6 coal // “Energy and Fuels” – 1991. – v. 5. – № 6. – p. p. 74 – 83. Nelson J. F., Mahajant O. T., Walker P. L. Measurement of swelling of coals in organic liquids // “Fuel” – 1980. – v. 59. – № 12. – p. p. 831–837. Skrypchenko G. B., Khrennikova O. V., Rybakov S. I. // “Khimiya tviordogo topliva” – 1987. – v. 5. – p. p. 23 – 28. Osipov A. M., Bojko Z. V. // “Khimiya tviordogo topliva” – 1987. – v. 3. – p. p. 15 – 18.

48

L. I. Bazylyak, D. V. Bryk, R. G. Makitra et al.

[14] Van Krevelen W. Сhemical structure and properties of coal // “Fuel” – 1965. – v. 44. – № 4. – p. p. 229 – 242. [15] Larsen J. W., Shawyer S. Solvent swelling studies // “Energy and Fuels”. – 1990. – v. 4. – № 1. – p. p. 72 – 74. [16] Painter P. C., Graf J., Coleman M. H. Coal solubility and swelling. Parts 1, 2, 3. // “Energy and Fuels” – 1990. – v. 4. – № 4. – p. p. 379 – 397. [17] Weyrich O. R., Larsen J. W. Thermodynamics of hydrogen bonding in coal–derived liquids // “Fuel” – 1983. – v. 62. – № 8. – p. p. 976 – 977. [18] Marzec A., Kisielow W. Mechanism of swelling and extraction and coal structure // “Fuel” – 1983. – v. 62. – № 8. – p. p. 977 – 979. [19] Szeliga J., Marzec A. Swelling of coal in relations to solvent electron–donor numbers // “Fuel” – 1983. – v. 63. – № 10. – p. p. 1229 – 1231. [20] Hsieh S. T., Duda J. L. Probing coal structure with organic vapor sorption // “Fuel” – 1987. – v. 66. – № 2. – p. p. 170 – 178. [21] Mayer U. Eine semiempirische Gleichung zur Beschreibung des Lösungs– mitteleinflusses auf Statik und Kinetik chemischer Reaktionen. Th. 1, 2. // “Monutsh. Chemie” – 1978. – v. 109. – H. 2. – s. s. 421 – 433; H. 4. – s. s. 775 – 790. [22] Koppel I. A., Palm V. A. The influence of the solvent on organic reactivity // In: Advances in Linear Free Energy Relationships. Ed. N. B. Chapman a J. Shorter. London, New York: Plenum Press – 1972. – p. p. 203 – 281. [23] Makitra R. G., Pyrig Ya. M. // “Khimiya tviordogo topliva” – 1988. – v. 6. – p. p. 41 – 45. [24] Makitra R. G., Pyrig Ya. M. // “Khimiya tviordogo topliva” – 1992. – v. 6. – p. p. 11 – 20. [25] Makitra R. G., Pyrig Ya. M., Vasiutyn Ya. M. // “Khimiya tviordogo topliva” – 1995. – v. 3. – p. p. 3 – 13. [26] Aminabhavi T. M., Harogopadd S. B., Khinnavar R. S. et al. Rubber solvent interactions // “Rev. Macromol. Chem. Phys.” – 1991. – v. C 31. – № 4. – p. p. 433 – 497. [27] Makitra R. G., Pyrig Ya. M., Zaglad’ko E. A. // “Plasticheskije massy” – 2001. – v. 3. – p. p. 23 – 27. [28] Makitra R. G., Poliuzhyn I., Prystansky R., Smyrnova O., Rogovyk V., Zaglad’ko O. Zastosuvannya pryncypu linijnosti vilnyh energij shchodo sorbciji ta pronyknennya organichnyh rechovyn // “Praci naukovogo tovarystva im. Shevchenka”. – 2003. – v. 10. – p. p. 152 – 163. [29] Makitra R. G., Prystansky R. // “Khimiya tviordogo topliva” – 2001. – v. 5. – p. 316. [30] Larsen J. W., Green T. K., Kovac J. // “J. Org. Chem.” – 1985. – v. 50. – № 10. – p. p. 4729 – 4735. [31] Hall P. G., Marsh H., Thomas K. M. Solvent induced swelling of coals to study macromolecular structure // “Fuel” – 1988. – v. 67. – № 6. – p. p. 863 – 866. [32] Makitra R. G., Prystansky R. // “Khimiya tviordogo topliva” – 2003. – v. 4. – p. p. 24 – 36. [33] Vasiutyn Ya. M., Makitra R. G., Pyrig Ya. M., Turovsky A. A. // “Khimiya tviordogo topliva” – 1994. – v. 4. – p. p. 66 –73. [34] Makitra R. G., Pyrig Ya. M. // “Khimiya tviordogo topliva” – 1991.– v. 1. – p. p. 67–70.

Generalization of Data Concerning to the Coal Swelling…

49

[35] Makitra R. G., Pyrig Ya. M. // “Khimiya tviordogo topliva” – 1993. – v. 3. – p. p. 14 – 18. [36] Makitra R. G., Bryk S. D., Palchykova O. Ya. Doslidzhennya vzajemodiji malometarmophizovanogo vugillya z organichnymy rozchynnykamy (na prykladi diphenilolpropanu) // “Geologiya i geokhimiya goriuchyh kopalyn”. – 2003. – № 3–4. – p. p. 126 – 130.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 51-64 © 2007 Nova Science Publishers, Inc.

Chapter 4

NEW SILAZANE OLIGOMERS AND POLYMERS WITH ORGANIC-INORGANIC MAIN CHAINS: SYNTHESIS, PROPERTIES AND APPLICATION N. Lekishvili*1, Sh. Samakashvili1, G. Lekishvili1 and G. Zaikov*2 1

I. Javakhishvili Tbilisi State University, Faculty of Exact and Natural Sciences, Scientific Center for Nontraditional Materials; Tbilisi, Georgia 2 N.E. Emanuel Institute of Biochemical Physics of the Academy of Sciences of Russia, Moscow

ABSTRACT On the basis of the diallylsilazanes, α,ω-dihydrideoligoorganosiloxanes and 1,4-bis(dimethylhydridesilyl)benzene, new polyfunctional siliconorganic polymers have been synthesized. General regularities and feasible mechanism of the reaction for obtaining diallylsilazanes have been studied. Based on data of elemental, IR and NMR 1H spectral analysis, the composition and structure of synthesized polymers have been established. The kinetics of polyhydrosailylation reactions has been studied. Quantum-chemical calculations of the model system and data of NMR 1H spectra of the real products of the polyaddition reaction have confirmed probability of passing polyhydrosilylation reaction according to the aforementioned two concurrent directions obtaining both α and β adducts. For the evaluation of relative activity for selected monomers the algebraicchemical approach has been used. Using Differential Scanning Calorimetric and Roentgen-phase analyses methods it has been established that synthesized polymers are amorphous systems. Thermal (phase) transformation temperatures of synthesized polymers have been determined. Thermooxidation stability of the synthesized polymers has been studied. There was shown that their thermooxidation stability exceeded the analogical characteristic of polyorganocarbosiloxanes. Using synthesized diallylsilazanes modification of the properties of some important industrial polymer composites based on phenolformaldehide resins has been carried out. Preliminary investigations showed that synthesized polymers in combination * *

N. Lekishvili: 1, Ilia Chavchavadze ave., 0128 Tbilisi, Georgia, [email protected] G. Zaikov: 119991 Moscow, 5, N.N. Kosigin Street, Russian Federation; [email protected]

52

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al. with phenolformaldehyde resins were successfully used as binding-components for polymer/graphite and polymer/carbon black electro-conducting composites.

Keywords: diallylsilazane, dihydridsiloxane, polyhydrosilylation, properties, application.

INTRODUCTION The synthesis of silicon-organic monomers and polymers (silazane, siloxane-arylene, carbosilazane, epoxide, etc.) containing aromatic groups with unsaturated radicals of allyl and vinyl types have been attracting particular attention [1-4]. The classical method of polyhydrosilylation revealed new possibilities of obtaining polymers with such a structure. The range of unsaturated monomers used for reaction of polyhydrosilylation increased [4-7]. The use of unsaturated monomers of new type, distinguished from the standard divinyl monomers, required elaboration of a non-traditional approach to this reaction [7]. The other hand, the synthesis of polymers with aforementioned structure is of interest for modification of properties of some important industrial polymers, such as polycarbonate, phenolformaldehide resins, rubbers based on organic and siliconorganic elastomers, etc. [7]. They also may be used in combination with some other organic and element-organic polymers (for example, with polyepoxides) as the substrates for nanohybrides [8, 9].

EXPERIMENTAL Synthesis methods: α,ω-oligodihydridedimethylsiloxanes were synthesized by the methods described in ref [11]. 1,3-tetramethyldisiloxane was obtained by hydrolysis of dimethylchlorinesilane [10]. 1,5-trimethyltriphenyltrisiloxane has been synthesized by reduction of 1,5-dichlorine-1,3,5-trimethyltriphenyltrisiloxane with LiAlH4 [10]. 1,5-tetramethyl-3,3-diphenyltrisiloxane was obtained via interaction of (Me)2SiHCl with diphenylsilandiol [7]. Investigation methods: the IR spectra of all samples were obtained, from KBr pellets, on SPECORD and UR-20 spectrophotometers, while NMR 1H spectra were obtained with AM360 instrument at the operating frequency of 360 MHz. All spectra were obtained using CDCl3 as a solvent and an internal standard. Perkin-Elmer DSC-7 differential scanning calorimeter was used to determine DTA and the thermal (phase) transition temperatures were read at the maximum of the endothermic or exothermic peaks. Heating and cooling scanning rates were 100C/min. The column set comprised 103 and 104 Å Ultrastyragel columns. Wideangle X-ray diffractograms were obtained by DRON-2 instrument. Cu Kα was measured without a filter; the motor angular velocity was ω ≈ 20 / min

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

53

RESULTS AND DISCUSSION We have studied polyhydrosilylation reactions of α,ω-oligodiorganodihydride siloxanes and 1,4-bis(dihydridedimetylsilyl)benzene with dialylsilazanes (DAS) in the presence of Speier’s catalyst (0.1 mole solution of H2PtCl6·6H2O in isopropanol) [3-7] in dry toluene and in mass. The initial diallylsilazanes were synthesized via interaction of industrial organocyclosilazanes (hexametylcyclotrisilazane, methylphenylcyclotrisilazane and methylvinylcyclotrisilazane) with orto-allylphenol (o-AP) and 4-allyl-2-methoxyphenol (Evg.), in the area of Argon being free from oxygen and moisture [6]. The reactions proceeded easily in mass, at 333353K, according to the following scheme [6, 7]:

[CH3(R)SiNH]n+2HO-Ar-CH2-CH=CH2

to > − NH 3

, where R = CH3, CH=CH2, C6H5, Ar = phenylene, methoxiphenylene, n=3. Scheme 1.

The resultant products are slightly viscous, optically transparent (in visual area of the spectra) liquids soluble in ordinary organic solvents (benzene, toluene, acetone, etc.) and practically insoluble in water. The composition and structure of the obtained diallylsilazanes were confirmed based on the data of elemental and IR spectral analysis [6, 7] The maximums of the absorption, related to Si−NH−Si and Si−O−Si, Si−O−C groups (915-925 cm-1, 9901000 cm-1 and 1060-1080 cm-1), also the maximums of the absorption, related to Si−CH3, CH2=CH, Si−C6H5 and benzene ring (1250 cm-1, 1430 cm-1, 1445 cm-1, 1620-1630 cm-1, 1600-1605 cm-1 correspondingly) were found in the IR spectra [6]. It should be noted that the method used for manufacturing diallylsilazanes is accessible (easy of access) and has some of noteworthy positive technological features for a practical viewpoint [6]: • • •

The reaction is carried out without (in the absence) solvents and catalysts; Removal of side products is not difficult; Control of the process is simple due to determination of the gaseus ammonia.

Polyhydrosilylation reactions of 1,4-bis(dimethylhydridesillyl)benzene and α,ω-oligodiorganodihydredesiloxanes with sinthesized dilsilazanes are passing according to the following general scheme:

54

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al.

CH 3

(CH 2) 3

R

(CH 2) 3

Si R'

CH 3 Rx

Si R'

n

where Rx= O, C6H4, O[Si(CH3 )2 O]m, (m=6,11), CH3(C6H5)SiO, Si(C6H5)2, R = R1= CH3; R= CH3, R1 = CH=CH2, C6H5; R1 = CH3, C6H5; n>>1. Scheme 2.

Preliminarily we had studied the following model system: (CH3)3SiOSi(CH3)2H + DAS. Heating of the corresponding reaction mixture in the temperature range of 60-80 0C, in the absence of the Speier’s catalyst, showed that the polymerization of DAS or other changes of the structures of the initial compounds do not take place. There didn’t observe any changes in the IR, NMR 1H and NMR 13C of initial compounds. Content of the double bond of the allyl group and active Hydrogen did not change either. The process was controlled by determination of active hydrogen in Si−H groups for several times [2, 6]. The influence of the structure of dihydride monomers on the reaction rate, yield and properties of obtained polymers has been studied (table 1, figure 1). Based on kinetic curves (figure 1) of Si−H groups conversion, the reaction rate constants have been determined (table 1). The total reaction order equals to 2. The products of polyhydrosilylation reaction are optically transparent viscous liquids or elastic gums soluble in ordinary organic solvents (toluene, CHCl3, etc.). The composition and structure of produced polysilazanes were established based on the data of the elemental, IR and NMR 1H spectral analyses. In IR spectra there were found the

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

55

maximums of absorption (915-925 cm-1, 990-1000 cm-1, 1020-1060 cm-1, 1250 cm-1, 1410 cm-1, 1430 cm-1, 1445 cm-1, 1600-1605 cm-1), related to Si−NH−Si, Si−O−Si, Si−O−Car , Si−CH2, Si−CH3, Si−C6H5, and benzene link, correspondingly (scheme 5). The data of elemental analysis (for example, Si(I),%, calc./found.=17.01/16.08; Si(VIII),%, calc./found.=17.84/17.09, etc., where the index numbers I and VIII the numbers of polymers in the table 2) corresponded to the structures of the products, obtained in accordance with the reaction scheme 2. One can observe the singlet signals with chemical shifts within the range of δ ≈ 0.03 _ 0.44 ppm for protons in methyl group of ≡Si−CH3 in NMR 1H spectra of the synthesized polymers (there illustrated the data for IV, V and VI - table 2). One can also observe two signals with the center of chemical shifts at1.28 ppm and 1.62 ppm, which correspond to methylene protons in Si_CH2 groups, and multiplet signals with chemical shifts within the range of δ ≈ 6.6 - 7.5 ppm corresponding to protons of phenyl groups in the NMR 1H spectra. There were observed the signals with chemical shifts within the range of δ ≈ 5.1 _ 5.2 ppm corresponding to protons in NH-groups in NMR 1H spectra. The triplet signals with center of chemical shifts at 0.81 ppm correspond to methine protons in Si_ СH(CH3) _ groups [5].

Figure 1. Conversion of Si−H group in time for hydrosilylation reaction of dihydride siloxanes and 1,4bis(dimethylhydridesilyl)benzene with diallylsilazanes: 1.- VII; 2. - VI; 3.- III; 4.- II; 5.- V; 6.- IV (table 1).

The data given above (elemental and spectral analysis and solubility of the resultant products) excludes homopolymerization of diallylsilazanes under the conditions of polyhydrosilylation reaction. To evaluate relative reactivity of dihydridesiloxanes (determination of the rank of their relative reactivity in polyhydrosilylation reaction), algebraic-chemical method, particularly pseudo-ANB-matrices, has been used for the first time for this type reactions. This method is

56

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al.

a modified version of adjacency matrices [13]. In the context of the aforementioned approach, taking into account the nature (structure) of organic radicals R and R1 at the silicon atoms of the dihydridesiloxanes, it has been established that lg(ΔANB) is efficient topologic index for fixing and investigating QSPR (quantitative structure-property relations) [13]. Corresponding correlation equation has the following form: k=alg(ΔANB)+b , where k is a rate constant for polyhydrosilyation reaction; lg(ΔANB) is a decimal logarithm of the determinant of pseudoANB-matrices; a and b – slope and intercept, which are calculated by method of leastsquares: a=6,792•10-3, b=3,083•10-3. The correlation coefficient r=0.9788 (figure 2).

H

Si

O

Si

H

IV

H

O

Si

Si

O

CH3

C6H5

CH3

CH3

CH3

CH3

Si CH3

The polyaddition reaction rate constants k•10-3, l•mol-1•sec-

12

96.6

0.17

---

333

10

85.5

0.10

2.29

333

12

97.0

0.21

2.78

12

96.4

0.13

4.33

CH3

C6H5

CH3 Si

333

CH3

II

H

ηsp**

CH3

CH3

III

The yield of products of the reactions

dihydridsiloxsanes and 1,4 bis- (dihydridedimethylsillyl)benzine

CH3 I

Reaction temperature,K

#

Duration of reaction, hrs

Table 1. Conditions of hydrosilylation reaction of 1,4-bis(dimethylhydridesillyl)benzine and α,ω-oligodiorganodihydredesiloxanes with diallylsilazanes (DAS)*, the yield and values of specific viscosities of synthesized polymers (in toluene)

O

Si CH3

Si

O 6

H

H

333

CH3

Table 1. (Continued).

Si

H

V

CH3

CH3

CH3 Si

O

C6H5 CH3

H

VII

Si

11

The polyaddition reaction rate constants k•10-3, l•mol-1•sec-

ηsp**

12

91.7

0.22

3.97

333

12

96.2

0.15

2.38

333

12

94.6

0.11

1.54

343

12

93.4

0.12

---

CH3

H

Si

O

Si

333

CH3

C6H5

C6H5 CH3

O

H

Si

O

CH3

Si

H

VI

Si

O

57

CH3

CH3

CH3

The yield of products of the reactions

dihydridsiloxsanes and 1,4 bis- (dihydridedimethylsillyl)benzine

#

Duration of reaction, hrs

Reaction temperature,K

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

H

C8H17 C8H17 CH3 C6H5 CH3 VIII

Si

H

CH3 _

_

O Si C6H5

O Si

H

CH3

_

* CH2=CH CH2 Ar O[(CH3)2SiNH]2(CH3)2SiO_Ar_CH2_ CH=CH2; where Ar= C6H4 (VIII); Ar= CH3OC6H4 (I-VII) (scheme 2); **) 1% solution in toluene.

According to the classic researches, polyhydrosilylation reaction of dihydridesiloxanes with α,ω-divinyloligosiloxanes proceeds according to the general scheme given above (scheme 2) [11]. At the same time, some other modern publications showed that both α and β adducts are obtained (scheme 5) [2-6]. Quantum-chemical calculations of the model system (scheme 5) have confirmed the probability of passing polyhydrosilylation reaction according to mentioned above two concurrent directions.

58

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al.

k10-3 l.mol-1.c-1

4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 4.75

4.8

4.85

4.9

4.95

5

5.1

5.05

Ig(ΔAND) Figure 2. Dependence of value for hydrosilylation reaction rate constants on decimal logarithm of determinant of pseudo-ANB-matrices in the series of α,ω-oligodiorganodihydridesiloxanes (table 1). CH3

CH2

R

Si

CH2 + H

CH

OSi (CH3)3

CH3 CH3 I CH2

CH2

R

CH2

Si

CH3 CH3 II CH2

R

Si

CH3

CH3

CH3

R= CH3O

Si

CH3 Scheme 3.

OSi (CH3)3

CH

CH3 NH

Si

CH3

OSi (CH3)3

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

59

As a method of quantum-chemical calculation, we used AM1 method; MM2 method was applied to perform optimization of geometry of adducts [7]. The calculation of the heat of formation (ΔHform) for the reaction model products showed that formation of α-adduct (I) (ΔHIform = – 1067.77 kJ) is slightly more probable than that of β-adduct (II) (for the product with the structure II, ΔHIIform= – 1055.67 kJ); both I and II products are actually obtained [5]. One can observe the signals with chemical shifts at δ=0.81 and δ=1.62, which correspond to β (II) and α (I) adducts (scheme 4) in NMR 1H spectra of real polysilazanes [5]. In case of the polyhydrosilylation reaction of dihydridesiloxanes with diallylsilazanes (scheme 2) there may also proceed dehydrocondensation reaction (due to the interaction of NH-groups of di- and intermediate oligosilazanes with Si–H groups of dihydridesiloxanes), alongside with the main processes, via obtaining trisilylated nitrogen atom. To determine which process (dehydrocondensation or polyaddition) is more probable, we have calculated basic energetic parameters of model systems, for the products of polyhydrosilylation reaction. As model systems there were selected structures described the actual reaction products [7]:

R'

R'

H3C O

Si H3C

N

Si

CH3

Si

C H2

H C

(III) CH2

CH3

H3C R

,

where R=OCH3, R′=CH3; Scheme 4.

