Proceedings of the International Conference on Colloid and Surface Science

Studies in Surface Science and Catalysis 132 PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON COLLOID AND SURFACE SCIENCE.TOKYO, JAPAN, NOVEMBER 5-8,2000

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Studies in Surfece Science and Catalysis Advisory Editors: B. Delmon and J.T. Yates Vol. 132

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON COLLOID AND SURFACE SCIENCE, Tokyo, Japan, November 5-8,2000 25th Anniversary of the Division of Colloid and Surface Chemistry, The Chemical Society of Japan Edited by Yasuhiro Iwasawa Department of Chemistry, Graduate School of ScienceJhe University of Tokyo, Hongo,BunkyO'lcu,Tol(yo 113-0033, Japan Noboru Oyama Department of Applied Chemistry, Faculty of Technology, Tokyo University of Agriculture and Technology, Nakacho, Koganei,Tokyo 184-8588, Japan Hironobu Kunieda Division ofArtificial Environment and Systems, Graduate School of Engineering, Yokohama National University, Tokiwadai, Hodogaya-ku,Yokohama 240-8501, Japan

2001 ELSEVIER Amsterdam —London - New York - Oxford —Paris — Shannon — Tokyo

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Preface The International Conference on Colloid and Surface Science was held from Sunday, November 5 to Wednesday, November 8, 2000 at Arcadia Ichigaya in Tokyo under the auspices of Division of Colloid and Surface Chemistry, the Chemical Society of Japan to commemorate the 25th anniversary of the foundation of the Division.

This special

volume of Studies in Surface Science and Catalysis contains articles submitted to the milestone Conference, financially supported by Grant-in-Aid for Publication of Scientific Research Result, the Ministry of Education, Science, Sports and Culture. The purpose of the Conference is to discuss the results of recent developments and the future prospect in science and technology of the field.

The field has been

growing andflourishing,while indicating many problems to be uncovered and solved. The Conference will be structured to encourage interactions and to stimulate the exchange of ideas to accomplish the above purpose. Key issues and materials related to the Conference were included as follows: (1) Molecular Assemblies in Solutions (micelles, surfactant solutions, emulsions and microemulsions, polymer solutions, gels, liquid crystals, etc.), (2) Fine Particles and Colloidal Dispersions (nano-micro fine particles, suspensions, polymer colloids, light scattering, electrokinetic phenomena, rheology, etc.), (3) Supramolecular Organized Films (insoluble monolayers, bilayers, Langmuir-Blodgett fibns, self-assembled monolayers, vesicles and liposomes, monoparticle films, biological aspects, etc.), (4) Nanostructural Solid Surfaces (adsorption in nanopores, catalysis, nanoparticle surfaces, functionalized surfaces, scanning probe microscopies, surface forces, nanotribology, microfabrication, colloids and interfaces in the environment, etc,), and (5) Industrial Applications and Products (energy and batteries: Li battery, Ni-hydrogen battery, fuel cell, gel, electrolyte, cosmetics and healthcare: skin-care, hair-care, drug delivery systems, foods: colloidal aspects of foods & foodstuff, processing, texture, nutrition, household: detergents, fabric-care, house-keeping goods, environmental applications, paint, etc.) The Conference comprised 2 plenary lectures, 42 invited lectures, 150 oral presentations and 266 poster presentations.

The camera-ready articles q^pearing in

this special issue were reviewed by expertsfroms^ropriate fields in accordance with standard guidelines of scientific journals in the field. The number of submitted papers

was much greater than we anticipated, reflecting the variety of scientific and technological activities in Colloid and Surface Science and the state of the Conference as an important event of the Division. We are grateful to the outstanding scientists in different fields of Colloid and Surface Science who accepted our invitation to overview vital research areas and to introduce the various topics of the sessions covered by the Conference.