In spite of the fact that formation of model systems containing the trisilylated nitrogen atom is thermodynamically possible (ΔHIIIform.= –928,76 kJ), separation of hydrogen did not take place during the process of polyhydrosylation reaction [6]. At the same time, in IR spectra of actual products of this reaction, the maximum of absorption related to trisilylated nitrogen atoms (950-960cm-1) was not found [6, 7]. Evidently, it is favorable for dihydridesiloxanes to attract terminal allyl groups rather than NH-group bonded to silicon atoms, surrounded with organic radicals under the conditions of polyhydrosilylation reactions. That leads to formation of macromolecules with linear structure (scheme 2) [6]. Using Roentgen-phase (RP) (figures 3) and Differential Scanning Calorimetric (DSC) (figures 4) Analysis Methods, the synthesized polymers have been investigated. It has been established (DSC and RPA methods) that they are amorphous substances. On the DSC-curves (figure 4, a, b and c) endothermic peaks correspond to their glass transition temperature (Tg).

60

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al. 4.55 Å 7.15 Å

7.15 Å

7.08 Å

1

4.31 Å

4.13 Å

2

3

5

10

15

20

25

2Θ°

Figure 3. Difractograms of polymers: 1.-II; 2. IV; 3.-V (table 1).

a HEAT FLOW (mw)

7.5

1 5

2.5

0 -140.0 -110.0 -80.0

-50.0 -20.0

10.0

Temperature

40.0

( 0C)

70.0

100.0 130.0 160.0

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

61

10

b 7.5

5

2.5

0

-140.0 -110.0

-80.0

-50.0

-20.0

10.0

40.0

70.0

100.0

130.0

160.0

Temperature ( 0 C) 10

HEAT FLOW (mw)

c 7.5

5

2.5

0 -140.0 -110.0

-80.0

-50.0

-20.0

10.0

Temperature

40.0

70.0

100.0

130.0

160.0

( 0 C)

Figure 4. DSC corves of polymers: II (a), VI (b), IV (c) (table 1).

Thermooxidation stability of synthesized polymers (DTA and TGA analyses methods, figures 5) exceeds thermooxidation stability of polydimethylcarbosiloxanes containing terminal functional groups [6]. This fact may be explained by formation of intermediate stable cross-linked macromolecules by interaction of N–H group of polysilazanes with H2N–Si groups of linear oligomers [12] at high temperature (210-2300C, in the open air) (figure 3a,

62

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al.

curves of DTA, exothermic pick at the 2200C); these oligomers maybe obtained via hydrolysis of Si–NH–Si bonds by air moisture. Intensive thermooxidation destruction of the synthesized polymers proceeds only within the temperature interval of 350-4500C. Based on the TGA curve (figure 5), calculation of the activation energy (Ea) for the basic process of thermooxidation destruction of synthesized polymers, has confirmed the above mentioned supposition. So the value of calculated Ea (64 kJ/mol) exceeds correspond parameter (52-54 kJ/mol) for polydimethylcarbosiloxanes with terminal functional groups [14].

Figure 5. DTA (a) and TGA (b) corves for polymers X (table 1).

Produced diallyllsilazanes and polymers based on them were used for the modification of the properties of some industrial polymer composites based on polymers with functional groups. Some satisfactory results were also obtained by modification of properties of phenolformaldehyde resin (PFR) composites with the synthesized diallylsilazanes (scheme 1). Thas, addition of diallylsilazanes (1-3 mass %) to this composition has improved some of essential characteristics of hardened PFR (table 3). It should be noted that other important physical and mechanical properties of the composites have remained safe (table 3). Besides the aforementioned, preliminary investigations showed that synthesized oligomers and polymers, in combination with phenolformaldehyde resin, were successfully used as binding component for polymer/graphite electro-conducting composites (ECC) [15, 16]. Obtained ECC were recommended for creation of electrode material for electrolytic section and the chemical (fuel) sources of electrical energy (on the basis of analogous material) [16].

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains…

63

Table 3. Some physical and mechanical properties of the modified phenolformaldehide resin composite

#*

Electrical conductivity, ρ, om.cm

Strength on pressure, σ, MPa

Strength on winding, σ, MPa

I II- 1% III - 1% III - 3%

53,28 49,23 49,63 49,50

21,22 21,22 27,16 56,59

19,80 12,00 18,50 16,90

Specific percussive viscosity, kg. cm/cm2 2,76 2,40 2,45 2,27

IV - 3%

51,67

41,58

26,20

2,75

* I – without modifiers (scheme 1); II – diallylsilazane based on 4-allyl-2-methoxyphenol:hexamethylcyclotrisilazane (2:1); III – diallylsilazane based on 4-allyl-2-methoxyphenol:trimethyltriphenylcyclotrisilazane (2:1); IV – diallylsilazane based on 4-allyl-2-methoxyphenol:hexamethylcyclotetrasilazane (2:1).

ACKNOWLEDGMENT The authors thanks Dr. M. Katsitadze - for the synthesis of 1,3-dimethyl-1,3dioctyledisiloxane and 1,4-bis(dihydridedimetylhyl)benzene, also Prof. Dr. Aneli and Dr. D. Gventsadze - for study of created electro-conducting polymer composites.

REFERENCES [1]

[2]

[3]

[4] [5]

[6]

Silanes and Other Coupling Agents. Edit.: K.I. Mittal. The Fourth International Symposium on Silanes and Other Coupling Agents, MST Conferences, LLC in Orlando, FL, Vol.3. June 11-13, 2003. Kopylov V.M., Koviazina T.G., Buslaeva T.M., Sinicin N.M., Kireev V.V., Gorshkov A.V.. Peculiarity of the Hydrosilylation Reaction of the Polyfunctional Methylvinyland Methylhydrosiloxanes. Zhurnal Obshchei Khimii. (Journal of General Chemistry), 57, 5 1117-1127 (1987) (Rus.); Lekishvili N., Samakashvili Sh., Murachashvili D., Lekishvili G., Gverdtsiteli M.. Oligoepoxysiloxanes with side epoxy groups: synthesis and properties. Chemistry and Industry. (Bulg.). Vol. 77 (2006) (In press). Mukbaniani O.V. and Zaikov G.E. Cyclolinear Organosilicon Copolymers: Synthesis, Properties, Application. Netherlands, Utrecht, VSP (2003). Mukbaniani O., Tatrishvili T., Titvinidze G. Hydrosilylation Reaction of Methylhydridesiloxane to n-Hexene-1. Georgian Chemical Journal. 3, 3 214-215 (2003) (Rus.). Lekishvili N., Samakashvili Sh. Reactions of polyaddition of dihydride siloxanes to diallyl- silazanes: new approaches. Proceedings of Tbilisi State University, 360, 19-23 (2005) (Geo.).

64 [7]

[8] [9]

[10] [11]

[12]

[13] [14]

[15] [16]

N. Lekishvili, Sh. Samakashvili, G. Lekishvili et al. Kopylov V.M., Sokolskaya I.I., Murachashvili D.U., Lekishvili N.G., Khubulava E.I., Zaikov G.E.. New Siliconorganic Modifiers of Rubbers Based on Carbochain Elastomers. Konstruktsii iz Polimernikh Kompozitov, (Constructions from Polymer Composites), 4, 37-48 (2003) (Rus.). Brostow W. The Chain Relaxation Capability. Ch. 5. In performance of Plastics. Ed. W. Brostow, Hanser, Munich-Cincinnati, 2000. Witold Brostow, Wunpen Chonkaew, Haley Hagg and Oscar Olea. V Republican Conference, Chemistry. Abstracts. Georgia, Tbilisi, Georgian Chemical Society. P.41, 2830 October, 2004. Andrianov K.A. Metodi Elementorganicheskogo Sinteza. Kremnii. (Methods of Element Organic Synthesis. Silicon). Mockva, “NAUKA”. 1968 (Rus.). Andrianov K.A., Gavrikova L.A., Rodionova E.F. Investigation of the polyaddition reaction of α,ω-divinylalkyl(aryl)siloxane oligomers with α,ω-dihydroalkyl(aryl)siloxane oligomers. Visokomolekuliarnie soedinenya. (Polymer science) XIII(A), 4 937939 (1971) (Rus.). Lekishvili N.G., Katsitadze M.G., Nakaidze L.I., Khananashvili L.M. Some Kinetically Regularities of Polymerization Condensation Reaction of Organocyclosilazanes with Spacial Groups at Silicon Atoms with Aromatic Dihydroxy compounds. Bulletin of the Academy of Sciences of Georgia. Series of Chemistry. 152, 3 529-531 (1995) (Rus.). Gverdtsiteli M., Gamziani G., Gverdtsiteli I. The Adjacency Matrices of Molecular Graphs and their Modification. Tbilisi University Press. Tbilisi, 1996 (Geo.). N. Lekishvili, M. Kezherashvili, Sh. Samakashvili. Silicon-organic Polymers with Inorganic and Organic-Inorganic Main Chains, Containing Silicon-Nitrogen and Silicon-Oxygen Bonds. Publish Company “UNIVERSALI”. Tbilisi, Georgia, 2006. Aneli J., Khananashvili L., Zaikov G. Structuring and Conductivity of Polymer Composites. Nova Science Publishers, Inc., N.-Y. 1998. Lekishvili N., Gventsadze D., Aneli J., Samakashvili Sh., Khuchua T. Polymer Materials with Specific Properties Based on Secondary Mineral Resources and Petroleum Products. III All-Russian Conference “Physical chemistry of the Processing of Polymers”. Chemical-Technological State University, Ivanovo (Russia), 2006.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 65-67 © 2007 Nova Science Publishers, Inc.

Chapter 5

TO QUESTION ABOUT INFLUENCE OF SOLVENT ON INTERACTION PROPANETHIOLE BY CHLORINE DIOXIDE R. G. Makitra, G. E. Zaikov* and I. P. Polyuzhyn Division of physico-chemistry of fuels of Pisarzhevskij Institute physical chemistry of Ukrainian National Academy of Science , 3A Naukova str., L'viv, Ukraine

The data for influence of solvents on oxidation propanthiole by chlorine dioxide are satisfactorily generalized by means of five parameters equation according to principles of Linear Free Energies Relationships (LFER). An essential role plays the density of media cohesion energy, that bears out radical process nature. Recently the data concerning to interaction of propanthiole with chlorine dioxide in 8 solvents have been published [1]. In this work it was shown, that the dependence of process rate from solvents properties is satisfactory described for seven solvents, after the exclusion of data for ethyl acetate, by the Koppel-Palm four parameters equation (coefficient of multiple correlation R 0,96) at determining role of medium polarity (coefficient of pair correlation between lg(k) and (ε - 1)/(2ε + 1) - r 0.90). Chemical mechanism of the reaction including the formation of ion-radical RS+*Н and radical RS* has been proposed by authors [1]. However, it is known, that in homolytical processes certaine influence on reaction rate has also so-called "cage effect", which is described by density of medium cohesion energy. That was confirmed by generalization of data concerning to influence of solvents upon decomposition rate of benzoyl peroxide [2] or oxidizing processes [3, 4]. That is why the data analysis from work [1] is seemed as expedient by means of five parameter equation:

*

G.E.Zaikov: N.M. Emanuel Institute of Biochemical physics; Russian Academy of Sciences, 4 Kosygin str., Moscow 119991, Russia

66

R. G. Makitra, G. E. Zaikov and I. P. Polyuzhyn

n2 −1 ε −1 + a2 ⋅ + a 3 ⋅ B + a 4 ⋅ ET + a 5 ⋅ δ 2 lg( k ) = a 0 + a1 ⋅ 2 2ε + 1 n +2

(1)

On comparison with known Koppel-Palm equation the equation (1) includes square of Hildebrandt’s solubility parameter δ2 [5], P.219-225. This equation (1) allows with acceptable precision degree to generalize all data from the work [1] (see Table) without necessity of exclusion the data for ethylacetate: lg(k)= 12.57 + (-12.76 ± 9.15)⋅f1(n2) + (23.03 ± 8.02)⋅f2(ε) + (3.72 ± 1.93)⋅10-3⋅B + (-0.67 ± 0.31)⋅ET + (18.04 ± 6.87)⋅10-3⋅δ2 s ± 0.408 N 8 R 0.9638 (2) It is necessary to mark, that as difference to work [1] in presented research for description of electrophilicity more preferable Reichardt parameter (value ET) [2] is applied but not electrophilicity Е offered by Koppel-Palm. As analogy with [1] the exclusion from equation (2) the data for one of solvents - acetone or ethylacetate allows to obtain an equation for lg(k) with R > 0.99. Analysis of meaning for separate parameters of the equation according to [6] by the way of their in turn exclusion shows on only insignificant role of polarizability effects since for the four parameters equation without f1(n2) the correlation coefficient is only insignificantly lesser R 0.9536. The influence of nucleophilic solvation (factor near basicity B in the equation) has relatively low meaning too as at its exclusion value R becomes as 0.9440. In the same time exclusion from the equation any of three rest factors decreases the degree of correlation to not allowed low value R as to 0.919; 0.939; 0.927 relatively. Here the medium polarity has especially significant influence. It is unastonishingly, if one takes into account a high degree of pair correlation between lg(k) and f2(ε) which is equal to 0.901. Values lg(k) calculated by equation (2) are given also in table. In equation (2) significant parameters of "solvation" such as f2(ε) and δ2 have sign "plus". That indicates on preferable solvation of intermediate reactionary complex, which facilitates the reaction runing in result of electrons division. That agrees confirmed with opinion of authors [1] about polar nature of reactive complex. Evidently its formation is limiting stage, because antibatness is observed between lg(k) and ΔG# with high correlation degree as value r is 0.990. Only medium ability to electrophilic solvation ET has a sign "minus", evidently, in consequence of the positive solvation of initial thiol. It is desirable but to note that significant correlation with r 0.916 exists between f2(ε) and ET. Besides, an essential influence is observed of medium cohesion (δ2) since at exclusion of this factor the R value falls to 0.927. That bears out opinion advanced by authors [1] about mainly radical nature of the process. The energetic charactiristics of process such as Е#ACT., ΔН#, ΔG# and ΔS# also can be generalized with acceptable precision by means of five parameters equations. As an example in the table there are given the experimental activation energies (Е#ACT.) and its values calculated by equation (3):

To Question about Influence of Solvent on Interaction Propanethiole…

67

E#АКТ = -51.85 + (-65.14±30.14)⋅f1(n2) + (-125.5±26.4)⋅f2(ε) + (24.90±6.35)⋅10-3⋅B + + (3.70±1.02)⋅ET + (-52.87±22.63)⋅10-3⋅δ2 s ± 1.345 N 8 R 0.9571 (3) Here as well as for lg(k), the exclusion of the most deviating data for one of solvents acetone for ΔG#, heptane or dioxane for Е#ACT and ΔН#, and benzene or heptane for ΔS# allows to receive equations with R > 0.99. For majority of activation descriptors the polarizability as f1(n2) is least meaningful factor exception ΔS# where is δ2 also, as and for lg(k). However its exclusion decreases R from 0.95 to 0.93, that undesirable according to [6]. The exclusion of other parameters from equation is more noticeable. Thus taking into account the cohesion energy density allows essentially to improve upon results of correlation analysis on influence of medium properties on kinetics of oxidation of propanethiole by chlorine dioxide. At the same time a significance of this factor is indirect proof of radical stages in the process. Table. Experimental on [1] and calculated values lg(k) for kinetic of propanthiol oxidation by chlorine dioxide

Solvent

lg(k) experimen t

n-Heptane 1,4- Dioxane Carbon tetrachloride Benzene Diethyl ether Ethylacetate Acetone Acetonitrile

-2.777 -1.444 -1.411 -2.593 -0.086 -1.000 0.583 1.722

computatio n by Eq.(2) -2.773 -1.224 -1.847 -2.353 -0.266 -0.199 0.092 1.689

Е#ACT, ccal/mole experiment computation by Eq. (3) 11.27 11.89 21.00 20.03 6.54 5.14 7.73 9.74 11.54 12.99 13.02 11.91 16.09 15.34 14.74 16.00

REFERENCES [1] [2] [3] [4] [5] [6]

Yakupov M.Z., Lyapina N.K., Shereshovets V.V., Imashev U.B. // Kinetics and catalysis (Rus). 2001. Vol.42. № 5. PP.673-676. Makitra R.G., Pyrih Ya.N.., Havryliv E.M. Depon. In VINITI 1988 № 8418-В-88. Ref. Zh. Khim. 1989. 5Б4128. Kutcher R.V., Vasyutin Ya.M., Makitra R.G., Pyrih Ya.N. // Dokl. Acad. Sci. Ukr.SSR Series "B". 1988. № 6. PP.47-51. Pyrih Ya.N., Makitra R.G., Yatchyshyn Y.Y. // Kinetics and catalysis. (Rus). 1991. Vol.32. № 5. PP.1040-1047. Reichardt Ch. Solvents and Solvent Effects in Organic chemistry. Weinheim: Wiley VCH, 2003. 630 p. Recomendations for Reporting the Results of Correlation Analysis in Chemistry using Regression Analysis // Quant. Struct. Acta Relat. 1985. Vol.4. № 1. P.29.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 69-72 © 2007 Nova Science Publishers, Inc.

Chapter 6

MATHEMATICAL MODELLING OF THERMOMECHANICAL DESTRUCTION OF POLYPROPYLENE G. M. Danilova-Volkovskaya, E. A. Amineva1 and B. M. Yazyyev2 1

Rostov-on-Don Agricultural Machinery State Academy; 344023, Strana Sovetov Street, 1, Rostov-on-Don. e-mail: [email protected] 2 Ushakov Naval State Academy 353900, Lenin Avenue, 93, Novorossiysk

ABSTRACT There has been provided mathematical description of the processes of thermonuclear destruction in deformed polypropylene melts; the aim was to use the criterion of destruction estimation in modelling and optimising the processing of polypropylene into products.

Keywords: Thermo-mechanical destruction, polypropylene, molecular mass, effective viscosity. During processing polypropylene melts under the action of transverse strain there occur strain-chemical conversions which can result in both decrease and increase in their molecular masses; the mechanical effect on the rapidity and level of the occurring processes is considerably more prominent than the mere contribution of thermal and thermal-oxidative breakdown. These data necessitate studying the process of polymer destruction. For this purpose it would be most effective to apply the criterion of assessment of the intensity with which destructive processes happen in polymer melts. If the destruction is observant from the initial value of molecular mass М0 to a certain finite value М∞, then at point of time t the chain group with molecular mass М0 - Мt (where Мt is the average value of molecular mass at a given point of time) is involved in the process. It is natural to assume that the rate of destruction in a unit time is proportional to the whole

70

G. M. Danilova-Volkovskaya, E. A. Amineva and B. M. Yazyyev

number of breakdowns in macromolecules up to the destruction limit. These assumptions enable us to propose an expression for calculating the rate of destruction process:

d (( M t − M ∞ ) / M t = − Kdt (M t − M ∞ ) / M ∞

,

The integration of this expression results in:

ln

Mt − M∞ = − Kt + e , M∞

(1)

Since at t=0 Мt = M0, then:

С = ln

Mt − M∞ M∞

,

(2)

If we substitute (1) with (2) after some transformations we get:

ln

Mt − M∞ = − Kt , M∞

From here:

М t = ( M 0 − M ∞ )e kt + M ∞ ,

As value М0 - М∞ is constant for the polymer of the given molecular mass, we can designate it as A; after substitution we get:

ln

Mt − M∞ = − Kt M0 − M∞

from here:

М t = A ⋅ e − kt + M ∞ ,

where K is the rate constant depending on the

chemical nature of a polymer and, in particular, on how close macromolecular chains are packed. Each criterion obtained from the given expressions represents a concept of one of the interrelated consequences of thermo-mechanical destruction process: decrease in molecular weight, the number of macromolecular breakdowns, and the approach to the possible level of macromolecular destructions. The merit of the criteria is that their values do not depend on the initial molecular weight [1-3].

Mathematical Modelling of Thermo-Mechanical Destruction of Polypropylene

71

Paper 20 dwells on the ideas allowing us to advance in the quantitative assessment of thermo-mechanic destruction degree. Taking these data as a basis we can propose an expression for calculating the degree of thermo-mechanic destruction in the form of:

ϕ а1 =

1 η 0 − kt ⋅ ⋅e , а ηt

(3)

where a is the constant of proportionality which is equal to 3.105. On the other hand:

ϕ а1 = (η а ,τ 1, 2 ,η 0 , it ) ,

(4)

where ηа is the effective viscosity of a material melt, τ1,2 are transverse strains during processing. Combining the defining parameters of equation (3) and modifying this equation into a dimensionless form, it is possible to demonstrate that criterion φ1а, is the function of only two parameters ηа and τ1,2. Comparing (3) and (4) enables the following expression for the criterion of thermomechanic destruction degree to be proposed:

⎛ τ ⋅t ⎞ ϕ а1 = f ⎜⎜η 0 , 1, 2 ⎟⎟ , ηa ⎠ ⎝

(5)

The direct application of this expression in order to estimate the degree of thermomechanic destruction in connection with polymer processing is hindered because the process rate constant depends on the temperature and intensity of thermo-mechanical impact on a material. Consequently, of significant interest is the issue of selecting an attribute for characterizing the degree of destruction. Most researchers consider it worthwhile to simply use viscosity variable (ηа) or characteristic viscosity variable. Here is proposed the criterion for the rate of thermo-mechanical destruction in the polymeric system Ψ11: −τ 12 ⋅t 1 ⎡η 0 ηa ⎤ Ψ = ⋅⎢ е ⎥, a ⎢⎣η a ⎥⎦ 1 1

where τ12 are strain rate tangents.

(6)

72

G. M. Danilova-Volkovskaya, E. A. Amineva and B. M. Yazyyev

This relation is helpful because it provides an opportunity for the quantitative assessment of polymer thermo-mechanical destruction rate in dependence with the thermo-mechanical impact regime during processing. Analyzing the data obtained when testing the samples of extrusion products made of polypropylene, the conducted research on their molecular-weight properties, and the calculated values of the criterion for the destruction processes rate, we concluded that the processes of attachment and bifurcation correspond to the values of Ψ11 = 1, while the processes of destruction correspond to Ψ11= - 1. Assuming that the effective viscosity in a polypropylene melt is sensitive to changes in molecular mass and in chain-length distribution and taking into consideration the specific character of the thermo-mechanical impact developing during extrusion, it is proposed to calculate the intensity of destruction processes from the latter expression. The advantage of the criterion is that it does not require defining the molecular mass of a polymer. Comparing the values of Ψ11, obtained at testing PP samples processed under various technological regimes and calculated with the aid of a mathematical model allows us to propose applying the criterion to the estimation of physical and chemical transformations occurring in a polymer at modifying the parameters of thermo-mechanical impact. Taking into consideration Ψ11 values, we have found the optimal regime when PP is under extrusion processed into products with improved deformation-strength properties [4].

CONCLUSIONS There has been provided mathematical description of the processes of thermonuclear destruction in deformed polypropylene melts; the aim was to use the criterion of destruction estimation in modelling and optimising the processing of polypropylene into products.

REFERENCES [1] [2] [3] [4]

Olroyd J.G. On the formulation of rheological equation of stat. - Trans. Roy. Soc., 1970, A 200, N 1063, p. 523 -527. De Witt T., Mezner .W. A rheological equation of state which predicts non-Newtonian viscosity, normal stresses and dynamics module. J. Appl.Phys., 1985, v. 26, p. 889-892. Baramboymb I.K. Mechanochemistry of high-molecular substances. – 3rd edition. Moscow. The Chemistry publishing house, 1978, p. 34. Danilova-Volkovskaya G.M. The effect of processing parameters and modifiers on the properties of polypropylene and PP-based composite materials. — Doctoral Thesis, (technical sciences). 2005, p. 273.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 73-87 © 2007 Nova Science Publishers, Inc.

Chapter 7

ENERGY CRITERIONS OF PHOTOSYNTHESIS G. А. Коrablev*1 and G. Е. Zaikov*2 1

Basic research-educational center of chemical physics and mesoscopy, Udmurt research center, Ural Division, RAS, Izhevsk 2 Institute of biochemical physics after N.M. Emanuel, RAS, 119991, 4 Kosygina St., Russia, Moscow

ABSTRACT The application of methodology of spatial-energy interactions (P-parameter) to main stages of photosynthesis is given. Their energy characteristics are calculated. The values obtained correspond to the reference and experimental data.

Keywords: Spatial-energy parameter, free radicals, structural interactions, photosynthesis.

DESIGNATIONS m1 and m2 ΔU1 and ΔU2 ΔU Z* n* Wi ri ni SEI Р0 РE *

masses of material points (kg); potential energies of material points (J); their resulting (mutual) potential energy of interaction (J); nucleus effective charge (Cl); effective main quantum number; bond energy of electrons on i-orbital (eV); orbital radius of i-orbital (Å); number of electrons on this orbital; spatial-energy interactions; spatial-energy parameter (eVÅ); effective Р-parameter (eV);

G.А. Коrablev: E-mail: [email protected]

74 R Hv N1, N2, … N РС α ρ PS АТP RuDF PGA NADP PGA Е ЕС (eV).

G. А. Коrablev and G. Е. Zaikov dimensional characteristic of atom or chemical bond (Å); light quantum energy (J, eV); number of homogeneous atoms; average repetition factor in the formula (10); structural Р-parameter of complex structure (eV); coefficient of structural interactions, isomorphism (%); degree of structural interaction (%); photosystem (PSI and PSII); adenosine triphosphate; ribulose-diphosphate; 3 phospho-glycerin acid; nicotine-amide-adenine-dinucleotide-phosphate; phosphor-glycerin aldehyde; energy of bond or molecule reduction (eV); resulting energy of bond or reduction for radical groups

INTRODUCTION Photosynthesis – process of converting electromagnetic energy of the sun rays into the energy of chemical bonds of vital organic substances … [1]. It is the only natural process through which the organic world obtains the reserve of free energy and which provides all bio-organisms with chemical energy. From the moment photosynthesis was discovered by D.M. Priestly (1771-1850), the researches passed several important stages. The first works connected with photosynthesis energy refer to 1850-1900 (R. Mayer, D.G. Stocks, J. Sax). The application of physiological concepts – in 1900-1950 (М.S. Tsvet, А.А. Richter, W. Arnold). Further development of bio-physicochemical aspects of synthesis till now resulted in its modern model and clarified the way of carbon during photosynthesis (M. Calvin), concept of two photosystems (R. Emerson), structure of reaction center (I. Deizinhoffer, H. Michel, R. Huber), etc. The basis of photosynthesis – consecutive chain of redox reactions, during which electrons are transferred from donor-reducer to acceptor-oxidizer with the formation of reduced compounds (carbohydrates) and oxygen isolation. It is known that excitation energy for complex organic molecules of chlorophyll type lasts for 10-8-10-9 sec and can be stored only for insignificant fractions of a second. But during photosynthesis the energy of absorbed light quantum is stored for a long period (from several minutes to millions of years). The energy is stored here in molecular as chemical bonds rich with energy in complex organic structures. Therefore photosynthesis energy can be presented based on the analysis of changes in energies of chemical bonds of molecular structures in dynamics of all main types of photosynthesis. This is the aim to use the methodology of spatial-energy interactions (P-parameter) in this paper.

*

G.Е. Zaikov: E-mail: [email protected]

Energy Criterions of Photosynthesis

75

SPATIAL-ENERGY PARAMETER (Р-PARAMETER) Structural and interatomic interactions are sure to have electron nature. Thus the registration of the extent to which electrons fill the atom valence states is the basis of the method of valence bonds in chemistry and is numerically expressed through coulomb electrostatic interaction. Also important are exchange-promotional structural interactions that determine isomorphism, solubility of components in solid, liquid and molecular media [2]. During the interactions of oppositely charged heterogeneous systems the volume energy of interacting structures is compensated to a certain extent thus leading to the decrease in the resultant volume energy. The analysis of different physical and chemical processes allows assuming that in many cases the principle of adding reciprocals of volume energies or kinetic parameters of interacting structures is executed. Some examples: ambipolar diffusion, total rate of topochemical reaction, change in the light velocity when transiting from vacuum into the given medium, resultant constant of chemical reaction rate (initial product – intermediary activated complex – final product). Lagrange equation for relative movement of isolated system of two interacting material points with masses m1 and m2 in coordinate х can be presented as follows:

1 ΔU

≈

1 ΔU 1

+

1 ΔU 2

(1)

where ∆U1 and ∆U2 – potential energies of material points in elementary section of interactions, ΔU - resulting (mutual) potential energy of these interactions. The atom system is formed from oppositely charged masses of nucleus and electrons. In this system energy characteristics of subsystems are the orbital energy of electrons (Wi) and effective energy of nucleus that takes into consideration the screening effects (by Clementi). Therefore, assuming that the resultant interaction energy of the system orbital-nucleus (responsible for interatomic interactions) can be calculated based on the principle of adding reciprocals of some initial energy components, we substantiate the introduction of Pparameter [2] as an averaged energy characteristic of valence orbitals in accordance with the following equations:

1

1

+

=

1

q r Wn Р 2

i

i

Р

E

=

Р r

0

i

i

(2) E

(3)

G. А. Коrablev and G. Е. Zaikov

76

Р

E

1

Р

=

0

(3а)

R

=

1 2

P0

q

q=

Z* n*

+

1 (Wrn) i

(4)

(5)

Here: Wi – bond energy of electrons [3]; ri – orbital radius of i–orbital [4]; ni – number of electrons of the given orbital, Z* and n* – effective charge of nucleus and effective main quantum number [5], R – numerical characteristic of atom (bond). The Р0 value will be called a spatial-energy parameter, and the РE value – effective Р– parameter. Effective РE–parameter has a physical sense of some averaged energy of valence electrons in atom and is measured in energy units, e.g. in electron-volts (eV). The values of Р0- and РE-parameters of some elements calculated based on equations (25) are given in table 1. Table 1. Р-parameters of atoms calculated via the bond energy of electrons

1

Valence electrons 2

W (eV) 3

ri (Å) 4

q2 0 (eVÅ) 5

Р0 (eVÅ) 6

Н

1S1

13.595

0.5295

14.394

4.7985

2P1

11.792

0.596

35.395

5.8680

2P2

11.792

0.596

35.395

10.061

Atom

С

N

2Р1г 2P3г 2S1 2S2 2S1+2P3г 2S1+2P1г 2S2+2P2 2P1 2P2 2P3 2P4г 2P5г 2S1 2S2 2S2+2P3

19.201

0.620

37.240

15.445

0.4875

52.912

25.724 25.724

0.521 0.521

53.283 53.283

4.4044 13.213 9.0209 14.524 22.234 13.425 24.585 6.5916 11.723 15.830 19.193 21.966 10.709 17.833 33.663

R (Å) 7 0.5295 0.46 0.28 R-I=1.36 0.77 0.69 0.77 0.69

Р0/R (eV) 8 9.0624 10.432 17.137 3.525 7.6208 8.5043 13.066 14.581

0.77 0.77 0.77 0.77 0.77 0.70 0.70 0.70 0.55 0.55 0.70 0.70 0.70

11.715 18.862 28.875 17.435 31.929 9.4166 16.747 22.614 34.896 39.938 15.299 25.476 48.09

Energy Criterions of Photosynthesis

77

Table 1. (Continued) Atom

Valence electrons 2P1 2P1 2P1 2P2

W (eV) 17.195

ri (Å) 0.4135

q2 0 (eVÅ) 71.383

Р0 (eVÅ) 4.663

17.195

0.4135

71.383

11.858

2P4

17.195

0.4135

71.383

20.338

2S1 2S2 2S2+2P4

33.859 33.859

0.450 0.450

72.620 72.620

12.594 21.466 41.804

5.3212

1.690

17.406

5.929 8.8456

O

Ca

S

Se

Р

Mg

4S1 4S2 4S2 4S2 3P1 3P2 3P4 3S1 3S2 3S2+3P4 4P1 4P2 4P2 4P2 4P4 4P4 4S1 4S2 4S2+4P4 4S2+4P4 3P1 3P1 3P3 3P3 3S2 3S2+3P3 3S1 3S2

Mn

4S1 4S2 3d1 4S1+3d1 4S2+3d2 4S2+3d5

Na

3S1

Cl

3P1

11.901 11.901 11.904 23.933 23.933

0.808 0.808 0.808 0.723 0.723

48.108 48.108 48.108 64.852 64.852

6.0143 13.740 21.375 13.659 22.565 43.940 8.5811 15.070 15.070 15.070 24.213

10.963

0.909

61.803

22.787

0.775

85.678

10.659

0.9175

38.199

14.642 25.010 49.214 49.214 7.7864

10.659

0.9175

38.199

16.594

18.951

0.803

50.922

6.8859

1.279

17.501

19.050 35.644 5.8568 8.7787

6.7451

1.278

25.118

17.384

0.3885

177.33

4.9552

1.713

10.058

6.4180 10.223 6.5058 12.924 22.774 38.590 4.6034

13.780

0.7235

59.849

8.5461

R (Å) 0.66 RI=1.36 RI=1.40 0.66 0.59 RI=1.36 RI=1.40 0.66 0.59 0.66 0.66 0.66 0.59 1.97 1.97 R2+=1.00 R2+=1.26 1.04 1.04 1.04 1.04

Р0/R (eV) 9.7979 4.755 4.6188 17.967 20.048 8.7191 8.470 30.815 34.471 19.082 32.524 63.339 70.854 3.0096 4.4902 8.8456 7.0203 7.7061 13.215 20.553 13.134

1.04 1.17 1.17 1.6 1.14 1.17 1.6 1.17 1.17 1.17 1.6 1.10 R3-=1.86 1.10 R3-=1.86 1.10 1.10 1.60 1.60 R2+=1.02

42.250 7.3343 12.880 9.4188 13.219 20.710 15.133 12.515 21.376 42.066 30.759 7.0785 РЭ=4.1862 15.085 8.9215 17.318 32.403 3.6618 5.4867 8.6066

1.30 1.30 1.30 1.30 1.30 1.30 1.89 R+I=1.18 R+I=0.98 1.00 R-I=1.81

4.9369 7.8638 5.0043 9.9414 17.518 29.684 2.4357 3.901 4.6973 8.5461 4.7216

G. А. Коrablev and G. Е. Zaikov

78

Table 1. (Continued) Atom

Fe

К

Valence electrons 4S1 3d1 4S1+3d1 4S2+3d1 4S1

W (eV) 7.0256 17.603

4.0130

ri (Å) 1.227 0.364

2.612

q2 0 (eVÅ) 26.572 199.95

10.993

4S2(*)

Р0 (eVÅ) 6.5089 6.2084 12.717 16.664 4.8490 7.2115

R (Å) 1.26

Р0/R (eV) 4.8325

1.26 1.26 2.36 R+I=1.45 2.36 R+I=1.45

10.093 13.226 2.0547 3.344 3.0557 4.9734

Table 2. Structural РС-parameters calculated via the bond energy of electrons Radicals, fragments of molecules

P i'

ОН

Н2О

СН2 СН3 СН Н3О С2Н5 СН2 СН3 СН3 СН СН СО С=О С=О С-О2 С-О2 СО-ОН CH-OH CO-H

P "i (eV)

PC

17.967 9.7979 9.7979 17.967

10.432 9.0624 10.432 17.138

6.5999 4.7080 5.0525 8.7712

O (2P2) O (2P1) O (2P1) O (2P2)

2·9.0624 2·10.432 2·17.138 28.875 31.929 28.875 31.929 28.875 28.875 31.929 31.929 3·17.138 2·31.929 31.929 28.875 31.929 28.875 31.929 31.929 14.581 17.435 28.875 31.929 12.315 11.152 8.4416

17.967 17.967 17.967 2·17.138 2·17.138 2·9.0624 3·17.138 3·9.0624 17.138 9.0624 17.138 17.967 5·17.138 2·9.0624 3·17.138 3·9.0624 10.432 10.432 20.048 20.048 20.048 2·20.048 2·20.048 8.7712 8.7712 9.0624

9.0226 9.6537 11.788 15.674 16.531 11.125 19.696 14.003 10.755 7.059 11.152 13.314 36.590 11.562 18.491 14.684 7.6634 7.8630 12.315 8.4416 9.3252 16.786 17.774 5.1226 4.9159 4.3705

O (2P2) O (2P2) O (2P2) С (2S12P3г) С (2S22P2) С (2S12P3г) С (2S22P2) С (2S12P3г) С (2S12P3г) С (2S22P2) С (2S22P2) O (2P2) С (2S22P2) С (2S22P2) С (2S22P3г) С (2S22P2) С (2S22P3г) С (2S22P2) С (2S22P2) С (2P2) С (2S12P1г) С (2S12P3г) С (2S22P2) С (2S22P2) С (2S22P2) С (2P2)

(eV)

(eV)

Orbitals

Modifying the rules of adding reciprocals of energy characteristics of subsystems as applied to complex structures we can obtain [6] the equation for calculating РС-parameters of complex structure:

Energy Criterions of Photosynthesis

1 Р

⎛ 1 ⎞ ⎛ 1 ⎞ ⎟ +⎜ ⎟ ⎝ NP E ⎠ ⎝ NP E ⎠

=⎜ С

1

+ ...

79

(6)

2

where N1 and N2 – number of homogeneous atoms in subsystems. The calculation results of some complex structures based on equation (6) are given in table 2. The calculations for 21 elements showed that the values of РE-parameters are similar to corresponding values of total energy of valence electrons according to the statistic model of atom. Simple dependence between PE-parameter and electron density at the distance ri can be obtained (according to the statistic model of atom):

β

2/3 i

= A ⋅ P 0 = A Р E , where А-constant

r

(7)

i

When the solution is formed in the places of atom-components contact, the unified electron density has to be established. The dissolving process is accompanied by the redistribution of this density between valence areas of both particles and transition of some electrons from external spheres to the neighboring ones. It is obvious that if electron densities in free atom-components of the solution at the distances of orbital radius ri are similar, the transition processes between boundary atoms of particles are minimal thus favoring the solution formation. Thus the task of evaluating the solubility in many cases comes to comparative evaluation of electron density of valence electrons in free atoms (on averaged orbitals) participating in the solution formation. In this regard the maximum total solubility evaluated through the coefficient of structural interaction and isomorphism α are determined by the state of minimal value that represent relative difference of effective energies of external orbital:

α=

P'o / ri '− P''o / ri '' 100% ; ( P'o / ri '+ P''o / ri '') / 2

' − " α = РС РС 200% ' + Р" РС С

(8)

(9)

Multiple calculations and comparisons with the experiment allowed arranging the unified averaged figure-nomogram of degree of structural interaction and solubility (ρ) dependence upon coefficient α [2].

80

G. А. Коrablev and G. Е. Zaikov

The following spatial-energy principles defining the character of structural spatial-energy interactions were determined: 1. Complete (total-lot) isomorphic interaction takes place at relative difference of Pparameters of valence orbitals of interchanging atoms (within 4-6%). 2. Р-parameter of the smallest value defines the orbital that is mainly responsible for isomorphism. 3. Qualitatively the isomorphism character is defined by geometrical similarity of orbital shapes responsible for isomorphism. At the same time, the more similar are the extensions, trajectories and inclination angles of such orbitals, the more perfect is isomorphism. According to the degree of isomorphic similarity of interchanging structures they can be classified into three types (I, II, III) given for some cases in table 3.