We are also

grateful to Dr. Kostas I. Marinakis, Publisher, Dr. Matthias W.C. Wahls, Publishing Editor, and Drs. Huub Manten of Elsevier Science Publishers for the guidance and cooperation provided in getting this volume published in the book series of Studies in Surface Science and Catalysis. We believe that this Proceeding Book of the Conference may provide a valuable contribution towards a greater understanding of colloid and surface science, and also stimulate further developments and new ideas in future materials and processes.

Tokyo, November, 2000 The Editors

Table of Contents Preface

V

Plenary Session Structure of Liquid/liquid Interfaces Studied by Ellipsometry and Brewster Angle Microscopy G. H. Findenegg, J. Schulz and S. Uredat Assembly of Organic and Inorganic Molecular Layers by Adsorption from Solution T. Kunitake and I. Ichinose

1 15

Molecular Assemblies in Solutions Scattering Study of the Lyotropic Lamellar Phase in Aqueous Solutions of Nonionic Surfactants T. Kato, K. Minewaki, H. Yoshida, M Imai, and K. Ito

25

Microemulsions Composed of Metal Complex Surfactants, Bis(Octylethylenediamine (=0E)) Zn(II), Cd(II), and Pd(II) Chlorides, in Water / Chloroform and Water / Benzene Systems M. lida, H. Er, N. Hisamatsu, N. Asaoka and T. Imae 31 Kinetics of Lamellar to Gyroid Transition in a Nonionic Surfactant System M. Imai, A. Kawaguchi, A. Saeki, K. Nakaya, T. Kato and K. Ito

35

Efficiency Boosting by Amphiphilic Block Copolymers in Microemulsions: Dependence on Surfactant and Oil Chain Length R. Strey, M. Brandt, B. Jakobs and T. Sottmann

39

Thermotropic Phase Behavior of Binary Cationic Surfactant Mixtures in Water S. Kaneshina, H. Matsuki, R. Ichikawa and T. Kuwahara

45

Active Control of Surfactants N. L. Abbott

49

Droplet Microemulsion and Telechelic Polymer: Linear Rheology and Flow Instability at High Shear G. Porte, M. FilaH, E. Michel, J. Appell, S. Mora, E. Sunnyer and F. Molino

55

Synthesis and Micelle Formation of Fluorine-Containing Block Copolymers K. Matsumoto, T. Kitade, H. Mazaki, H. Matsuoka and H. Yamaoka

61

A Study of the Gelation of the Polysaccharide Curdlan H. Zhang, K. Nishinari, T. J. Foster, M. A. K. Wilhams and I. T. Norton

65

Formation of Highly Swollen L-Phases and Vesicle PhasesfromSingle Chain Surfactants by Chemical Reactions H. Hoffrnann, K. Horbaschek and J. Hao 69 Functions and Structures of Molecular Assemblies under High Magnetic Fields S. Ozeki

79

ESR Spectral Simulation Study of Oleic Acid/Oleate Solution by Using a Spin Probe H. Fukuda, A. Goto, H. Yoshioka and P. Walde

85

Controlled Association between Amphiphilic Polymers and Enzyme by Cyclodextrins in Heat Denatured Process: Artificial Molecular Chaperone K. Akiyoshi, M. Ikeda, Y. Sasaki and J. Sunamoto

89

Effect of Alcohols (Propanol, Propylene Glycol, and Glycerol) on Cloud Point and Micellar Structure in Long-Poly(oxyethylene)n Oleyl Ethers Systems K. Shigeta, U. Olsson and H. Kunieda 93 Critical Surface Charge Density for Counter-Ion Binding in Mixed Micelles of Ionic with Non-Ionic Surfactant M. Manabe, H. Kawamura, H. Katsu-ura and M. Shiomi

97

Dispersibility of Surfactant-Free OAV Emulsions and Their Stability Design: A Present Scope from Hydrocarbons to Some Oleate Esters K. Kamogawa, H. Akatsuka, M. Matsumoto, T. Sakai, T. Kobayashi, H. Sakai and M. Abe