PHOTOSYNTHESIS. INITIAL STAGE Magnesium atom that is four-coordinated with nitrogen atoms is included into chlorophyll in the central cavity of the whole structure. The porphinated chlorophyll ring is located in aqueous medium. Each central Mg atom forming chelate compound has two bonds by donor-acceptor mechanism and two covalence bonds. Two molecules of bacteriochlorophyll are located close to each other (about 3 Å) and form competent-structure – dimer chlorophyll. In the dynamics of structural permutations all four bonds of each Mg atom become equivalent [7]. All this allows assuming that total effective РE-parameter of Mg will be approximately two times greater than from 2S2-orbital (5.4867х2=10.973 eV). At the first stage of photosynthesis in the system of PS-2 dimensional characteristics of hydrogen atom can change in structured water molecules under the radiation with energy hν from boron radius (0.529 Å) to atomic (“metal”) – 0.46 Å, this corresponds to the obtaining of РE-parameter equal 10.432 eV by hydrogen that is similar to РE-parameter of 2Mg. It should be pointed out that general change in the scale of photosynthesis potentials PS-2 approximately equals 1.5 eV, and the difference between the data of Р-parameters of hydrogen atoms equals 1.37 eV. The rest of hydrogen atoms with “boron” РE-parameter equaled to 9.0624 eV have similar values with РE-parameters of 2Р1-orbitals of nitrogen atoms surrounding magnesium. Other data are not less important: initial value of РE-parameter of 2S2-orbital of magnesium atom gives from РE-parameter (table 3) of radical (О-Н) α=8.24 % and ρ ≈ 77-82 %. This ρ value can increase to even 100 % under the light action due to minor changes in dimensional characteristics of atoms-components. Absolute difference of these Р-parameters equals 0.43 eV, thus corresponding to the changes in the scale of potentials during the synthesis of АТP. Total spatial-energy action upon the bond Н-О-Н of magnesium and nitrogen atoms (table 3) results in the possibility of breaking this bond with the isolation of free hydrogen and oxygen atoms.

Table 3. Photosynthesis structural interactions Atoms .molecules. radicals O-P O-P Mg2+-H H2O-CH2 C-O CO-OH CO-H2O CH2-CO2 2Mg-H Mn-H Mn-O Mn-O N-H Mn-OH Mg-(O-H) K+-H Fe-S Na+-H

1 component Orbitals 2Р2 2Р1 3S2 1S1-2Р2 2S1-2Р1 2Р2-2Р2 2S12Р1г-2Р2 2S22Р2-1S1 3S2 (3S2)* 4S13d1 4S13d1 4S23d2 2Р1 4S1 2S2 4S1 4S23d1 3S1

РE. РС (eV) 8.470* 4.6188* 8.6066 11.788 17.435 8.4416 9.3252 16.531 10.973 9.9414 9.9414 17.518 9.4166 4.3969 5.4867 3.344 13.226 3.901

2 component Orbitals 3Р3 3Р1 1S1 2S12P3г-1S1 2Р2 2Р2 -1S1 1S1-2Р2 2S12P3г-2Р2 1S1 1S1 2P1 2P2 1S1 2P1-2S1 2P1-2S1 1S1 2P2 1S1

РE. РС (eV) 8.9215* 4.1862* 9.0624 11.125 17.967 8.7712 9.0226 16.785 10.432 10.432 9.7979 17.967 9.0624 4.7080 5.0575 3.525 13.215 3.525

α (%)

ρ (mol%)

SEI types

5.19 9.83 5.16 5.79 3.01 7.51 2.21 1.53 5.05 4.82 1.45 2.53 3.83 4.75 8.24 5.27 0.08 10.1

100 60-65 100 100 100 90-95 100 100 100 100 100 100 100 100 77-82 100 100 55-60

I I I II I II II, III III I I II II II II, III II I II I

G. А. Коrablev and G. Е. Zaikov

82

This initial process finishes with the participation of manganese-containing system connected with proteins of reaction center PS-2. Structural reconstruction can take place in manganese cluster (two-nucleus or four-nucleus) under the action of radiation [8, 9] from univalent state (4.9369 eV – this is similar to initial values of Mg РE-parameter) to bivalent (9.9414 eV) and further – to quadrivalent state (17.518 eV). All this provides enzymatic action of Mn upon the bond Н-О-Н, both upon oxygen and hydrogen atoms, and hydroxyl group in general. This is confirmed by the approximate equality of РE-parameters of bi- and quadrivalent Mn with РE-parameters of 2Р1 and 2Р2orbitals of oxygen atom (table 3). Thus, all the above interactions and structural re-groupings inducted with light result in the formation of oxidized chlorophyll based on the following reaction [10]: Н2О+2hν→

1 О2+2е-+2Н+ 2

with the isolation of two electrons and two protons. These electrons, broken off from the water, through the chain of “dark” reactions go further to PS-1 that utilizes them in the next photosynthesis stages to reduce NADP+ to NADPN that is carried out also with the help of proton transfer system. For double bond of 2Р1-orbital the carbon atom has РE-parameter – (8.5043 eV) – similar to РE-parameter of hydrogen atom (table 1). Therefore one of the freed hydrogen atoms join the double bond С=С available in NADPN with the formation of single bond with carbon atom [9].

PHOSPHORYLATION It is considered [7,11] that directed transition of protons serves as energy source during phosphorylation. Between the numbers of transported protons and electrons certain stoichiometric relations are revealed. Thus, in the course of electron transfer (along the whole transport system) ATP molecules are formed. Apparently, ATP phosphorylation energy can also be estimated through the system of electron transfer. In particular, electron transfer results in that phosphoric acid molecules present in АТP, NADP and NADPN contain oxygen atoms in the form of О-. Spatial-energy interactions (including isomorphic) are objectively expressed both at similar and opposite electrostatic charge of atoms-components. Such interactions can also take place between two heterogeneous atoms, if only their РE-parameters are roughly equal, and geometric shapes of orbitals are similar or alike. The radiation energy hν in PS-1 promotes, apparently, the changes in dimensional characteristics of phosphorous and oxygen atoms from covalent to anion ones. Therefore, Р0parameters of free phosphorus and oxygen atoms are distributed at the distance of their anion radii 1.86 Å and 1.40 Å, respectively. This similarity of values of their РE-parameters: α=5.19 % for 2Р3-orbitals of phosphorous with 2Р2-orbitals of oxygen (table 3). Such approximate equality of РE-parameters and geometric similarity of shapes of orbitals of atoms-components shows that actual degree of their interaction ρ=100 %, thus

Energy Criterions of Photosynthesis

83

providing the energy of formation of macroenergy bond Р-О. Then bond energy of phosphorous and oxygen atoms from two different molecules of phosphoric acid necessary for structural formation during phosphorylation can be considered phosphorylation energy. To calculate bond energies or energies of molecule reduction during photosynthesis (Е) the technique previously tested [6] for 68 binary and more complicated compounds following the equation was applied:

1 1 = = Е Рс ⎛

1

+

1

N⎞ ⎛ N⎞ ⎜ РE ⎟ ⎜ РE ⎟ ⎝ K⎠ ⎝ K⎠ 1

(10)

2

where N – bond average repetition factor, К – hybridization coefficient that usually equals the number of atom valence electrons registered. The half of internuclear distance (for binary bond) of similar atoms or atomic, covalence or ionic radii (depending upon bond type) can be used as a dimensional characteristic of atoms. The calculations involving anionic distances of atomic orbitals for Р and О atoms were made: 3Р1 (phosphorous)-2Р1 (oxygen) and for 3Р3 (phosphorous)-2Р2 (oxygen). The values of Е obtained appeared to be slightly greater than experimental and reference data (table 4). But actual power physiological processes during photosynthesis have the efficiency below the theoretical, being in some cases about 83% [7]. It is probable that electrostatic component of resulting interactions on anion-anion distances is registered in such a way. In fact, the calculated value 0.83Е practically corresponds to the experimental bond energy values during phosphorylation (first line in table 4) and free energy for АТP in chloroplasts (second line in table 4). The calculations of bond energy based on the same technique but on covalence distances of atoms for free molecule Р…О (sesquialteral bond) and for molecule Р=О in Р4О10 (double bond) are given in table 4 for comparison. Sesquialteral bond was evaluated introducing the coefficient N=1.5 using the average value of oxygen РE-parameter for single and double bonds. It is interesting to point out that calculations of Е based on covalence distances correspond to experimental data without introducing the coefficient 0.83.

ASSIMILATION OF СО2 Binding of СО2 takes place in aqueous medium by the carboxylation reaction of ribulosediphosphate (RuDP) with the formation of 3-phospho-glycerine acid (PGA) – table 5. Water molecule and radical С=О at the distances of molecular interaction have quite similar values of РE-parameters for forming the general structural grouping of dimeric composite type. Total РE-parameter of water molecule and radical С=О nearly equals РE-parameter of СО2 and therefore the molecules of СО2 and Н2О join RuBP with the formation of two radicals СООН в PGA (table 5). In ferment RuDP- carboxylase, Mg atoms and О- ions (5.4867 eV and 4.755 eV) play an active role, their РE-parameters similar to РE-parameter of radical СООН.

Table 4. Bond and reduction energies of molecules during photosynthesis (eV) Atoms, structures, orbitals

1 component

2 component

РE (eV) 2 4.1862 4.1862 8.9215

N/K 3 1/5 1/5 1/5

РE (eV) 4 4.6188 4.755 8.470

N/K 5 1/6 1/6 1/6

Р---О 3S23P3-2S22P4

32.403

1.5/5

70.854 63.339

Р=О 3Р3-2P2 С-Н 2Р2-1S1 Н2О 1S1-2S2 -O-O2P1-2P1 O=O 2P2-2P2 CO2 2P2-2P2 =C=O 2S22P2-2P2 C-O 2P2-2P2 (C=O)-H (2S22P2-2P2)-1S1 -O-H 2P2-1S1 CO-OH (2S22P2-2P2)-(2P21S1) CH2O 2S22P2-1S1-2P2

15.085

2/3

13.066

1 Р-О 3Р1-2Р1 Р-О 3Р2-2Р2

3 component РE (eV) 6

N/K 7

Calculation Е 8 0.400 0.405 0.77

0.83Е 9 0.33 0.34 0.64

Е by [7.8.14]

Notes

-

10 0.340.35 0.670.59 6.14

Free PO molecule

-

6.504

In Р4О10 molecule

3.797

-

3.772

-

2.570

-

2.476

-

-

4.90

-

5.11

2/4

--

-

5.012

-

5.11

2•20.048

2/6

-

-

4.717

-

4.56

2/4

20.048

2/2

-

-

8.8874

-

13.066

1/2

17.967

1/2

-

-

3.782

-

3.688

31.929

2/4

20.048

2/2

9.0624

1/1

4.487

-

4.553

17.967 17.967 8.8874

1/2 1/2 1/1

17.137 9?0624 5.894

1/1 1/1 1/1

-

-

-

-.4.390

-

-

5.894 4.511 3.544

-

-

31.929

1.33/4

2.90624

1/1

20.048

2/2

5.025

-

4.965.07

_ _ -

-

1.5/6 1.5/6

-

-

20.042

2/2

-

-

6.277 6.024 < 6.15> 6.697

1/2

9.0624

1/1

-

-

2•9.0624

1/1

17.967

1/6

-

9.7979

1/1

9.7979

1/1

20.048

2/4

20.048

14.581

2/4

31.929

11 Phosphorylation ÄG of ATP

Decomposition of one molecule

Reduction

Free energy of the formation of one mole

Table 5. Spatial-energy characteristics of СО2 assimilation (eV)

Reaction blocks

PE

RuDF

Mg, RuDFcarboxylase

¾ C = O + H2O 8.4416

+ CO2

9.0226;

17.774;

NADPN, PGA ATP, O2COOH 2X5.1226 ;

PGA ATP Mg 2COH + O2 . . . 2x4.3705; 17.967x2 ;

EC

8.8874

2.570

EC1 =1.401

Calculation: EC2-EC1 =0.37; By [7]: 1 ATP molecule

4.717

3,544 3,544

4.487

5.012

EC3 =2.367

EC2 =1.770

9060

17.967x2

(7.333)

(8.741)

E

CH2O + O2 + . . .

5.025

5.012

EC4 =2.509

EC3-EC1 ~ 0.97 EC3-EC2 ~ 0.60 3 ATP molecule (1.06 eV) 2 ATP molecule

Notes: РE – initial values of РE-parameters, for Мg (5.4867), Mg2+ (8.6066), for О- (4.755; 4.6188) Е – bond or reduction energy ЕС – resulting bond or reduction energy for groups of radicals or fragments: 1/ЕС=1/Е1+1/Е2+…

86

G. А. Коrablev and G. Е. Zaikov

A great difference in the number of atoms of interacting structures proves that carboxylase can play only a fermentative role, “tuned” to obtain this final product (СООН). The further complicated way of СО2 assimilation to form СН2О flows through series of intermediate compounds and reactions (Calvin cycle). Let us show some results of calculations of total spatial-energy assimilation processes of СО2. When СО2 is reduced to the level of its structural formation in СН2О, the chemical bonds are reconstructed on all stages of the cycle. Therefore, the additional activation energy from ATP and NADPN is required. It is also obvious that power consumption should be rationally calculated taking into account the reconstruction processes of chemical bonds, i.e. via the values of bond energy – for binary structures, and reduction energy – for more complex molecules and radicals (Е). Thus we calculated the value E based on equation (10) for several compounds and radicals during photosynthesis – tables 4 and 5. For radical – С =О the calculations were made in two possible variants of activity of valence orbitals of carbon atoms. The compliance of calculated Е values with reference data [12,13] was in the range of 5% for all bonds of covalence type without introducing the coefficient 0.83. The main part of light energy is stored by a plant on the reduction stage to PGA. At the same time, 4.56 eV (per molecule) are spent – [12.13]. Our calculations give the reduction energy of radical СОН equal to 4.487 eV. Free energy for the formation of one mole of СН2О based on reference data [7,12, etc] is 4.96-5.07 eV. The calculations following the method of Р-parameter evaluate this energy as 5.025 eV. Н In molecule О=С–Н the average repetition factor for carbon atom bond was taken as equal to (2+1+1)/3=1.33. Applying the approved approach to calculate the resulting bond energy (or the reduction energy) of structural subsystems for each stage, the values of these energies were calculated (table 5) – ЕС. It is known [7] that the cycle moving energy to PGA can be 1.06 eV due to three ATP molecules (per one СО2 molecule), one ATP molecule is consumed in the cycle to PGA. Following our data, the cycle moving energy (ΔЕС) equals the difference of ЕС values for the corresponding stages: 1) stage СО2 – FGAК: ΔЕС=1.770-1.401=0.369 eV Phosphorylation energy of one ATP molecule = 0.34-0.35 eV 2) stage СО2 – FGA: ΔЕС=2.367-1.401=0.966 eV Phosphorylation energy of three ATP molecules: 0.34х3=1.02 eV Thus Р-parameter gives the satisfactory characteristics of energetics of the СО2 assimilation cycle main stages. Photorespiration reaction is as if “competitive” to the СО2 assimilation reaction. Also here it is possible to reveal similar values of РE-parameters of interacting radicals С=О and НСОН with РE-parameters of oxygen atoms. As in assimilation reaction the ferment RuDP- carboxylase “is tuned” for the formation of final product СООН. Other ferments can participate in photosynthesis and photorespiration, for example, the substitution of Mg atoms for Fe atoms results in the formation of cytochromes, in which РEparameter of two-valence iron (РE=10.093 eV) is an active spatial-energy component of photosynthesis structural interactions. Therefore, iron-sulfur proteins – ferrdoxins executing

Energy Criterions of Photosynthesis

87

various transport functions connected with ATP synthesis are initial and secondary acceptors of electrons in the system PSI.

CONCLUSION In this approach we give quantitative and semi-quantitative evaluation of spatial-energy interactions at main stages of complicated biophysical process of photosynthesis based on the utilization of initial atomic characteristics. The analysis of results after the application of Рparameter methodology shows that they correspond to reference data both in the direction and energetics of these processes.

REFERENCES [1] [2] [3] [4] [5] [6]

[7] [8] [9] [10] [11] [12] [13] [14]

Big medical encyclopedia. М.Т.26.1985.560 p. Korablev G.A. Spatial-Energy Principles of Complex Structures Formation. Netherlands. Brill Academic Publishers and VSP. 2005, 426p. (Monograph). Fischer C.F. Average-Energy of Configuration Hartree-Fock Results for the Atoms Helium to Radon.//Atomic Data.-1972. -№ 4. -p. 301-399. Waber J.T.. Cromer D.T. Orbital Radii of Atoms and Ions//J. Chem. Phys -1965. -V 42. -№12. -p. 4116-4123. Clementi E.. Raimondi D.L. Atomic Screening constants from S.C.F. Functions. 1.//J.Chem. Phys.-1963. -v.38. -№11. -p. 2686-2689. Korablev G.A.. Zaikov G.E. Energy of chemical bond and spatial-energy principles of hybridization of atom orbitalls.//J. of Applied Polymer Science. USA. 2006. V.101.n3.P.2101-2107. Photosynthesis/Edited by Govingi. М.:Mir, V.1-1987, 728p; V.2-1987, 460p. P. Clayton. Photosynthesis. Physical mechanisms and chemical models. М.:Mir-1984, 350p. S.A. Schukarev. Inorganic chemistry. V.2-1974, 382p. D. Hall, K. Rao. Photosynthesis. М.:Mir, 1983. J. Edwards, D. Walker. Photosynthesis of С3 and С4-plants: Mechanisms and regulation. М.: 1986. Encyclopedia in physics. М.: 1966, V.5, 576p. Kamen M.D. Primary processes in photosynthesis. L. 1963. Break-off energy of chemical bonds. Potentials of ionization and affinity to electron / Edited by V.I. Kondratjev. М.:Nauka, 1974, 351p.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 89-101 © 2007 Nova Science Publishers, Inc.

Chapter 8

SPATIAL-ENERGY INTERACTIONS OF FREE RADICALS G. А. Коrablev*1 and G. Е. Zaikov*2 1

Basic research-educational center of chemical physics and mesoscopy, Udmurt research center, Ural Division, RAS, Izhevsk 2 Institute of biochemical physics after N.M. Emanuel, RAS, 119991, 4 Kosygina St.; Russia, Moscow

ABSTRACT Spatial-energy characteristics of many molecules and free radicals are obtained. The possibilities of applying the P-parameter methodology to structural interactions with free radicals and photosynthesis energetics evaluation are discussed. The satisfactory compliance of calculations with experimental and reference data on main photosynthesis stages is shown.

Keywords: Spatial-energy parameter, free radicals, structural interactions, photosynthesis.

DESIGNATIONS m1 and m2 а Δх ΔU1 and ΔU2 ΔU Z* n* * *

masses of material points (kg); their acceleration (m/s2); coordinate (m); potential energies of material points (J); their resulting (mutual) potential energy of interaction (J); nucleus effective charge (Cl); effective main quantum number;

G.А. Коrablev: E-mail: [email protected] G.Е. Zaikov: E-mail: [email protected]

G. А. Коrablev and G. Е. Zaikov

90 Wi ri ni SEI Р0 РE R N1, N2, … РС Ψ α ρ

bond energy of electrons on i-orbital (eV); orbital radius of i-orbital (Å); number of electrons on this orbital; spatial-energy interactions; spatial-energy parameter (eVÅ); effective Р-parameter (eV); dimensional characteristic of atom or chemical bond (Å); number of homogeneous atoms; Р-parameter of complex structure (eV); Ψ-function; coefficient of structural interactions, isomorphism (%); degree of structural interaction (%).

INTRODUCTION Free radicals are the atom groups or molecule fragments having unpaired electrons. Most of them are unstable with high reactivity. Interacting between themselves and with other molecules they produce new compounds that continue chemical reactions based on chain principle – similar to neutrons in chain nuclear reactions. In many cases such processes are the main reason of pathologic condition of living systems [1]. Therefore the problem of searching “retardants” for these chain reactions of free radicals is critical. For instance, it is known that sulfur-containing amino acid (cysteine) “attracts” unpaired electrons of protein [2,3]. Similar properties are reported about selenium, the element of the same subgroup VI-а of the System as sulfur [4]. It is found out that the number of unpaired electrons in dry bio-objects (after their production) decreases when introducing nitric oxide or increasing the moisture content. On the contrary, the role of oxygen atoms (also the element of VI-а subgroup of the System) is often expressed as the role of an accelerator of irreversible reactions of free radicals. Free radicals (including oxygen) demonstrate specific influence in complicated biophysicochemical processes of photosynthesis. Fundamental regularities of reactions with free radicals were found by I.I. Semenov and his disciples. Important contribution to solving the problem of free radical participation in biological processes was made by N.M. Emmanuel, А.G. Gurvich, B.N. Tarusov, L.А. Bluemenfeld, G.М. Frank, W. Gordy, B. Commoner, M.J. Calvin and others. It seems interesting to find a functional dependence and directedness of free-radical processes with initial energy and dimensional characteristics of their atomscomponents. In this paper we are attempting to explain such processes applying the methodology of spatial-energy notions (P-parameter).