101

Solidification of Liquid Hydrocarbons with the Aid of Carboxylate H. Sakaguchi

105

Methodology for Predicting Approximate Shape and Size Distribution of Micelles M. Kinoshita and Y. Sugai

109

Pre-Micelle and Micelle Formation of Local Anesthetic Dibucaine Hydrochloride H. Matsuki, T. Miyata, T. Yoshioka, H. Satake and S. Kaneshina

113

Ionic Partition to Zwitterionic Micelles K. Iso and T. Okada

117

Analysis of Local Structure of Ion Adsorbed on the Gas/Liquid Interface M. Harada, T. Okada and I. Watanabe Adsorption of Nonionic Surfactants, Triton X and Triton N, on Hydroxyapatite after Surface Modification with Sodium Dodecyl Sulfate in an Aqueous Phase S. Shimabayashi, M. Hoshino, T. Ohnishi and T. Hino

121 125

Miscibilty of Dodecylpyridinium Bromide and Dodecylquinolinium Bromide in Adsorbed Films and Micelle T. Fujii, K. Fujio and S. Ozeki 129 Interaction and Complex Formation of Pluronic Polymers with Ionic Surfactants S. Shimabayashi, A. Ichimori and T. Hino

133

Formation of Chiral Aggregates of Acylamino Acids in Organic Solvents H. Matsuzawa, H. Minami, T. Yano, T. Wakabayashi, M. Iwahashi, K. Sakamoto andD. Kaneko

137

Formation and Structure Control of Reverse Micelles by the Addition of Alkyl Amines and Their Applications for Extraction Processes of Proteins K. Shiomori, T. Honbu, Y. Kawano, R. Kuboi and I. Komasawa

141

Preparation and Surface-Active Properties of Cotelomer Type Surfactants of Alkyl Acrylate and Acrylic Acid T. Yoshimura, Y. Koide, H. Shosenji and K.Esumi

145

Iridescent and Coloured Colloidal Phases in Highly Dilute Systems Containing Decyl - and -D-glucopyranosides, Decanol or Octanol and Water B. Hoffmann and G. Platz

149

Complex Formation between Water-Soluble Calixarenes and Dodecylpyridinium Chloride K.Murakami 153 Influence of Oil Droplet Size on Flocculation/Coalescence in Surfactant-Free Emulsion T. Sakai, K.Kamogawa, F. Harusawa, N. Momozawa, H. Sakai and M. Abe

157

Morphology of Microemulsion Droplet Confining a Single Polymer Chain K. Nakaya, M. Imai, I. Miyata and M. Yonese

161

AOT Microemulsion Structure Depending on Both Apolar Solvent and Protein Concentration R. Kawai-Hirai, M. Hirai, H. Futatsugi, H. Iwase and T. Hayakawa

165

Phase Transition in Gibbs Monolayers of Mixed Surfactants M. M. Hossain, T. Okano and T. Kato

169

Mesoscopic Structures of J Aggregates of Organic Dyes at a Sohd/Liquid Interface and in Solution: Spectroscopic and Microscopic Studies H. Yao, S. Yamamoto, N. Kitamura and K. Kimura 173 Energy of Breaking of Aqueous GEMINI Surfactant Film T. Kidokoro and J. Igarashi

177

Molecular Aggregation States and Polymerizability of Potassium and Calcium 10-Undecenoates in Aqueous Systems Y. Shibasaki, H. Saitoh and A. Fujimori

181

Effects of Shear Flow on the Structure of the Lamellar Phase Formed in Nonionic Surfactant-Water System K. Minewaki, T.Kato and M. Imai

185

Solubility Behavior of Benzylhexadecyldimethylammonium Salts in Oils N.Ohtani

189

Deswelling Kinetics of Freeze-Dry-Treated Poly (A^-isopropylacrylamide) Gel in Sugar Solution N. Kato, S. Yamaguchi and F. Takahashi

193

NMR Study on the Effect of Added Salt on Alkylpyridinium Bromide Micelles S. Kobayashi, K. Fujio, Y. Uzu and S. Ozeki

197

Small-Angle Neutron Scattering Study of w/o AOT Microemulsion Entrapping Proteins M. Hirai, R. Kawai-Hirai, H. Iwase and T. Hayakawa

201

Neutron Spin Echo Investigations on Slow Dynamics in Complex Fluids Involving Amphiphiles T. Takeda, Y. Kawabata, H. Seto, S. Komura and M. Nagao

205

Neutron Spin Echo Studies on Effects of Temperature and Pressure in Dynamics of a Ternary Microemulsion Y. Kawabata, M. Nagao, H. Seto and T. Takeda

209

Dimerization of Penicillin V as Deduced by Frontal Derivative Chromatography S. Ishikawa, S. Neya and N. Funasaki

213

Two-Dimensional Clusters of Magnetic Fine Particles at the Surface of Magnetic Colloidal Suspension N. Tanaka, S. Doi and I. Takahashi

217

Colloid-chemical Properties of Chitosan S. Y. Bratskaya, M. V. Shamov, V. A. Avramenko and D. V. Chervonetskiy

221

Fine Particles and Colloidal Dispersions Science and Art of Fine Particles E. Matijevi

225

Hydrothermal Synthesis of Nano-Size ZrOa Powder, Its Characterization and Colloidal Processing O. Vasylkiv and Y. Sakka

233

Nanocrystal Self Assemblies: Fabrication and Collective Properties M. P. Pileni

237

Preparation, Characterization and Catalyses of Light-Transition-Metal/Noble-Metal Bimetallic Alloy Nanoclusters N. Toshima, P. Lu and Y. Wang

243

Novel Nanosize Borosilicate Colloid: Synthesis, Characterization, and Application J. M. Fu, A. Gerli, B. A. Keiser and A. Zelenev

247

Synthesis of Monodispersed Magnetic Particles by the Gel-Sol Method and Their Magnetic Properties H. Itoh and T. Sugimoto

251

Structural Change of Zinc Chloride Hydrate Melt Coexisting with Porous Solid Materials M. Mizuhata, Y, Sumihiro, A. Kajinami and S. Deki 255 Formation Conditions of Integrated Ordered Microstructure of Nano-size Silica Materials in Laurylamine/Tetraethoxysilane System M. Adachi, H. Taniguchi and M. Harada 259

Microscopic Morphology and SERS Activity of Ag Colloidal Particles M. Futamata, Y. Maruyama and M. Ishikawa

263

Effect of Polyvinylpyrrolidone on the Physical Properties of Titanium Dioxide Suspensions T. Sato and S. Kohnosu 267 Polymer Network Formation in the Pavement using SBR Latex Modified Asphalt Emulsions K. Takamura and W. Heckmann

271

Conformational Changes Induced by Competitive Adsorption in Mixed Interfacial Layers of Uncharged Polymers F. Csempesz and K. F.-Csaki 275 Electrostatic Potentials at Metal Oxide Aqueous Interface N. Kallay, D. Kova evi and I. Kobal

279

Microgravity Effects on the Properties of Colloidal Dispersions T. Okubo and A. Tsuchida

285

Colloidal Crystal Alloy Structure of Binary Dispersions of Polystyrene and Poly(Methylmethacrylate) Lattices by Ultra-Small-Angle X-ray Scattering T. Harada, H. Matsuoka and H. Yamaoka

289

The Role of Electrokinetic Properties on Adhesion of Nitrifying Bacteria to Solid Surfaces H. Hayashi, S. Tsuneda, A. Hirata and H. Sasaki 293 The Preparation of Porous Titania Films via Colloidal Crystallization between Electrodes Z.-Z. Gu, S. Hayami, Q.-B. Meng, A. Fujishima and O. Sato 297 Structure Formation of Poly(Furfuryl Alcohol)/Silica Hybrids S. Spange, H. Muller, D. Pleul, and F. Simon