Spatial-Energy Interactions of Free Radicals

91

METHODOLOGY SUBSTANTIATION Comparing multiple regularities of physical and chemical processes we can assume that in many cases the principle of adding reciprocals of volume energies or kinetic parameters of interacting structures is implemented. Some examples: ambipolar diffusion, total rate of topochemical reaction, change in the light velocity when transiting from vacuum into the given medium, resulting constant of chemical reaction rate (initial product – intermediary activated complex – final product). Lagrange equation for relative movement of isolated system of two interacting material points with masses m1 and m2 in coordinate х with acceleration α can be presented as follows:

1 ≈ − ΔU 1 /( m 1 aΔx) + 1 /( m 2 aΔx)

1 or:

ΔU

≈

1

ΔU 1

+

1

ΔU 2

(1)

where ∆U1 and ∆U2 – potential energies of material points in elementary section of interactions, ΔU - resulting (mutual) potential energy of these interactions. The atom system is formed from oppositely charged masses of nucleus and electrons. In this system energy characteristics of subsystems are the orbital energy of electrons (Wi) and effective energy of nucleus that takes into consideration the screening effects (by Clementi). Therefore, assuming that the resultant interaction energy of the system orbital-nucleus (responsible for interatomic interactions) can be calculated based on the principle of adding reciprocals of some initial energy components, we substantiate the introduction of Pparameter [5] as an averaged energy characteristic of valence orbitals in accordance with the following equations:

1

1

+

=

1

q r Wn Р 2

i

i

Р

E

Р r

=

i

0

(2) E

(3)

i

1

=

1 2

P0

q

q=

Z* n*

+

1 (Wrn) i

(4)

(5)

G. А. Коrablev and G. Е. Zaikov

92

Here: Wi – bond energy of electrons [6]; ri – orbital radius of i–orbital [7]; ni – number of electrons of the given orbital, Z* and n* – effective charge of nucleus and effective main quantum number [8]. The Р0 value will be called a spatial-energy parameter, and the РE value – effective Р– parameter. Effective РE–parameter has a physical sense of some averaged energy of valence electrons in atom and is measured in energy units, e.g. in electron-volts (eV). Based on the results [5] the values of РE-parameters numerically equal (within 2%) total energy of valence electrons (U) by the atom statistic model. Using the well-known ratio between electron density (β) and inneratomic potential by the atom statistic model, we can obtain the direct dependence of РE-parameter upon the electron density at the distance ri from the nucleus:

β

2 i

3

= A P0 =

r

AP

E

where А – constant

i

Validity of this equation was confirmed when calculating the electron density using Clementi’s wave functions and comparing it with electron density value calculated via РEparameter value. Besides the modules of maximum values of ψ-function radial part were compared with Р0-parameter values, and the line dependence between these values was found. Using some properties of wave function for P-parameter, the wave equation of P-parameter was obtained. Based on calculations and comparisons two principles of adding spatial-energy criterions depending upon wave properties of P-parameter and systemic character of interactions and charges of particles were substantiated: 1. Interaction of oppositely-charged (heterogeneous) systems consisting of I, II, III, ... atom sorts is satisfactorily described by the principle of adding corresponding energy reciprocals by equations (2-5) (this corresponds to the minimum of weakening oscillations taking place in antiphase); 2. During the interaction of similarly-charged (homogeneous) subsystems the principle of algebraic adding of their P-parameters is realized based on the following equations:

m Σ Р0= P'0+ P'0' +...+ P0m i =1

(6)

∑ РE =

∑ Р0 R

(7)

where R –dimensional characteristic of atom (or chemical bond). This principle corresponds to the maximum of oscillation intensification taking place in the phase. Modifying the rule of adding energy reciprocals of subsystems as applied to complex structures we can obtain the equation for calculating РС-parameter of complex structure:

Spatial-Energy Interactions of Free Radicals

1 ⎛ 1 ⎞ ⎛ 1 ⎞ ⎟ +⎜ ⎟ + ... =⎜ Pc ⎜⎝ NPE ⎟⎠1 ⎜⎝ NPE ⎟⎠ 2

93

(8)

where N1 and N2 – number of homogeneous atoms in subsystems. During the formation of solution and other structural interactions the same electron density must be formed in the areas of contact of atoms-components. This process is accompanied by the redistribution of electron density between valence zones of both particles and transition of a part of electrons from some outer spheres into neighboring ones. Apparently, spanning electrons of atoms do not participate in such an exchange. Apparently, with the closeness of electron densities in free atoms-components, the transition processes between boundary atoms of particles will be minimum, thus favoring the formation of new structure. So, the evaluation of the degree of structural interactions in many cases comes to the comparative evaluation of electron density of valence electrons in free atoms (on averaged orbitals) participating in the process. The less is the difference (Р'0/r'i – P"0/r"i), the more favorable is the formation of a new structure or solid solution from energy point. In this connection the maximum total solubility evaluated through the coefficient of structural interaction α is defined by the condition of minimum value of α that represents a relative value of effective energies of outer orbitals of interacting subsystems:

P 'o / ri '− P ''o / ri '' α= 100% ( P 'o / ri '+ P ''o / ri '') / 2

' − Р" РС С 200% (9a) α = ' + Р" РС С

(9)

The nomogram of dependence of structural interaction degree (ρ) upon the coefficient α, unified for a broad range of structures was designed based on all the data obtained. Figure 1 shows the nomogram obtained using РE-parameters calculated via the bond energy of electrons (wi) for structural interactions of isomorphic type. Following this methodology the mutual solubility of atoms-components was evaluated in many (over a thousand) simple and complex systems. The calculation results agree with reference and experimental data. Isomorphism as a phenomenon is used to be applied to crystalline structures. Apparently, analogous processes can also take place between molecular compounds where their role and significance are no less than of purely coulomb interactions. In complex organic structures the main role can be performed by separate “blocks” or fragments. Therefore the task is to identify these fragments and evaluate their spatial-energy parameters. According to wave properties of Р-parameter, total Р-parameter of each fragment has to found based on the principle of adding reciprocals of initial P-parameters of all the atoms. The resultant Р-parameter of fragment block or all the structure is calculated following the rule of algebraic adding of P-parameters of fragments constituting them. The role of fragments can be performed by valence-active radicals, e.g. СН, СН2, (ОН)-, NO, NO2, (SO4)2-, etc. In complex structures this carbon atom usually has not one, but two or three side bonds. The priority significance when calculating based on the principle of adding

G. А. Коrablev and G. Е. Zaikov

94

reciprocals of P-parameters have those bonds, for which the condition of interference minimum is better executed. Therefore first the fragments of bond С-Н (for СН, СН2, СН3 …) are calculated, and then separately the fragments N-R, where R-binding radicals (e.g. – for the bond C-N).

Figure 1. Nomogram.

Apparently, spatial-energy interactions (SEI) based on equalization of electron densities of valence orbitals of atoms-components have in nature the same universal significance as purely electrostatic coulomb interactions, but they supplement each other. Isomorphism known from the time of E. Micherlikh (1820) and D.I. Mendeleev (1856) is only a particular manifestation of this overall natural phenomenon. The quantitative side of evaluating isomorphic replacements of components, both in complex and simple systems, can be rationally placed in the frameworks of P-parameter methodology. The problem of evaluating the degree of structural SEI for molecular and organic structures is more complicated. The methodology for calculating P-parameters of molecules, structures and their fragments are successfully implemented [5]. But such structures and their fragments are not often completely isomorphous to each other. Nevertheless SEI proceeds between them, its degree can be evaluated only semi-quantitatively or qualitatively. All systems can be split into three types based on their isomorphous similarity: I Systems mainly isomorphous to each other – the systems with almost the same number of heterogeneous atoms and summarily similar geometric shapes of interacting orbitals. II Systems with limited isomorphous similarity – the systems that: 1. either differ in the number of heterogeneous atoms but have summarily similar geometric shapes of interacting orbitals;

Spatial-Energy Interactions of Free Radicals

95

2. or definitely differ by geometric shape of orbitals but have the same number of interacting dissimilar atoms. III Systems without isomorphous similarity – the systems that considerably differ both in number of dissimilar atoms and geometric shape of their orbitals. Then, taking into account some experimental data, all types of SEI can be approximately classified as follows: Systems I 1. α < (0-6)%; ρ = 100 %. Complete 100% isomorphism, complete isomorphous replacement of atoms-components; 2. 6 % < α < (25-30)%; ρ = 98 – (0-3) %. Either broad or limited isomorphism as shown in nomogram 1; 3. α > (25-30) %; no SEI Systems II 1. α < (0-6)%; a. а) Reconstruction of chemical bonds, can be accompanied with the formation of a new compound; b. b) Breaking of chemical bonds can be accompanied with the separation of a fragment from the initial structure, but without joining or replacing. 2. 6 % < α < (25-30)%; A limited internal reconstruction of chemical bonds without the formation of a new compound and replacements is possible. 3. α > (20-30) %; no SEI Systems III 1. α < (0-6)%; a. а) Limited change in the type of chemical bonds of the given fragment, internal regrouping, without breaking from the main part of the molecule and replacements is possible; b. b) Some dimensional characteristics of the bond can change; 2. 6 % < α < (25-30)%; A very limited internal regrouping of atoms; 3. α > (25-30) %; no SEI. Nomogram № 1 is made for isomorphous interactions, i.e. for such structures or subsystems with the same number of dissimilar atoms and approximate geometric resemblance of interacting atomic orbitals.

G. А. Коrablev and G. Е. Zaikov

96

In all other cases the calculated values of α and ρ refer only to the given type of interactions, nomogram of which is not yet existing, and all the comparisons are merely assumptions of qualitative or semi-quantitative character. But if taking into account the universality of spatial-energy interactions in nature, this evaluation can be significant for analyzing structural rearrangements in complex biophysicochemical processes (this will be further shown on the example of photosynthesis). Enzymatic systems can greatly contribute to the correlation of the degree of structural correlations. In this model the enzyme role is as follows: active parts of its structure (fragments, atoms, ions) the РE-parameter value equal to the РE-parameter of the reaction final product. I.e. the enzyme is structurally “tuned” via ПЭВ to obtaining the reaction final product, but will not join it due to imperfect isomorphism of its structure (in accordance with III).

CALCULATIONS AND COMPARISONS Based on equations (2-5) with initial data calculated with quantum-mechanical techniques [6-8], the values of Р0-parameters of the majority of elements being tabulated constant values for each valence atom orbital were calculated. Mainly covalent radii were applied as a dimensional characteristic for calculating РE-parameter – by main type of chemical bond of interactions considered (table 1). For hydrogen atom also the value of Bohr radius and value of atomic (“metal”) radius were applied. In some cases the calculations of P-parameters are given considering the possibility of hybridization of atom orbitals (marked with “Г”) – following the methodology discussed before [9]. Besides we took into account the bond repetition factor for carbon and oxygen atoms. In the course of calculations for potassium atom – element of group IV of large period in the System the possibility of the influence of internal d-orbitals was considered. For several elements the values of РE-parameters were calculated using ionic radii whose values are given in column 7. All the values of atomic, covalent and ionic radii are basically taken by BelovBokiy, but crystalline ionic radii – by Batsanov [10]. Table 1. Р-parameters of atoms calculated via bond energy of electrons Atom 1 Н

Valence electrons 2

1S

1

W (eV) 3

13.595

ri (Å) 4

0.5295

q2 0 (eVÅ) 5

14.394

Р0 (eVÅ) 6

4.7985

R (Å) 7 0.5295 0.46 0.28 R-I=1.36

Р0/R (eV) 8 9.0624 10.432 17.137 3.525

Spatial-Energy Interactions of Free Radicals

97

Table 1. (Continued) Atom

С

N

1

Valence electrons

W (eV)

ri (Å)

q2 0 (eVÅ)

Р0 (eVÅ)

R (Å)

Р0/R (eV)

2P1

11.792

0.596

35.395

5.8680

2P2

11.792

0.596

35.395

10.061

0.77 0.69 0.77 0.69

7.6208 8.5043 13.066 14.581

0.77 0.77 0.77 0.77 0.77 0.70 0.70 0.70 0.55 0.55 0.70 0.70 0.70 7 0.66 RI=1.36 RI=1.40 0.66 0.59 RI=1.36 RI=1.40 0.66 0.59 0.66 0.66 0.66 0.59 1.97 1.97 R2+=1.00 R2+=1.26 1.04 1.04 1.04 1.04

11.715 18.862 28.875 17.435 31.929 9.4166 16.747 22.614 34.896 39.938 15.299 25.476 48.09 8 9.7979 4.755 4.6188 17.967 20.048 8.7191 8.470 30.815 34.471 19.082 32.524 63.339 70.854 3.0096 4.4902 8.8456 7.0203 7.7061 13.215 20.553 13.134

1.04 1.17 1.17 1.6 1.14 1.17 1.6 1.17 1.17 1.17 1.6

42.250 7.3343 12.880 9.4188 13.219 20.710 15.133 12.515 21.376 42.066 30.759

2Р1г 2P3г 2S1 2S2 2S1+2P3г 2S1+2P1г 2S2+2P2 2P1 2P2 2P3 2P4г 2P5г 2S1 2S2 2S2+2P3 2 2P1 2P1 2P1 2P2

19.201

0.620

37.240

15.445

0.4875

52.912

25.724 25.724

0.521 0.521

53.283 53.283

3 17.195

4 0.4135

5 71.383

4.4044 13.213 9.0209 14.524 22.234 13.425 24.585 6.5916 11.723 15.830 19.193 21.966 10.709 17.833 33.663 6 4.663

17.195

0.4135

71.383

11.858

2P4

17.195

0.4135

71.383

20.338

2S1 2S2 2S2+2P4

33.859 33.859

0.450 0.450

72.620 72.620

12.594 21.466 41.804

5.3212

1.690

17.406

5.929 8.8456

O

Ca

S

Se

4S1 4S2 4S2 4S2 3P1 3P2 3P4 3S1 3S2 3S2+3P4 4P1 4P2 4P2 4P2 4P4 4P4 4S1 4S2 4S2+4P4 4S2+4P4

11.901 11.901 11.904 23.933 23.933

0.808 0.808 0.808 0.723 0.723

48.108 48.108 48.108 64.852 64.852

10.963

0.909

61.803

22.787

0.775

85.678

6.0143 13.740 21.375 13.659 22.565 43.940 8.5811 15.070 15.070 15.070 24.213 14.642 25.010 49.214 49.214

G. А. Коrablev and G. Е. Zaikov

98

Table 1. (Continued)

Atom

Р

Mg

Mn

Valence electrons

W (eV)

ri (Å)

q2 0 (eVÅ)

Р0 (eVÅ)

R (Å)

Р0/R (eV)

3P1 3P1 3P3 3P3 3S2 3S2+3P3 3S1 3S2

10.659

0.9175

38.199

7.7864

10.659

0.9175

38.199

16.594

18.951

0.803

50.922

6.8859

1.279

17.501

19.050 35.644 5.8568 8.7787

4S1 4S2 3d1 4S1+3d1 4S2+3d2 4S2+3d5 3S1

6.7451

1.278

25.118

17.384

0.3885

177.33

4.9552

1.713

10.058

4.6034

3P1

13.780

0.7235

59.849

8.5461

2 4S1 3d1 4S1+3d1 4S2+3d1 4S1

3 7.0256 17.603

4 1.227 0.364

5 26.572 199.95

6 6.5089 6.2084 12.717 16.664 4.8490

1.10 R3-=1.86 1.10 R3-=1.86 1.10 1.10 1.60 1.60 R2+=1.02 1.30 1.30 1.30 1.30 1.30 1.30 1.89 R+I=1.18 R+I=0.98 1.00 R-I=1.81 7 1.26

7.0785 РE=4.1862 15.085 8.9215 17.318 32.403 3.6618 5.4867 8.6066 4.9369 7.8638 5.0043 9.9414 17.518 29.684 2.4357 3.901 4.6973 8.5461 4.7216 8 4.8325

1.26 1.26 2.36 R+I=1.45 2.36 R+I=1.45

10.093 13.226 2.0547 3.344 3.0557 4.9734

6.4180 10.223 6.5058 12.924 22.774 38.590

Na Cl 1 Fe

К

4S2(*)

4.0130

2.612

10.993

7.2115

Table 2 contains the computational results of structural РС-parameters of free radicals by the equation (8). The calculations are made for those radicals forming protein and aminoacid molecules (СН, СН2, СН3, NH2, etc), as well as for free radicals being formed during radiolysis and dissociation of water molecules (Н, ОН, Н3О, НО2). The comparison of РС-parameter values of free radicals obtained with carbon, sulfur, selenium and oxygen atoms was carried out in supposition of paired interactions by all possible variants – based on the equation (9). It should be specifically stressed that here we have the calculations of РE-parameters and structural interactions of practically all possible values of initial dimensional characteristics of atoms. In the norm of stable bonds without external interactions covalent bonds are the most probable in organic molecular structures. The other options of SEI given in tables 1-3 correspond to such possible structural regrouping when due to some reasons their dimensional characteristics vary from covalent to atomic or even ionic. The results of such calculations of coefficient α and degree of structural interactions (ρ) are given in table 3, when analyzing it the following conclusions and comparisons can be made: 1. Valence orbitals of sulfur and selenium atoms have quite similar values of Pparameters as well as the degrees of structural interactions (ρ). On the contrary, РE-parameters

Spatial-Energy Interactions of Free Radicals

99

of oxygen atoms sufficiently differ from such values thus resulting, in many cases, in the opposite results in chemical activity of its atoms. 2. Degree of structural interactions of sulfur and selenium atoms with radicals СН3, NH2,H3O equals 100%. But with radicals СН and СН2 it equals zero or is insignificant – in the range of 0 – 47%. It should be mentioned that structural interactions of the same elements with basic carbon chain of polymeric biomolecules cannot result in their breaking-in since the corresponding values of α for the interactions of Se-C and S-C exceeds 30%, thus ρ=0 in these cases. Atoms of S and Se can sufficiently structurally influence fragments of СН3 that are frequently located on the ends of hydrocarbon chains or in the form of free radicals. The data given confirm high reactivity of sulfur and selenium atoms as retardants of chain reactions of free radicals as elements “drawing back” unpaired valence electrons of free radicals, but at the same time preserving the basic structure of hydrocarbon chain. 3. Interactions of oxygen atoms result in α > 30% and ρ=0 with structures NH2, H3O and – with radicals СН and СН3 based on С atom (2S22P2). But for radical СН2 on the same base of carbon ρ=75-80 %, and for radical СН3 based on С atom (2S12P3г) – α=2,87 % and ρ=100 %. It is also important to add that in contrast to S and Se, atomic structures of oxygen and carbon have great values of РE-parameters and produce SEI at ρ=100 %. All this means that 1) degree and character of structural SEI of oxygen are ambiguous and considerably differ from the elements of selenium and sulfur; 2) oxygen atoms have potential possibilities for decomposing some molecular structures of bio-objects initiating the further free-radical process. 4. Water molecules (Н2О) produce ρ=100% with free radicals СН2, Н and ОН, this proves the possibility of decreasing the number unpaired electrons in dry bio-objects with their humidity decrease. In this approach the mechanism of radical Н3О formation during water dissociation can be apparently explained according to SEI (table 3). Hydrogen being released during dissociation by equation Н2О Н+ + ОН¯ further completely interacts with water molecules (as they have ρ=100%): Н+ + Н2О Н3О+. Table 2. Structural РС-parameters calculated via bond energy of electrons Radicals, fragments of molecules ОН

Н2О

СН2 СН3

Pi'

(eV)

17.967 9.7979 9.7979 17.967 2·9.0624 2·10.432 2·17.138 28.875 31.929 28.875 31.929 28.875

P "i (eV)

PC

10.432 9.0624 10.432 17.138 17.967 17.967 17.967 2·17.138 2·17.138 2·9.0624 3·17.138 3·9.0624

6.5999 4.7080 5.0525 8.7712 9.0226 9.6537 11.788 15.674 16.531 11.125 19.696 14.003

(eV)

Orbitals O (2P2) O (2P1) O (2P1) O (2P2) O (2P2) O (2P2) O (2P2) С (2S12P3г) С (2S22P2) С (2S12P3г) С (2S22P2) С (2S12P3г)

G. А. Коrablev and G. Е. Zaikov

100

Table 2. (Continued) Radicals, fragments of molecules СН NH NH2 Н3О Н2О–Н НО2 С2Н5 NO СН2 СН3 СН3 СН СН СО С=О С=О СО-Н2 С-О2 С-О2 СО-ОН NO CH-OH CO-H Se-H S-H Se-H S-H СО-СН3 SO2 SeO2

Pi'

(eV)

28.875 31.929 31.929 22.296 22.296 22.296 22.296 3·17.138 9.0226 17.138 2·31.929 22.296 31.929 28.875 31.929 28.875 31.929 31.929 14.581 17.435 12.315 28.875 31.929 12.315 22.614 11.152 8.4416 12.880 13.215 12.880 13.215 12.315 20.533 20.710

P "i (eV)

PC

17.138 9.0624 17.138 9.064 17.138 2·9.0624 2·17.138 17.967 9.0624 2·17.967 5·17.138 17.967 2·9.0624 3·17.138 3·9.0624 10.432 10.432 20.048 20.048 20.048 2·9.0624 2·20.048 2·20.048 8.7712 17.967 8.7712 9.0624 9.0624 9.0624 17.137 17.137 8.7712 2·20.048 2·20.048

10.755 7.059 11.152 6.4370 12.019 9.9980 13.509 13.314 4.5212 11.604 36.590 9.9495 11.562 18.491 14.684 7.6634 7.8630 12.315 8.4416 9.3252 7.3330 16.786 17.774 5.1226 10.012 4.9159 4.3705 5.3194 5.3758 7.3533 7.4615 5.1226 13.579 13.656

(eV)

Orbitals С (2S12P3г) С (2S22P2) С (2S22P2) N(2P3) N(2P3) N(2P3) N(2P3) O (2P2) O (2P2) O (2P2) С (2S22P2) N(2P3) С (2S22P2) С (2S22P3г) С (2S22P2) С (2S22P3г) С (2S22P2) С (2S22P2) С (2P2) С (2S12P1г) С (2S22P2) С (2S12P3г) С (2S22P2) С (2S22P2) N(2P3) С (2S22P2) С (2P2) Se (4P2) S (3P2) Se (4P2) S (3P2) С (2S22P2) S (3P2) Se (4P4)

GENERAL CONCLUSIONS 1. Oxygen and its systemic fragments initiate free-radical processes normally producing the rational balance with all forms of active protection of macromolecules from them; in particular, atoms of sulfur and selenium can be applied for that. 2. Spatial-energy characteristics of different valency for sulfur and selenium define the possibility of formation of such structures with these elements that possess multipronged physical and chemical properties from poisons to oxidants. 3. Methodology of spatial-energy parameter helps not only to explain experimentally determined dependencies of interactions of these elements with free radicals, but also provides practical solution for searching new reagents with given properties.