301

Approach to a Unified Theory of Hydrophobic/Hydrophilic Surface Forces H.-J. Muller

307

Adsorption Behavior of Dispersing Agent to Pigment Surfaces N. Nakai, A. Hiwara and T. Fujitani

311

Measurement of Zeta Potentials in Concentrated Aqueous Suspensions of Ceramic Powders Using Electroacoustics R. Greenwood

315

Electrokinetic Phenomena in Concentrated Suspensions of Soft Particles H.Ohshima

319

Preparation of Nanosize Bimetallic Particles on Activated Carbon S. Hodoshima, T. Kubono, S. Asano, H. Arai and Y. Saito

323

Preparation of the PVA Film with Gold Fine Particles by a Counter Diffusion Method: Effect of Diffusion on the Distribution of Gold Fine Particles in the Film S. Sato, T. Shiono, H. Sato, M. Tsuji and M. Yonese

327

Optical Properties of ZnS: Mn Nanoparticles in Sol-Gel Glasses Y. Uchida and K. Matsui

331

Sonochemical Preparation of Noble Metal Nanoparticles in the Presence of Various Surfactants E. Takagi, Y. Mizukoshi, R. Oshima, Y. Nagata, H. Bandow and Y. Maeda

335

Liquid-Phase Synthesis of Y2O3: Eu Precursor Particles from Homogeneous Solution Y. Nishisu and M. Kobayashi

339

Processing of Zirconia and Alumina Fine Particles Through Electrophoretic Deposition Y. Sakka, B. D. Hatton and T. Uchikoshi

343

The Acceleration Behavior of Decomposition of Potassium Persulfate in the Dispersions of Polystyrene Particles Stabilized with Nonionic Emulsifier M. Okubo, T. Suzuki and S. Tasaki

347

Determination of the Size Distribution of Ultrafme Particles Based on a Measurement of Specific Surface Areas H. Yao, S. Yonemaru and K. Kimura

351

Dependence of Temperature-sensitivity of Poly (N-isopropylacrylamide-co-acrylic acid) Hydrogel Microspheres upon Their Sizes K. Makino, H. Agata and H. Ohshima

355

Deposition of Thiol-Passivated Gold Nanoparticles onto Glass Plates by Pulsed 532-nm Laser Irradiation: Effects of Thiol Y. Niidome, A. Hori, H. Takahashi and S. Yamada

359

Preparation of Silica-coated Magnetic Nanoparticles Y. Kobayashi and L. M. Liz-Marzan

363

Studies on the Preparation of Silica-Coated Carbon Particles by Sol-gel Method H. Shibuya, M. Shimada, N. Suzuki, H. Ito, K. limura, T. Kato and T. Kakihara

367

Synthesis and Catalysis of Polymer-Stabilized Ag and Ag/Pd Colloids Y. Shiraishi, K. Hirakawa, J. Yamaguchi and N. Toshima

371

Depletion Stabilization of Ceramic Suspensions with High Sohds Loading in the Presence of Zirconium Oxy-Salts O. Sakurada and M. Hashiba

375

Monte Carlo Study of Attractive Interaction between Charged Colloids T. Terao and T. Nakayama

379

Measurements of Elastic Constants of Colloidal Silica Crystals by Laser Diffraction T. Shinohara, T. Yoshiyama, I. S. Sogami, T. Konishi and N. Ise

383

Rheo-Optics of Colloidal Crystals T. Okubo, H. Kimura and T. Hatta

387

Relationship between the Electrorheological Effects and Electrical Properties in Barium Titanate Suspensions Y. Misono, N. Shigematsu, T. Yamaguchi and K. Negita

391

Solid-Liquid Separation and Size Classification of Ultra-fine Hematite Particles Using Bubbles K. Yamada, H. Hayashi, H. Sasaki and E. Matijevi