Spatial-Energy Interactions of Free Radicals

101

Table 3. Evaluation of the degree of structural interactions (ρ) Atoms, molecules, radicals 1 Se–CH3 S–CH3 О–CH3 Se–C О-С О-С S–C O-H O-H2 O-H H2O-H H2O-OH OH-H Se-CH3 Se–H3O S–H3O O–H3O O-CH2 O-CH Se-NH2 S-NH2 O-NH2 O-CH3 S-CH3 O-S О–CH2 Se–CН S–CН Se–CН2 S–CН2 Se–CН2 S–CН2 Se–CН S–CН

1 component Orbitals РE , РС (eV) 2 3 4Р4 20.710 3Р4 20.553 2Р4 30.815 4Р4 20.710 2Р4 30.815 2Р2 17.967 3Р4 20.533 2Р2 17.967 2Р2 17.967 2Р1 9.7979 1S1-2Р2 9.0226 2Р2-1S1 8.7712 4Р2 13.219 4Р2 12.880 4Р2 12.880 3Р2 13.215 2Р2 17.967 2Р2 17.967 2Р1 9.7979 4Р2 12.880 3Р2 13.215 2Р2 17.967 2Р2 17.967 3Р2 13.215 2Р2 20.048 2Р2 17.967 4Р4 20.710 3Р4 20.553 4Р4 20.710 3Р4 20.553 4Р2 12.880 3Р2 13.215 4Р2 12.880 3Р2 13.115

2 component Orbitals РE , Р С (eV) 4 5 2S22P2-1S1 19.696 2S22P2 19.696 2S22P2 19.696 2S22P2 31.929 2S22P2 31.929 2S12P1 г 17.435 2S22P2 31.929 1S1 17.138 1S1 9.0624 1S1 9.0624 1S1 9.0624 1S1 9.0624 2S12P3 г-1S1 14.003 1S1-2P2 13.314 1S1-2P2 13.314 1S1-2P2 13.314 1S1-2P2 13.314 2S22P2-1S1 16.531 2S22P2-1S1 7.059 2P3-1S1 13.625 2P3 13.625 2P3 13.625 2S12P3 18.491 2S1P3 г-1S1 14.003 3Р4 20.533 2S12P3г-1S1 11.125 2S22P2-1S1 11.152 2S22P2 11.152 2S22P2 16.531 2S22P2 16.531 2S22P2 11.562 2S22P2 11.562 2S22P2 11.152 2S22P2 11.152

α (%)

6 5.02 4.16 44 42.6 3.55 3.01 43.4 4.72 0.88 7.80 0.40 2.83 3.27 5.76 2.56 0.75 29.7 8.33 32.15 5.62 3.06 27.5 2.87 5.76 2.39 34 60 59.3 22.4 21.7 10.8 13.3 14.4 16.9

ρ (mol%) 7 100 100 0 0 100 100 0 100 100 84-88 100 100 100 100 100 100 0 75-80 0 100 100 0 100 100 100 0 0 0 2-5 2.5-5.5 7 47-52 30-35 23-28

Assumed SEI type 8 III, 1 III, 1 III, 3 I, 3 I, 1 I, 1 I, 1 II, 1 II, 1 II, 1 II, 1 II, 1 II, 1 III, 1 III, 1 III, 1 III, 3 III, 2 III, 3, II, 3 III, 1 III, 1 III, 3 III, 1 III, 1 I, 1 II, 3, III, 3 III, 3 III, 3 III, 3 III, 3 III, 2 III, 2 III, 2 III, 2

REFERENCES [1] [2] [3]

[4]

А.G. Golubev. Biochemistry of life extending // Success in gerontology-2003Iss.12,p.57-76. P.A. Alexander. Nuclear radiation and life. Translated from English. М.: 1959. Brack C.,Bechter-Thuring E and Labuhn M. N-acetylrysteine clows down ageing and increases the life span of Drosophila melanogaster//Cell Mol. Life Sci.-1977 vol 53/P960-966. Beziepkin V.G., Sirota N.P. and Gaziev A.L. The prolongation of survival in mice by dictary antioxidants depends on their age by the start of feeding this diet//Mech. Ageing Dev.-1996.-vol 92.-P.227-234.

102 [5]

G. А. Коrablev and G. Е. Zaikov

Korablev G.A. Spatial-Energy Principles of Complex Structures Formation, Netherlands, Brill Academic Publishers and VSP, 2005,426p. (Monograph). [6] Fischer C.F. Average-Energy of Configuration Hartree-Fock Results for the Atoms Helium to Radon.//Atomic Data,-1972, -№ 4, -p. 301-399. [7] Waber J.T., Cromer D.T. Orbital Radii of Atoms and Ions//J. Chem. Phys -1965, -V 42, -№12, -p. 4116-4123. [8] Clementi E., Raimondi D.L. Atomic Screening constants from S.C.F. Functions, 1.//J.Chem. Phys.-1963, -v.38, -№11, -p. 2686-2689. [9] Korablev G.A., Zaikov G.E. Energy of chemical bond and spatial-energy principles of hybridization of atom orbitalls.//J. of Applied Polymer Science. V.101,n.3,Aug.5,2006,p.2101-2107. [10] S.S. Batsanov. Structural chemistry. Facts and dependencies. М.:MSU-2000,292p.

In: Organic and Physical Chemistry Using Chemical Kinetics … ISBN: 978-1-60021-763-0 Editors: Y.G. Medvedevskikh, et al. pp. 103-166 © 2007 Nova Science Publishers, Inc.

Chapter 9

POLY (VINYL ALCOHOL)[PVA]-BASED POLYMER MEMBRANES: SYNTHESIS AND APPLICATIONS Silvia Patachia,a Artur J. M. Valente,b Adina Papanceaa and Victor M. M. Lobob a

Department of Chemistry, “Transilvania” University of Brasov, 29 Eroilor Street, 500036 Brasov, Romania. b Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal

1. INTRODUCTION Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various pharmaceutical, biomedical, and separation applications. PVA has a relatively simple chemical structure with a pendant hydroxyl group (figure 1a). The monomer, vinyl alcohol, does not exist in a stable form, rearranging to its tautomer, acetaldehyde. Therefore, PVA is produced by the polymerization of vinyl acetate to poly(vinyl acetate) (PVAc) followed by the hydrolysis to PVA (figure 2). Once the hydrolysis reaction is not complete, there are PVA with different degrees of hydrolysis (figure 1b). For practical purposes, PVA is always a co-polymer of vinyl alcohol and vinyl acetate [1].

H2C

CH OH a.

Figure 1. Continued.

n+m

104

Silvia Patachia, Artur J. M. Valente, Adina Papancea et al.

H2C

CH OH

CH2

CH O

n

C

O

CH3

m

b. Figure 1. Molecular strucuture of PVA fully hydrolyzed (a) and partially hydrolyzed (b).

n H2C

initiator

CH

*

CH2

CH

*

O

OCOCH3

Vinyl acetate

COCH3

n

Poly(vinyl acetate) a.

*

CH2

CH

*

+ n CH3OH

O COCH3

n

NaOH

*

CH2

CH

*

OH

n

Poly(vinyl alcohol)

Methanol

+

Poly(vinyl acetate)

n CH3OCOCH3 Methyl acetate b. Figure 2. Polymerization of vinyl acetate (a) and hydrolysis of PVAc to PVA (b).

PVA must be cross-linked in order to be useful for a wide variety of applications. A hydrogel can be described as a hydrophilic, cross-linked polymer, which can sorbe a great amount of water by swelling, without being soluble in water. Other specific features of hydrogels are their soft elastic properties, and their good mechanical stability, independent of the shape (rods, membranes, microspheres, etc.). PVA can be prepared by chemical or physical cross-linking; general methods for chemical cross-linking are the use of chemical cross-linkers or the use of electron beams or γ-

Poly(Vinyl Alcohol)[PVA]-Based Polymer Membranes…

105

radiation, whilst the most common method to produce physical cross-linking PVA is the socalled “freezing-thawing” process. PVA can be cross-linked [2] using cross-linking agents such as glutaraldehyde, acetaldehyde, etc. When these cross-linking processes are used in the presence of sulfuric acid, acetic acid, or methanol, acetal bridges form between the pendant hydroxyl groups of the PVA chains. As with any cross-linking compound, however, residual amounts are present in the PVA gel matrix; furthermore, other compounds such as initiators and stabilisers will reamin after synthesis. To use these gels for pharmaceutical or biomedical applications, we will have to extract all residues from the gel matrix. This is an extremely undesirable timeconsuming extraction process; also, if the process is not 100 % efficient and the residue is not completely removed, the gel will not be acceptable for biomedical or pharmaceutical applications. Other methods of chemical cross-linking include the use of electron beam or γirradiation. These methods have advantages over the use of chemical cross-linking agents as they do not leave behind toxic, elutable compounds. The minimum gelation dose of γ-rays (from 60Co sources) depends on the degree of polymerisation and the concentration of polymer in solution [3]. The effect of irradiation dose on the physical properties of PVA fibers, hydrogels and films irradiated in water is reported in [4-6]. The third mechanism of hydrogel preparation involves “physical” crosslinking due to crystallite formation [7]. This method addresses toxicity issues because it does not require the presence of a cross-linking agent (figure 3). Such physically cross-linked gels also exhibit higher mechanical strength than PVA gels crosslinked by chemical or irradiative techniques because the mechanical load can be distributed along the crystallites of the three-dimensional structure [1]. Some characteristics of these “physically” crosslinked PVA gels include a high degree of swelling in water, a rubbery and elastic nature, and high mechanical strength. In addition, the properties of the gel may depend on the molecular weight of the polymer, the concentration of the aqueous PVA solution, the temperature and time of freezing and thawing, and the number of freezing/thawing cycles [8-10].

Figure 3. Schematic representation of PVA gels formed by freezing/thawing process.

106

Silvia Patachia, Artur J. M. Valente, Adina Papancea et al.

PVA hydrogels have been used for numerous biomedical and pharmaceutical applications. PVA hydrogels are non-toxic, non-carcinogenic, show bioadhesive characteristics, and they are easily processed. The safety of PVA is based on the fact that the acute oral toxicity of PVA is very low, with LD50s (the amount of a material, given all at once, which causes the death – lethal dose - of 50 % of a group of test animals) in the range of 15-20 g/kg; when orally administered PVA is very poorly absorbed from the gastrointestinal tract; PVA does not accumulate in the body when administered orally; PVA is not mutagenic or clastogenic; and the no-observed adverse-effect level (NOAEL) of orally administered PVA in male and female rats were 5000 mg/kg body weight/day in the 90-day dietary study and 5000 mg/kg body weight/day in the two-generation reproduction study, which was the highest dose tested [11]. Furthermore, PVA gels exhibit a high degree of swelling in water and a rubbery and elastic nature. For all these features PVA is an excellent biomaterial. In fact, PVA is capable of simulating natural tissue and can be readily accepted into the body. PVA gels have been used for contact lenses, the lining for artificial organs, and drug-delivery applications. Recently, intelligent hydrogels have been used to produce micro- and nano-fabricated devices that seek to develop a platform of well controlled functions in the micro- and nano-level. For example, polymer surfaces in contact with biological fluids, cells, or cellular components can be tailored to provide specific recognition properties or to resist binding depending on the intended applications. Another recent application of PVA is related with the development of biomimetic methods to build biohybrid systems or even biomimetic materials for drug delivery, drug targeting, and tissue engineering devices. Besides all these applications, PVA is an important gel in different enginnering and industrial fields. For example, in the U.S.A., the majority of PVA is used in the textile industry as a sizing and finishing agent. PVA can also be incorporated into a water-soluble fabric in the manufacture of degradable protective apparel, laundry bags for hospitals rags, sponges, sheets, covers, as well as physiological hygiene products. PVA is also widely used in the manufacture of paper products. As with textiles, PVA is applied as a sizing and coating agent. It provides stiffness to these products making it useful in tube winding, carton sealing and board lamination. PVA is used as a thickening agent for latex paint and common house hold white glue or in other adhesive mixtures such as remoistenable labels and seals, as well as gypsum-based cements such that used for ceramic tiles. PVA is relatively insoluble in organic solvents and its solubility in aqueous solutions is adaptable to its necessary application [11]. The US Food and Drug Administration (FDA) allows PVA for use as an indirect food additive in products which are in contact with food [11]. For example, under 21 CFR 73.1, PVA is approved as a diluent in color additive mixtures for coloring shell eggs and under 21 CFR 349.12, PVA is approved as an ophthalmic demulcent at 0.1–4.0 %. Other applications of PVA are in areas of water and wastewater treatment (extraction, ultra-filtration, ion-exchange materials, etc.), catalysis, separation, etc. As an industrial and commercial product, PVA is valued for its solubility and biodegradability, which contributes to its very low environmental impact. Several microorganisms ubiquitous in artificial and natural environments — such as septic systems, landfills, compost and soil — have been identified and they are able to degrade PVA through enzymatic processes. Membranes have gained an important place in chemical technology and are used in a broad range of applications. The key property that is exploited is the ability of a membrane to

Poly(Vinyl Alcohol)[PVA]-Based Polymer Membranes…

107

control the permeation rate of a chemical species through the membrane. In controlled drug delivery, the goal is to moderate the permeation rate of a drug from a reservoir to the body. In separation applications, the goal is to allow one component of a mixture to permeate the membrane freely, while hindering permeation of other components. The objective of this chapter is to give an overview of the developments in synthesis and applications of PVA-based membranes in the last years.

2. SEPARATIONS BY MEMBRANAR PROCESSES 2.1. Pervaporation Processes Pervaporation, in its simplest form, is an energy efficient combination of membrane permeation and evaporation. Pervaporation involves the separation of two or more components across a membrane by differing rates of diffusion through a thin polymer and an evaporative phase change comparable to a simple flash step. A concentrate and vapour pressure gradient is used to allow one component to preferentially permeate across the membrane. A vacuum applied to the permeate side is coupled with the immediate condensation of the permeated vapors. Pervaporation is typically suited to separating a minor component of a liquid mixture, thus high selectivity through the membrane is essential. Despite concentrated efforts to innovate polymer type and tailor polymer structure to improve separation properties, current polymeric membrane materials commonly suffer from the inherent drawback of tradeoff effect between permeability and selectivity, which means that membranes more permeable are generally less selective and vice versa. Pervaporation (PV) is considered to be a promising alternative to conventional energy intensive technologies like extractive or azeotropic distillation in liquid mixtures’ separation for being economical, safe and ecofriendly. PV can be considered the so-called ‘clean technology’, especially well-suited for the treatment of volatile organic compounds. The separation of compounds using pervaporation methods can be classified into three major fields viz. (i) dehydration of aqueous–organic mixtures [12], (ii) removal of trace volatile organic compounds from aqueous solution [13] and (iii) separation of organic–organic solvent mixtures [14]. The hydrophilic membranes were the first ones to have found an industrial application for organic solvent dehydration by PV [15]. Very recently, B. Smita et al. [16] reported that some restrictions for a variety of membranes for their application are still encountered, suggesting potential routes to overcome these drawbacks as, for example, the development of appropriate membrane material (flux and selectivity of a membrane are deciding factors in pervaporation mass transport; therefore, development of a new polymer material is a key research area in membrane technology. The aim in the development of new pervaporation membranes is either to increase the flux, keeping the selectivity constant or aiming for higher selectivities at constant flux, or both. In order to achieve such goals, the use of PVA as component of copolymers, blends, or composites membranes for pervaporation has been used.

108

Silvia Patachia, Artur J. M. Valente, Adina Papancea et al.

2.1.1. Pervaporation of Phenol/Water Using pervaporation through PVA membranes, J. W. Rhim et al. [17] have studied the separation of water-phenol mixtures. The pervaporation separation of water-phenol mixtures was carried out using poly(vinyl alcohol) (PVA) cross-linked membranes with low molecular weight poly(acrylic acid) (PAA), at 30, 40, and 50 °C. They have used pervaporation because the separation rate is higher (for liquid organic mixtures) in pervaporation than in reverse osmosis. A separation factor of the mixture, α, is calculated using α = ( Ywater / Yphenol ) / (Xwater / Xphenol ) where X is the weight fraction of permeate and Y, the weight fraction of feed. A very high separation factor has been obtained in phenol dehydration by using pervaporation process and PVA/PAA as membranes. The membrane composition and the process characteristics are presented in table 1. Table 1. Characteristics of the separation process by pervaporation function of the membrane composition and structure, composition of feed mixture and temperature [18] Membrane composition PVA/PAA 80/20

Composition of liquid mixture phenol/water

80/20

Permeation rate / / (g m-2 h-1)

T / ºC

Separation factor

50

30

3580*

* Ref. 17.

Conclusion: the separation factor increases by increasing the cross-linker, and decreases by increasing the temperature.

2.1.2. Isopropanol/Water Separation The selective separation of water from aqueous solutions of isopropanol or the dehydration of isopropanol can be carried out with different membranes, which contain polar groups, either in the backbone or as pendent moieties. For the dehydration of such a mixture, poly(vinyl alcohol) (PVA) and PVA-based membranes have been used extensively. PVA is the primary material from which the commercial membranes are fabricated and has been studied intensively for pervaporation because of its excellent film forming, high hydrophilicity due to –OH groups as pendant moieties, and chemical-resistant properties. On the contrary, PVA has poor stability at higher water concentrations, and hence selectivity decreases remarkably. The use of conjugated polymer as membranes to separate various liquid mixtures has been reported in the literature [19,20]. From those, polyaniline (PANi) is one of the most interesting and studied conjugated polymers. Polyaniline is usually prepared by direct oxidative polymerization of aniline in the presence of a chemical oxidant, or by electrochemical polymerization on different electrode materials [21,22]. The possible interconversions between different oxidation states and protonated and depronated states [23], figure 4, make this material remarkable for different purposes. Under most conditions, PANi

Poly(Vinyl Alcohol)[PVA]-Based Polymer Membranes…

109

acts as a passive material, but electrolysis or exposure to acidic aqueous solutions gives rise to conductive materials. In fact, the susceptibility of PANi protonation-deprotonation is an important property once it makes possible to control the electrical conductivity of polyaniline, being possible to obtain changes of more than two orders of magnitude in the electrical conductivity [24]. Both synthesis and characterization of PANi have been reviewed by different authors [21-23]. These reviews deal with chemical, electrochemical and gas-phase preparations, polymerization mechanisms, physicochemical and electrochemical properties, redox mechanisms, theoretical studies, and applications of the polymer. Interest in polyaniline (PANi), as a material for membrane separations, stems for its high selectivity toward liquids since most liquids are in the size regime of 0.2–1 nm. Another advantage is that PANi has the ability to be tailored after its synthesis through doping/undoping processes. Since there is a tremendous driving force for adding protonic dopants to the imine nitrogens in the PANi backbone [20], the polymer chains are readily pushed apart by the incoming dopants. Thus, doping would induce morphological changes in the polymer resulting in varying permselectivities. Besides such morphological changes, the undoped and doped forms of PANi exhibit different characteristics. For instance, the undoped form of PANI is hydrophobic, while the doped form is hydrophilic [25,26]. Hence, doped PANi preferentially permeates water over the organics, such as isopropanol. The abovementioned advantages are considered to search for novel membranes containing PANi nanoparticles dispersed in the PVA matrix. The synthesis of a novel hybrid nanocomposite membrane by in situ polymerization of aniline in the PVA matrix in acidic media is described in the Ref. 27. Aniline monomer was introduced into the PVA matrix and by carrying in situ polymerization outside the mesopores of the polymer matrix, a nanocomposite structure was formed. The organic phase extends along the channels to the openings in the nanocomposite structure due to strong interactions between the nanoparticle formed and the continuously polymerized PANi nanoparticles. This hybrid polymer shows lower swelling degree and higher water selectivity (about five-folds) compared to the plain poly(vinyl alcohol). M. Sairam et al. [28], taking on the basis of the cited PANi nanoparticles dispersed in the PVA matrix, suggests the incorporation of TiO2 filler-coated with polyaniline (emeraldine state) salt nanoparticles in PVA. PVA contains a large number of hydroxyl groups which can effectively inhibit the aggregation of TiO2 nanoparticles by the organic surface modification and help to keep the TiO2 particles well dispersed in the aqueous PVA solution at the nanoscale for dehydration of iso-propanol. In order to control the dispersion of TiO2 fillers and to adjust the permselectivity, the PV membranes formed have been crosslinked chemically with glutaraldehyde. With this modification of TiO2 nanoparticles, it is expected that strong interfacial bond, viz., Ti–O–C be formed on the surface of TiO2 nanoparticle, anchors PVA molecules to the surface of TiO2 nanoparticles such that surfaces of TiO2 nanoparticles will be wrapped with the layer of PVA polymer. It is known [29] that there are number of Ti–OH groups that will cover the surface regions of TiO2 nanoparticles. When PVA chain segments are adsorbed onto the surface of TiO2 nanoparticle, Ti–OH groups on the surface of TiO2 nanoparticles will react with the hydroxyl groups linking to the PVA chains. Dehydration and condensation reactions can occur between both the hydroxyl groups.

NH

N HN

HN

reduction

NH

N

N

XNH NH

N

N

Figure 4. Interconversions among the various intrinsic oxidation states and protonated/deprotonated states in polyaniline.

NH

1st acid-base cycle

reduction

oxidation HN

as-cast EM film

NH

solvent (NMP)

X-

(EM)

N

base (NaOH)

N

(H+X-)

HN

acid

4H+ + 2e-

(PNA)

HN N

N

(NA)

(LM)

Poly(Vinyl Alcohol)[PVA]-Based Polymer Membranes…

111

Another approach to enhance separation performance of membrane for dehydration of isopropanol is the modification of PVA membranes in gaseous plasma [30]. The modification of membrane properties in nitrogen plasma environment lead to increase in selectivity by about 1477 at 25 °C; such increase in the selectivity is justified by an increase of crosslinking on membrane surface provoked by plasma treatment. The same authors reported the possibilities of using a membrane made by PVA modified by LiCl, whose surface has been modified by exposure to low-pressure nitrogen plasma [31]. The best results have been obtained for 0.05 wt% of LiCl in PVA membrane at 25 ºC (selectivity 14 and flux 250 g m-2h-1). Hybrid membranes composed of poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS), synthetised via hydrolysis and a co-condensation reaction for the pervaporation separation of water-isopropanol mixtures has also been reported [32]. These hybrid membranes show a significant improvement in the membrane performance for water– isopropanol mixture separation. The separation factor increased drastically upon increasing the crosslinking (TEOS) density due to a reduction of free volume and increased chain stiffness. However, the separation factor decreased drastically when PVA was crosslinked with the highest amount of TEOS (mass ratio of TEOS to PVA is 2:1). The highest separation selectivity is found to be 900 for PVA:TEOS (1.5:1 w/w) at 30°C. For all membranes, the selectivity decreased drastically up to 20 mass % of water in the feed and then remained almost constant beyond 20 mass %, signifying that the separation selectivity is much influenced at lower composition of water in the feed. Recently, a new effective membrane for different organic solvents dehydration by pervaporation has been reported. Novel hydrophylic polymer membranes based on crosslinked poly(allylamine hydrochloride) (PAA.HCl)-PVA have been developed [33]. The crosslinking agent was GA. The role of the PVA into the membrane is to increase its flexibility and the stability. But the increasing of the PVA ratio, determines the decreasing of the water selective amine hydrochloride functional groups amount and as consequence, the rate of water intake by the membrane decreases. So, for different specific applications the optimization of the PAA.HCl/PVA ratio in the formulation is essential. Also, the amount of GA and curing temperature has to be optimized to obtain the desired membrane properties. The characteristics of the iso-propanol (IPA) dehydration process, by using the pervaporation technique, are presented in the table 2. Table 2. The characteristics of the iso-propanol (IPA) dehydration process, by using pervaporation technique, through (PAA.HCl)-PVA membrane Composition of the membrane PAA.HCl/PVA/GA 60/35/5

* Ref. 33.

Composition of liquid mixture IPA-water (wt%)

85/15

Water flux / / (kgm-2h-1)

T / ºC

Separation factor

3.14

70

2930

112

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

2.1.3. Pervaporation Ethanol/Water Alcohol is a clean energy source that can be produced by the fermentation of biomass. However, it needs to be highly concentrated. In general, aqueous alcohol solutions are concentrated by distillation, but an azeotrope (96.5 wt% ethanol) prevents further separated by distillation. Pervaporation, a membrane separation technique, can be used for separation of these azeotropes: pervaporation is a promising membrane technique for the separation of organic liquid mixtures such as azeotropic mixtures [34] or close-boiling point mixtures. The synthesis of novel organic-inorganic hybrid membranes via hybridization between organic and inorganic materials using the sol-gel reaction is reported elsewhere [35]. It is well-known that poly(vinyl alcohol) (PVA) membranes are highly water permselective for aqueous ethanol solutions during PV. However, the swelling of the PVA membrane in an aqueous ethanol solution results in both an increase in solubility and diffusivity of ethanol, and consequently lowers the water permselectivity [36]. The control of membrane swelling has been attempted by cross-linking, surface modification, and annealing methods. However, it is difficult to effectively control the swelling of the membrane. An attempt to improve and to control the swelling is done by using mixtures of PVA and tetraethoxysilane (TEOS), as an inorganic component, in order to obtain PVA/TEOS hybrid membranes prepared by sol-gel reaction. The addition of TEOS into the PVA membrane decreases the swelling of the membrane and improves the water permselectivity of the PVA/TEOS hybrid membrane. T. Uragami et al. also studied the effect of the annealing process to PVA/TEOS hybrid membranes. They found that the separation factor H2O/EtOH increases from 329 to 893 (with the same permeation rate) when PVA/TEOS (TEOS content 25 %) membranes are submitted from an annealing process at 160 ºC during 8 hours to 130 ºC during 24 hours. In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity–hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer; the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H2O wt% in the pervaporate in the range 83–92 and a water selectivity, αH2O , of 250 at 25 ºC) is higher than that of the non-treated one (αH2O = 19) as well as that of the acrylic acid treated membrane (αH2O = 22). PVA dense membranes treated by acrylic acid (Acr.Ac) plasma were obtained by A. Essamri et al. [38]. These membranes were used for dehydration of the EtOH-H2O mixtures by pervaporation. The behaviour of these films on ethanol-water pervaporation has increased performances after plasma treatment. This means an increase of the flux (J) and water selectivity (β) for the modified membrane – due to the surface properties modification by plasma treatment – comparing to the untreated membrane. Conclusion: using plasma treatment, a good ratio between flux and selectivity could be obtained. Also, different other techniques for obtaining PVA/PAcr.Ac blends were reported [3956]:

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

113

1. mixing of PVA and PAcr.Ac. aqueous solutions, solvent evaporation and thermal treatment of the resulted film; 2. mixing of PVA and PAcr.Ac. aqueous solutions with curing agents solutions, solvent casting and thermal treatment of the resulted film; 3. repetitive cycles of freezing and thawing of the aqueous solutions of polymer mixture, in the presence or the absence of the curing initiators; 4. UV irradiation either of the aqueous solutions of polymers mixtures in the presence of photoinitiators and curing agents, or of the PVA hydrogels swelled with acrylic acid; 5. acrylic acid polymerization in the matrix of PVA, in the presence of curing agents and initiators; 6. sedimentation polymerization of acrylic acid in the presence of PVA solution, crosslinking agent and initiator; 7. swelling of PAcr.Ac dried hydrogels with an aqueous solution of PVA and application of the freezing and thawing technique. Changes in blends’ properties were obtained through different ways: by changing the polymer mixing ratios; by using a small amount of acids that are catalysts for esterification reactions; by changing the crosslinking degree of the polymers. PVA and PAcr.Ac. are compatible polymers on the whole range of composition [40-45]. These blends are homogeneous and the films are transparent evidencing a good clarity [43,57] or semitransparency [43]. However a heterogeneous IPN [45] was obtained by acrylic acid polymerization in a PVA matrix. The blends could exhibit different morphologies: continuous or microporous [46]. The blend crystalinity degree decreases with increasing the PAcr.Ac content up to 50 wt%, from 26 % to 2 %, and then remains constant [42]. The blends are water insoluble [47]. They can swell in different solvents: water, acetone, aqueous solutions of acids and alkalis [47]. The swelling ratios increase with increasing the PAcr.Ac content in IPNs [45,48]. It was pointed out that the swelling degree evidenced a strongly decrease as the PAcr.Ac content in membrane decreases to 20% [49]. The technique of obtaining blends influences their swelling ratios by inducing different crosslinking degrees. For example, increasing the number of freezing-thawing cycles leads to a swelling ratio significant decrease [50]. In general, the swelling ratios increase with the increasing the temperature up to 40 ºC [45]. The dependence of swelling ratios on temperature shows a different function of the blend composition. So, interpenetrating polymer networks (IPNs) with a weight ratio of vinyl alcohol residue in PVA to acrylic acid monomer 4:6 exhibit positive swelling changes with temperature but IPNs 6:4 evidence negative swelling ones [48]. pH strongly influences the swelling behavior of the blends. For example, the difference of the swelling ratio of IPN 4:6 between pH=4 and pH=7 is 2.0 [48]. Membranes of PVA/PAcr.Ac blends evidence a selective permeability against different components of a liquid mixture. So, they may be used for the ethanol dehydration by pervaporation technique. Table 3 presents a summary of the published results.

114

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

These blends show good mechanical properties. The presence of PVA in the blend improves the mechanical properties. Hydrogels have a significant mechanical strength and elasticity [42]. The tensile strengths are larger than those of crosslinked PVA membranes and show a maximum value at about 0.7 wt% glutaric dialdehyde (GA) [46]. Full-IPNs have higher compressional strength (2929 g load for 50 % compression) than the corresponding semi-IPNs (1883 g load for 50 % compression) [42]. These membranes can swell in water and different aqueous solutions evidencing the following aspects: • • •

the presence of PAAm affects in a positive way the swelling; the swelling in water increases with temperature (positive thermosensitivity); -swelling in the water/ethanol mixture increases linearly with the water content.

Because of membrane preferential swelling in different aqueous solutions, it may be recommended for use in separation processes by pervaporation. The PVA/PAAm IPN membranes were found to have pervaporation separation factors ranging from 45 to 4100 and permeation rates of about 0.06-0.1 kg m-2 h-1, for 95 % ethanol aqueous solution, at 75 ºC [46]. For a concentration of 10 wt% ethanol, the permeation rates were as large as 9 kg m-2 h-1 and the separation factors were about 20 [46]. Recently, a new effective membrane for dehydration of different organic solvents by pervaporation has been reported. Novel hydrophylic polymer membranes based on crosslinked poly(allylamine hydrochloride) (PAA.HCl)-PVA have been developed [33]. The crosslinking agent was glutaraldehyde (GA). The role of PVA into the membrane is to increase its flexibility and the stability. But the increasing of PVA percentage, determines the decreasing of the water selective aminehydrochloride functional groups amount and as consequence, the rate of water intake by the membrane decreases. So, for different specific applications, the optimization of the PAA.HCl/PVA ratio in the formulation is essential. Also, the amount of GA and curing temperature has to be optimized to obtain the desired membrane properties. The characteristics of the ethanol dehydration process, by the pervaporation technique, are presented in table 4. Polymers, such as polysaccharides (cellulose and chitosan (CS)) show a stronger affinity to water; hence their copolymers, blends or composites have been widely investigated for pervaporative (PV) separation of EtOH/H2O mixtures [58-60]. Chitosan is generally preferred due to its high abundance, natural occurrence, hydrophilicity, chemical resistance, adequate mechanical strength, good membrane forming properties and ease of processing. PV performance of EtOH/H2O mixtures through the surface crosslinked CS composite membranes exhibit a high selectivity value but a low permeation flux [61]. The PV membranes of derivatives of CS obtained by chemical modification have also been widely studied [62,63].

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

115

Table 3. Characteristics of the separation process by pervaporation function of the membrane composition and structure, composition of feed mixture and temperature [18,43,46] Composition of the membrane PVA/PAcr.Ac 50/50 IPN 30/70 IPN 50/50 IPN 70/30 IPN 90/10 IPN 80/20

Composition of liquid mixture ethanol-water 95.6/4.4 10/90 85/15 10/90 85/15 10/90 85/15 10/90 85/15 95.6/4.4 90/10 80/20 50/50

95/5

Permeation rate / / (g m-2 h-1)

T/ ºC

Separation factor

260

50

5000 750 3800 360 2700 110 2000 90 9 30 27 60 65 125 120 550

50

50 12 0.8 15 0.85 15 1.0 18 3.0 39 14000 5800 9000 2800 1500

50 50 50 60 75 60 75 60 75 75 60

Permeate activation energy Ea / (kJ mol-1) -

30.5 30.9 38.9 -

260 150

Table 4. Dehydration of ethanol, using membranes PAA.HCl (60 wt%)–PVA (35 wt%–GA (5 wt%) (aprox. 60μm thick) [33] Feed concentration / (wt%)

T / ºC

Water flux / (kg m-2 h-1)

Selectivity

85

70

2.00

450

95

70

0.47

3953

B.-B. Li et al. [64] have studied the separation of EtOH-H2O solutions by pervaporation (PV) using chitosan (CS), poly (vinyl alcohol)-poly(acrylonitrile) (PVA–PAN) and chitosanpoly(vinyl alcohol)/poly(acrylonitrile) (CS–PVA/PAN) composite membranes. It was found that the separation factor of the CS–PVA/PAN composite membrane increased with an increase of PVA concentration in the CS–PVA polymer from 0 to 40 wt%. With an increase in the membrane thickness from 12 to 18 µm, the separation factor of the CS–PVA/PAN composite membrane increased and the permeation flux decreased. With an increase of ethanol–water solution temperature, the separation factor of the CS membrane decreased and the permeation flux of the CS membrane increased while the separation factor and the permeation flux of PVA/PAN and CS–PVA/PAN composite membranes increased.

116

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

Sodium alginate (SA), which is one of the polysaccharides extracted from seaweed, has shown excellent water solubility [65], but the mechanical weakness of SA membranes has been a drawback as a pervaporation membrane material. The use of SA–PVA blended membranes prepared by physical mixing of components, in different ratios, for pervaporation dehydration is reported elsewhere [66,67]. Taking on the basis of SA-PVA membranes, Dong et al. [68] studied the PVA–SA hollow-fiber composite membranes for organic dehydration by pervaporation. In particular, a polysulfone hollow-fiber membrane is coated by a PVA-SA blended solution. The founded optimal process of preparing membranes is as follows: 80 wt% PVA and 20 wt % SA are blended, and the casting solution of the PVA–SA blend with a concentration of 2 wt % is obtained by dissolving the blend in water; then the blend solution is cast onto the PS hollow-fiber membrane, and the composite membrane is crosslinked with 1.5 wt% maleic acid and 0.05 wt% H2SO4 in ethanol solvent for 8 h. For isoproanol, n-butanol, tert-butanol and ethanol aqueous solutions, as the alcohol concentration is 90 wt% at 45 ºC, higher separation factors and permeation fluxes of crosslinked PVA–SA blended membranes are obtained: 1727, 414 g m-2 h-1; 606, 585 g m-2 h-1; 725, 370 g m-2 h-1 and 384, 384 g m-2 h-1, respectively. This shows that these blended membranes have the potential to be used in industry. 2.1.7. Acetic Acid/Water Separation by Pervaporation Poly(vinyl alcohol) and polyacrylamide (PAAM) blends, obtained by the different methods described above, can also be used for acetic acid dehydration, due to its capacity to swell in mixtures of acetic acid/water. Swelling in water/acetic acid mixture shows a maximum of swelling shifting to higher temperatures when higher acetic acid concentrations increase (from 20 ºC for 50 % acetic acid to 40 ºC for 70 %). Water is preferentially sorbed by membranes, but much less from water-acetic acid mixtures than from ethanol/water mixtures [46]. Table 5 presents the characteristics of the pervaporation process. Table 5. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18,52] Compositi-on of the membrane PVA/PAcr.Ac

Composition of liquid mixture

Permeation rate / / (g m-2 h-1)

T / ºC

Separation factor

75/25

Acetic acidwater

5.6

30

795

90/10

A recent paper [69] presents a new type of PVA hybrid membrane prepared by hydrolysis followed by condensation of a PVA and a tetraethylorthosilicate (TEOS) mixture, which shows a significant performace in water-acetic acid mixture separation. The highest separation selectivity (1116) with a flux of 3.33×10-2 kg m-2 h-1 at 30 ºC for 10% mass of water in the feed has ben obtained by using the membrane containing 1:2 mass ratio of PVA and TEOS. The performance of these membranes was explained on the basis of a reduction of free volume and a decrease of the hydrophylic character owning to the formation of

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

117

covalently bonded crosslinks. Significant lower apparent activation energy values have been obtained for water permeation comparatively to these of acetic acid permeation. The close values obtained for activation energy for total permeation and water permeation signify that the coupled transport is minimal due to the selective nature of membranes. The equal magnitude of activation energy for water permeation and activation energy for water diffusion indicates that both diffusion and permeation contribute almost equally to the PV process. The Langmuir mode of sorption dominates the process for all types of studied membranes. Another recent work presents the possibility to use a membrane made by PVA-gacrylonitrile (AN) to separate acetic acid/water mixtures by pervaporation [70]. The best separation factor (14.6) has been obtained by using PVA-g-AN (52 %) membrane, at 30ºC, 90 % acetic acid in the feed. The permeation rate was 0.09 kg m-2 h-1.