395

Rapid Separation of Oil Particles from Low Concentrated OAV Emulsion in the Presence of Surfactant using Surface Characteristics R. Sako, H. Ito, H. Hayashi and H. Sasaki 399 Fingering Pattern Dynamics in Magnetic Fluids Y. Enomoto

403

Coagulation of Negatively Charged Microspheres Dispersed in Cationic Surfactant Solution K. Fukada, K. Nakazato, T. Kato and M. Iwahashi 407 Nonlinear Electric Conduction in Zinc Oxide Suspension K. Negita, T. Yamaguchi, Y. Misono and N. Shigematsu

411

Heterocoagulation Behavior of PC Vesicles with Spherical Silica B. Yang, H. Matsumura, H. Kise and K. Furusawa

415

Electrokinetic Studies of Fullurene Dispersions in Aqueous Solutions of Surfactants H. Takahashi and M. Ozaki

419

Dynamic Mobility of Concentrated Suspensions in the Presence of Polyelectrolytes N. Tobori and T. Amari

423

Electrochemiluminescence Reactions of Metal Complexes Immobihzed on Surface of a Magnetic Microbead N. Oyama, K. Komori and O. Hatozaki

427

Fluorescence Spectra and Fluorescence Lifetime of Colloidal Solution of an Organic Dye, bis-MSB, and Third-order Optical Nonlinearities of Its Excitons K. Kasatani, H. Miyata, H. Okamoto and S. Takenaka 431 Supramolecular Organized Films Mechanistic Study of Model Monolayer Membranes and Their Interactions with Surfactants: Correlation to Effects on CHO Cell Cultures C. Yang, C. Ansong, L. Bockrath, J. J. Chalmers, Y.-S. Lee, M. O'Neil, J. F. Rathman and T.Sakamoto

435

Nanostructure and Dynamics of Polymers at the Interfaces by Neutron and X-ray Reflectometry E. Mouri, H. Matsuoka, K. Kago, R. Yoshitome, H. Yamaoka and S. Tasaki

439

Dynamic Cavity Array of Steroid Cyclophanes at Membrane Surface K. Ariga, Y. Terasaka, H. Tsuji, D. Sakai and J. Kikuchi

443

Mixed Langmuir Monolayer Properties of Sphingoglycolipids (Cerebrosides) and Lipids S. Nakamura, O. Shibata, K. Nakamura, M. Inagaki and R. Higuchi

447

Photoinduced Electron Transfer Processes in Polymer Langmuir-Blodgett Films T. Miyashita, S. Ugawa and A. Aoki

451

Monolayer Assemblies of Comb-Like Polymers Containing Fluorocarbons with Different Chain Length A. Fujimori, T. Araki, Y. Shibasaki and H. Nakahara 457 Self-organization of Amphiphilic Diacetylenes in Langmuir-Blodgett Films H. Tachibana, Y. Yamanaka, H. Sakai, M. Abe and M. Matsumoto

461

A Novel Understanding of Infrared Spectra of Langmuir-Blodgett Fihns by Factor Analysis T. Hasegawa, J. Nishijo and J. Umemura

465

Chemical Force Microscopies by Friction and Adhesion Using Chemically Modified Atomic Force Microscope (AFM) Tips M. Fujihira, Y. Tani, M. Furugori, Y. Okabe, U. Akiba, K. Yagi and S. Okamoto

469

In Situ Adsorption Investigation of Hexadecyltrimethylanmionium Chloride on Self-Assembled Monolayers by Surface Plasmon Resonance and Surface Enhanced Infrared Absorption Spectroscopy T. Imae, T. Takeshita and K. Yahagi

477

Molecular Assemblies Based on DNA-Mimetics:Effect of Monolayer Matrix on Photopolymerization of Diacetylene-Containing Nucleobase Monolayers K. Ijiro, J. Matsumoto and M. Shimomura

481

From Polymeric Films to Nanocapsules H. Mohwald, H. Lichtenfeld, S. Moya, A. Voigt, G. Sukhorukov, S. Leporatti, L. Dahne, A. Antipov, C. Y. Gao and E. Donath

485

The Effects of Substituents on the Aggregation of Bacteriochlorophylls CF and dp T. Ishii, H. Hirabayashi, F. Kamigakiuchi, M. Kimura, M. Kirihata, M. Kamikado, N. Tohge, Y. M. Jung, Y. Ozaki and K. Uehara

491

Dynamic Transformation of Liposomes Revealed by Dark-Field Microscopy F. Nomura, M. Honda, S. Takeda, K. Takiguchi and H. Hotani

495

Micelle-Vesicle Transition and Vesicle Size Determining Factor M. Ueno, H. Kashiwagi, N. Hirota and C. Sun

501

Active Control of Vesicle Formation with Photoelectrochemical Switching H. Sakai, A. Matsumura, T. Saji and M. Abe

505

Novel Cell Culture Substrates Based on Micro-Porous Films of Amphiphilic Polymers T. Nishikawa, J. Nishida, K. Nishikawa, R. Ookura, H. Ookubo, H. Kamachi, M. Matsushita, S. Todo and M. Shimomura

509

Nanoparticle Gold Preparation and Its Application in Biological Technology X. Y. Chen, L. Lin, Y. P. Deng, J. R. Li and L. Jiang

513

Strong Capillary Attraction between Spherical Inclusions in a Multilayered Lipid Membrane K. D. Danov, B. Pouligny, M. I. Angelova and P. A. Kralchevsky

519

Controlled Growth of Gold Nanoparticles in Organic Gels T. Yonezawa, M. Fukumaru and N. Kimizuka

525

A Model of Self-Assembling Nanoparticles due to Capillary Forces K. Yoshie, S. Maenosono and Y. Yamaguchi

529

Thin Films of Semiconductor Nanocrystals Self-Assembled by Wet Coating S. Maenosono, Y. Yamaguchi and K. Yoshie

533

Morphological Homogenization of Melamine Lipid Monolayer by Using Thermal Molecular Motion: Formation of Mesoscopic Pattem Based on Hydrogen Bonding Network T. Kasagi, M. Kuramori, K. Suehiro, Y. Oishi, K. Ariga and T. Kunitake

537

Formation and Structure of Organized Molecular Films of Fluorinated Amphiphiles with Vinyl Group A. Fujimori, T. Araki and H. Nakahara

541

Mixing Behavior of Binary Monolayer of Fatty Acid Based on -A Isotherm Measurement M. Kuramori, K. Suehiro and Y. Oishi

545

Fine Tuning of Chromophore Orientation Due to Hydrogen Bond Formation in Nucleobase-Terminated Azobenzene Monolayers M. Morisue, K. Ijiro and M. Shimomura

549

Monolayer and Bilayer Properties of Oligopeptide-Containing Lipids - Difference in Phase Transition Behavior S. Kawanami, T. Kosaka, T. Abe, K. Ariga and J. Kikuchi

553

Interactions of Sugars with Phosphatidylcholines H. Takahashi and I. Hatta

557

Study of J-Aggregate Formation of a Long-Chain Merocyanine in the Mixed LB Fihns and Their Optical Behavior M. Murata, T. Araki and H. Nakahara

561

Structure of H-Aggregate Formed in Merocyanine Dye LB Films Y. Hirano, T. M. Okada, Y. F. Miura, M. Sugi and T. Ishii

565

Impedance Analysis of Redox Polymer Langmuir-Blodgett Films A. Aoki and T. Miyashita

569

Molecular Orientation and Motion of Pyrene Molecules at the Interface of Polymer LB Films J. Matsui, M. Mitsuishi and T. Miyashita