2.1.5. Separation Caprolactam (CPL)/Water Mixtures by Pervaporation Caprolactam (CPL) is the monomer of Nylon-6, extensively used in high quality Nylon-6 fibers and resin obtaining. Worldwild capacities reached above 4.5 million metric tones in 2005. A CPL dehydration study has been performed by pervaporation, using PVA crosslinked membranes (with GA as crosslinker agent and heat treatment of the membrane) [71]. In spite of the excellent dehydration performance for CPL/water mixtures exhibited by PVA crosslinked membranes (total permeation flux by 800 g m-2 h-1 and separation factor by 575, for PVA membrane crosslinked with 0.5 wt% GA, at 323 K and 50 wt% CPL in the feed), the authors recommended the use of a composite membrane with an active layer made by PVA, due to the poor durability and mechanical strength of the studied membrane. 2.1.6. Separation of Fluoroethanol/Water Mixtures by Pervaporation 2,2,2,-trifluoroalcohol (TFEA) is used for obtaining 2,2,2-trifluoroethyl methacrylate (TFEMA), necessary for preparation of functional water repellent paints and optical fiber coating agents. TFEMA can be manufactured by esterification of TFEA and methacrylic acid (MA) in the presence of an acid catalyst, at 70 ºC. To obtain a higher conversion rate it is necessary to remove the water from the system, avoiding the formation of the thermodynamic equillibrium composition. To attain this goal, a pervaporation technique has been proposed, using a PVA composite membrane, made by casting of a mixture of PVA aqueous solution and a GA one on a polyethersulfone (PES) porous support, solvent evaporation and thermic curing [72]. Excellent dehydration performance has been obtained (separation factor 320 and permeation flux 1.5 kg m-2 h-1, for 90 wt% TFEA in the feed and 80 ºC). 2.1.7. Separation of Methacrylic Acid/Water Mixtures by Pervaporation A PVA composite membrane, made by casting of a mixture of PVA aqueous solution and a GA one on a polyethersulfone (PES) porous support, solvent evaporation and thermic curing, has been used to attain this aim [72]. Excellent dehydration performance has been obtained (separation factor 740 and permeation flux 2.3 kg m-2 h-1, for 90 wt% TFEA in the feed, and 80 ºC). 2.1.8. Water Desalination PVA/Poly(ethylene glycol) (PEG) membranes crosslinked by aldehydes and sodium salts were used in water desalination by pervaporation. The desalination of 8 % NaCl solution by

118

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

pervaporation at 55 ºC and 5.00 kPa (downstream pressure) resulted in a single stage salt rejection of 99% and the water flux of 14 kg h-1 [73].

2.1.9. Dehydration of Methanol by Pervaporation Another important application of membrane-based pervaporation is a well-established and commercially exploited method for the dehydration of organic solvents; in particular the dehydration of alcohols is done with the help of high permselective (hydrophilic) poly(vinyl alcohol)/polyacrylonitrile (PVA/PAN) thin film composite membranes, under the trade name of “GFT- Gesellshaft Fur Trenntechnik” membranes. One of the key successes of PV is that, if suitable membranes can be produced with a high permeability and a good selectivity to water, it is possible to achieve an excellent separation, particularly at the azeotropic composition. However, more number of novel polymeric membranes are needed for a successful operation of the process in view of the fact that PV is environmentally cleaner than the conventional distillation; moreover, this process is energy intensive. Consequently the success of any membrane depends on a high flux, a good separation factor (selectivity) and a long-term stability as well as a favourable mechanical strength to withstand the cyclic modes of PV operating conditions, as described before. Also, membranes from blends of PVA/Poly(acrylic acid) [PAcr.Ac.] show a selective permeability against different components of a liquid mixture. This property of membranes makes them useful for the separation of components from liquid mixtures by the pervaporation method, i.e., for methanol dehydration. Recently, a novel hydrophylic polymer membrane based on poly(allylamine hydrochloride) (PAA.HCl)/PVA, crosslinked with GA, has been also tested for methanol dehydration by pervaporation technique [33]. Even if the reported results show a small selectivity of the last type of membrane, the blend’s composition, the curing degree and the process conditions (temperature, feed concentration, etc.) could be used to obtain a better separation of methanol. Table 6 presents a summary of the published results. Table 6. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18] Composition of the membrane

Composition of liquid mixture

PVA/PAcr.Ac: 80/20

Methanolwater

PAA.HCl/PVA/ GA 60/35/5

Methanolwater (%wt.)

70/30 90/10 95/5 86.5/1 3.5

Permeation rate / / (g m-2 h-1) 70 340 109 33 1800

T / ºC

Separation factor

Ref.

50 70 70 70 60

55 28 465 2650 23

42

33

2.1.10. Dehydration of Acetone by Pervaporation Novel hydrophilic polymer membranes based on crosslinked poly(allylamine hydrochloride) (PAA.HCl)-PVA have been developed in order to dehydrate different organic compounds by pervaporation [33]. The characteristics of the acetone dehydration process,

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

119

using a pervaporation technique, are presented in the table 7. The high selectivity of the membrane should be noted. The selectivity and flux characteristics of these membranes are excellent compared with most of the known membranes. Table 7. Dehydration of acetone, using membranes PAA.HCl (60%wt.)-PVA (35%wt.-GA(5%wt.) (aprox. 60μm thick) [33] Feed concentration / (% wt.) 86

T / ºC 50

Water flux / (kg m-2 h-1) 1.80

Selectivity 2270

2.1.11. Pervaporation of Ethanol/Toluene PVA-PAcr.Ac. membranes have been tested also for ethanol separation from ethanol/toluene mixture, by using pervaporation technique. The reported data concerning the separation process characteristics are presented in table 8. Table 8. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18, 40] Composition of the membrane PVA/PAcr.Ac 10/90

Composition of liquid mixture Ethanol/toluene

Permeation rate / / (g m-2 h-1)

T / ºC

Separation factor

25-480

30

300-80

10-90% ethanol

2.1.12. Pervaporation of Ethanol/Benzene PVA-PAcr.Ac.blends membranes are suitable also for separation of components in ethanol/benzene mixtures. Reported data are presented in table 9. 2.1.13. Pervaporation of Methanol/Toluene Methanol/toluene mixtures could be separated by pervaporation technique using PVA/PAcr.Ac. blend membranes. Reported data are presented in table 10. Table 9. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18,46] Composition of the membrane PVA/PAcr.Ac

Composition of liquid mixture ethanol/benzene

Permeation rate/ / (g m-2 h-1)

T / ºC

Separation factor

Permeate activation energy Ea / (kJ mol-1)

20/80

10/90

30

50

110

19.2

SIPN

90/10

560

30/70

10/90

12

SIPN

90/10

460

30/70

10/90

6

SIPN

90/10

360

3.5 50

650

27.6

1.9 50

1100 53

31.4

120

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al. Table 10. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18,40] Composition of the membrane PVA/PAcr.Ac 10/90

Composition of liquid mixture methanol/toluene 10/90 30/70

Permeation rate/ / (g m-2 h-1)

T / ºC

Separation factor

120 265

30 30

460 50

2.1.14. Separation Methyltertbutyl Ether (MTBE)/Methanol Mixtures by Pervaporation MTBE is a well known enhancer of the number of octanes in gasoline and as excellent oxygentated fuel additives that decrease carbon monoxide emissions. Therefore, MTBE has been one of the fastest growing chemicals of the past decade. MTBE is produced by reacting methanol with isobutylene from mixed-C4 stream liquid phase over a strong acid ionexchange resin as catalyst. An excess of methanol is used in order to improve the reaction conversion. This excess has to be separated from the final product. The pervaporation technique, more energy efficient and with lower cost process, has been proposed as alternative to distillation [74]. A membrane prepared by PVA blending with PAcr.Ac. in aqueous solution, casting, solvent evaporation and then crosslinking by heat treatment (at 150 ºC), has been used. The obtained results show that the prepared membranes are methanol selective, but the performance of these membranes (separation factor=30, for PVA/Pacr.Ac.=80/20, 5 wt% methanol in the feed, 25 ºC) is lower than those reported by J.W. Rhim and Y.K. Kim [75] (separation factor 1250 for PVA/Pacr.Ac.=75/25, 20 wt% methanol in the feed, 30 ºC). The authors suggested that a combination of pervaporation with a conventional separation technique such as a hybrid distillation-pervaporation system could be useful economically to break the azeotropy. 2.1.15. Pervaporation of Benzene/Cyclohexane The separation of benzene/cyclohexane mixtures is one of the most important and most difficult processes. Cyclohexane is produced by catalytic hydrogenation of benzene. The unreacted benzene in the effluent stream must be removed for pure cyclohexane recovery. Separation of benzene and cyclohexane is difficult because they have close boiling points (difference only 0.6 K) and close molecular sizes [76]. It is generally thought that separating benzene/cyclohexane mixtures is mainly governed by solubility selectivity due to the interaction between benzene molecule and membrane. Hence, increasing benzene solubility in the membrane is essential to obtain high permselectivity toward benzene. Poly(vinyl alcohol) (PVA) is polar and hydrophilic, and is an ideal membrane material to separate benzene/cyclohexane mixtures [77]. The selection of PVA is also due to its economical cost, commercial availability and good membrane-forming properties. F. Peng et al. report [78] the synthesis of poly(vinyl alcohol) membranes incorporating crystalline flake graphite (CG-PVA membranes). These blends take advantage of structure of graphite being similar to that of benzene favouring, in this way, the adsorption and packing of benzene on graphite surface and, consequently, increase the selectivity. A CG-PVA membrane exhibits a higher

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

121

separation factor of 100.1 with a flux of 90.7 g m-2 h-1 at 323 K for benzene/cyclohexane (50/50, w/w) mixtures, showing that the incorporation of graphite into the PVA matrix interfered the polymer chain packing and enhanced effectively fractional free volume, and thus favourable for components diffusing through the membrane. Another interesting approach reported by the some authors [79] is to perform pervaporation of benzene/cyclohexane by using β-cyclodextrin (β-CD)-filled cross-linked poly(vinyl alcohol) (PVA) membranes (β-CD/PVA/GA). In the present case, the very important properties of the β-CD are used to increase the perselectivity toward benzene. The permeation flux of βCD/PVA/GA membranes increased when the β-CD content was 0–8 wt%, but permeation flux decreased slightly when the β-CD content was 8–20 wt%. The separation factor towards benzene increased when β-CD content was in the range 0–10 wt% and decreased slightly when the β-CD content was 10–20 wt%. Compared with the β-CDfree PVA/GA membrane, the separation factor of the β-CD/PVA/GA membrane for benzene to cyclohexane considerably increased from 16.7 to 27.0, and the permeation flux of benzene increased from 23.1 to 30.9 g m-2 h-1 for benzene/cyclohexane (50/50, wt) mixtures at 323 K. To solve the tradeoff between permeability and selectivity of polymeric membranes, organic-inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and -glycidyl oxypropyl trimethoxysilane (GPTMS) were prepared by an in situ sol-gel approach for pervaporative separation of benzene/ cyclohexane mixtures [80]. The permeation flux of benzene increased from 20.3 g m-2 h-1 for pure PVA membrane to 137.1 g m-2 h-1 for PVAGPTMS membrane with 28 wt % GPTMS content, while the separation factor increased from 9.6 to 46.9, simultaneously. The enhanced and unusual pervaporation properties were attributed to the increase in the size and number of both network pores and aggregate pores, and the elongation of the length of the diffusion path in PVA-GPTMS hybrid membranes. Another hybrid membrane was prepared by filling carbon graphite (CG) into poly (vinyl alcohol) (PVA) and chitosan (CS) blending mixture [81]. This blend membrane shows homogenous distribution of graphite particles, considerable alteration of hydrogen bonding interaction, remarkable decrease of crystallinity degree, dramatic enhancement of mechanical properties and significant increase of free volume in CG-PVA/CS, which may contribute for improving the separation performance of the membranes by the synergistic effect of blending and filling. Comparing the performance of this blend with that used for PVA and PVA/chitosan membranes, for C6H6/C6H12 separation, that new hybrid membrane exhibits a highest separation factor of 59.8 with a permeation flux of 124.2 g m-2 h-1 at 323 K, 1 kPa.

2.1.17. Separation Cyclohexene/Cyclohexan Mixtures by Pervaporation Solid PVA-Co2+ composite asymetric membranes have been prepared starting from PVA and two different salts: Co(NO3)2 and Co(CH3COO)2, respectively, in order to separate cyclohexene/cyclohexan mixtures. A facititated transport mechanism has been evidenced, due to the capacity of Co2+ ions to coordinate the olefin molecules [82]. The authors reported stronger complexation of Co2+ ions with cyclohexene in the case of PVA/ Co(CH3COO)2 mixtures then in the case of PVA/ Co(NO3)2 mixtures. It was found that for a concentration ratio of ([Co2+]/[OH]) by 0.75 mol/mol, the permeation flux of PVA membrane containing Co2+ increases 2-3 times and the separation factor increses 50 times compared with pure PVA membrane.

122

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

2.1.17. Fusel Oil Components Separation One of the main products of sugar manufacturing is molasses, which contains approximately 50% sucrose and 50% other components (water, various other organic components and inorganic salts). Because of its high sucrose content, a substantial portion of the molasses is used for the production of ethyl alcohol through fermentation. The byproducts of the fermentation broths, more volatile than the alcohol, are mainly aldehydes with acetaldehyde being the principal component. The aldehyde is removed, as a distillation head product. The other by-product of the distillation step, the bottom product, is fusel oil. It is composed of several alcohols, primarily C3, C4 and C5 aliphatic alcohols. The separation of its components, using pervaporation technique and PVA/PAcr.Ac. blend as membrane has been reported [55]. The characteristics of the pervaporation process are presented in table 11. Table 11. Characteristics of the separation process by pervaporation according to membrane composition and structure, composition of feed mixture and temperature [18,55] Composition of the membrane PVA/PAcr.Ac 90/10

Composition of liquid mixture: fusel oil

Permeation rate/ / (g m-2 h-1)

T / ºC

Separation factor

5000

60

10

Alcohols mixture with 10-30 % of water

Permeate activation energy Ea / (kJ mol-1) 49.4-41.7 (water) 60.8-55.7 (EtOH)

2.2. Separation by Evapomeation Evapomeation is a new membrane-separation technique for liquids mixtures, which eliminates some disadvantages of the pervaporation technique such as the decreasing of membrane permselectivity, due to its swelling by the direct contact with the feed solution. In evapomeation technique the membrane is not in direct contact with the feed solution, only with the solution’s vapors. In this way the swelling of the membrane could be suppressed and consequently, the permeation rates in evapomeation are smaller than those in pervaporation, but the separation factor is greater [83]. The differences between the pervaporation and evapomeation processes may be seen in figure 5.

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

123

Figure 5. Schematic presentation of the pervaporation and evapomeation processes.

2.2.1. Isomers Separation by Evapomeation Separation of n-propanol from a mixture of n-propanol (n-PrOH) and i-propanol (iPrOH) Taking into account the capacity of cyclodextrins (CD-s) to entrap a large number of organic and inorganic molecules, due to their hydrophobic cavity, β-CD has been introduced into PVA in order to obtain a good separation of isomer mixtures. Two methods for obtaining PVA/(β-cyclodextrins) (β-CD) blends have been reported: I.

membranes were prepared by casting the solution (4%) of PVA (PD=1650; saponification degree = 99.7 %) and β-CD in DMSO at 25 ºC and solvent evaporation at 80 ºC [83,84]; II. by casting the aqueous solution of PVA (Mn=125,000), β-CD and 0.1% glutaraldehyde and water evaporation at room temperature in a vacuum oven for 24 h [85]. PVA and β-CD evidenced a good compatibility and produce transparent blend films [84]. The blend membranes are permselective for different organic isomers. So, these could be used for the separation of n-propanol from a mixture of n-propanol (n-PrOH) and i-propanol (i-PrOH) [84] and the separation of p-xylene from a p-xylene and o-xylene mixture [35]. It was evidenced that, in both cases, the separation was better by applying the evapomeation technique than that of the pervaporation. It was observed that the n-PrOH concentration in the permeate through the CD/PVA membrane by pervaporation was approximately same as that in the feed solution, namely, the PrOH isomers could hardly be separated through these membranes by pervaporation. The nPrOH concentration in the permeate obtained by evapomeation was higher than that in the

124

Silvia Patachia, Artur J.M. Valente, Adina Papancea et al.

feed solution, evidencing a higher permeation of the CD/PVA membrane for n-PrOH compared to i-PrOH. The same situation was evidenced in the case of xylene isomers separation. The evapomeation is more efficient than that of pervaporation [83]. The n-PrOH concentration in the permeate and the normalized permeation rate increased with the increasing CD content in the CD/PVA membrane. The addition of CD in the PVA membrane determined the increasing of the swelling degree and preferential sorption of nPrOH and p-xylene, due to the fact that the affinity of CD for these isomers was stronger than that for i-PrOH and o-xylene respectively [84]. The influence of the CD content in the membrane and the n-PrOH respectively p-xylene content in the feed mixture on the separation factors and sorption and diffusion selectivities of the CD/PVA membranes for the n-PrOH/I-PrOH and p-xylene and o-xylene mixtures by evapomeation are presented in tables 12 and 13. Table 12. Separation factors and sorption and diffusion selectivities of the CD/PVA and PVA membrane for the n-PrOH/i-PrOH (50/50 w/w) mixture and p-xylene and o-xylene (10/90 w/w) mixture by evapomeation versus the CD content [18, 83, 84] CD content / / wt%

Separation of n-PrOH/i-PrOH (50/50 w/w) mixture αsorp. αdiff. αsep.

Separation of p-xylene and oxylene (10/90 w/w) mixture αsep. αsorp. αdiff.

0

2.01

1.89

1.06

1.72

0.53

3.27

20

-

-

-

1.19

0.94

1.27

30

-

-

-

2.93

1.08

2.74

40

2.61

2.07

1.26

3.93

0.78

5.04

Table 13. Separation factors and sorption and diffusion selectivities of the CD/PVA (CD content: 40 wt %) membrane for the n-PrOH/I-PrOH mixture and p-xylene and oxylene mixture by evapomeation versus the n-PrOH and respectively p-xylene, concentration in the feed [83,84] Content of feed / / wt% n-PrOH p-xylene 10 -

αsep.

αsorp.

αdiff.

15.2

3.68

4.14

50 -

10 30

2.61 3.93 3.26

2.07 0.78 1.86

1.26 5.04 1.75

-

50 70 90

1.86 1.99 0.63

1.06 1.48 1.03

1.75 1.34 0.61

It may be seen that a very high separation factor of organic liquid isomers through polymer membranes has been obtained for PrOH isomers [84].

Poly (Vinyl Alcohol)[PVA]-Based Polymer Membranes…

125

A similar situation is reported for the separation of xylene isomers [83]. These results show the CD/PVA membranes are good candidates for isomers separation from organic liquid mixtures by evapomeation. PVA/CD hydrogels swell in water. The swellability of PVA/CD hydrogels is marginally higher than that of the PVA gel, indicating that the crosslink density is higher in the PVA/CD system than in the PVA gel. The higher crosslink density may be an additional factor in retarding the migration of the drug in the presence of CD.

2.3. Separation by Pertraction Pertraction is a continuous membrane-based extraction process, which has been proposed for, e.g., removing metal and organic pollutants from waste water treatment [86] and for concentrating valuable components from complex broths in bioproduction [87] as a consequence of solvent extraction. In this technology, the membrane contactor combines two functions, i.e., separation and extraction. It generally consists of a hydrophobic liquid phase so that the extraction and stripping of the solutes occurs in a three-phase system with two liquid/liquid interfaces. To this purpose, different techniques, such as impregnation of a microfiltration membrane by a circulating hydrophobic phase, supported liquid membrane and hydrophobic membrane, have been applied [88]. A very effective way to improve the pertraction performances in permeability and selectivity is to incorporate extractants into the hydrophobic phase, which react with a given solute reversibly and selectively. S. Touil et al. [88] have reported the efficiency of membranes of cyclodextrin (CD)containing PVA membranes (with CD covently grafted to the polymer chain) for the geometrical xylene isomer discrimination using the pertraction (combination of separation and extraction) technique. They found that in the presence of CD-containing membranes permeability coefficients of xylene isomers are higher when compared to control PVA membrane. It is also reported that α-CD is more effective to selectively extract the xylene isomers than β-CD. Flux observed for pertraction of single isomers and of the o-/p- binary mixtures was in the same order as the binding constants to α-CD i.e.p-xylene > m-xylene > oxylene. The fabricated membranes exhibit a p-xylene selectivity for low p-xylene feed mole fraction (65