573

Luminescence Properties of Europium Complexes in Polymer LB Films M. Mitsuishi, S. Kikuchi and T. Miyashita

577

Well-Defmed, Rigid Multiporphyrin Arrays: Interfacial Synthesis and Optical Properties in Monolayer Assemblies D.-J. Qian, C. Nakamura and J. Miyake

581

Surface Enhanced Infrared Absorption and UV-Vis Spectroscopic Study of a Monolayer Film of Protoporphyrin IX Zinc(II) on Gold Z. Zhang and T. Imae

585

Thermoreversible Vesicles with Semipolar Additives M. Gradzielski, H. Hoffmann, K. Horbaschek and F. Witte

589

Effect of L-Ascorbyl 2-Phosphates on Stability for Vesicles of Hydrogenated Soybean Lecithin S. Ban, K. Sasaki, S. Nakata and A. Kitahara

595

Novel Class of Organic-Inorganic Hybrid Vesicle "Cerasome" Derived from Various Amphiphiles with Alkoxysilyl Head K. Katagiri, K. Ariga and J. Kikuchi

599

Spin-Label Parameters of Detergent-Containing Liposomes and their Application to Micelle-Vesicle Transition H. Kashiwagi, S. Sagasaki, M. Tanaka, K. Aizawa, C. Sun and M. Ueno

603

Magneto fusion and Magnetodivision of Dipalmitoylphosphatidylcholine Liposomes H. Kurashima, H. Abe and S. Ozeki

607

Molecular Mechanism of Liposome Membrane Fusion Induced by Two Classes of Amphipathic Helical Peptides with Similar and Different Hydrophobic/Hydrophilic Balances T. Yoshimura, E. Sato, S. Lee and K. Kameyama

611

Stability of PA/PI Mixed Liposomes against Aggregation H. Minami, M. Iwahashi and T. Inoue

615

Preparation of Ultrathin Films Filled with Gold Nanoparticles through Layer-by-Layer Assembly with Polyions T. Yonezawa, H. Shimokawa, M.Sutoh, S. Onoue and T. Kunitake

619

Three Dimensional Assembly of Cationic Gold Nanoparticles and Anionic Organic Components: DNA and a Bilayer Membrane T. Yonezawa, S. Onoue and T. Kunitake

623

Preparation of Monolayers of Si02 and Ti02 Nano-Particles by Langmuir-Blodgett Technique M. Takahashi, K. Muramatsu, K. Tajima and K. Kobayashi

627

Size Controlled Mesoporous Silicate Thin Films using Block Copolymer as Template (I) T. Yamada, K. Asai, K. Ishigure, A. Endo, H. S. Zhou and I. Honma

631

Photocurrent of Purple Membrane Adsorbed onto a Thin Polymer Film: Effects of Monovalent and Divalent Ions A. Shibata, K. Yamada, H. Ikema, S. Ueno, E. Muneyuki and T. Higuti

635

Roles of Biomembranes - Effects of Surfactants Including Precursors of Endocrine Disrupters on the Interactions Between Acetylcholinesterase and Halothane I. Tsukamoto, H. Komatsu, T. Tsukamoto and N. Maekawa

639

The Effects of Alkyl Substituents and Formyl Group of Bacteriochlorophyll e on their Aggregation in Chlorosomes of Brown-Colored Photosynthetic Sulfur Bacteria H. Hirabayashi, T. Ishii and K. Uehara

643

Nanostructural Solid Surfaces Improved Molecular Models for Porous Carbons J. Pikunic, R. J.-M. Pellenq, K. T. Thomson, J.-N. Rouzaud, P. Levitz and K. E. Gubbins 647 Condensed Phase Property of Methanol in the Mesoporous Silica S. Kittaka, A. Serizawa, T. Iwashita, S. Takahara, T. Takenaka, Y. Kuroda and T. Mori

653

Structure and Relaxational Dynamics of Interfacial Water M.-C. Bellissent-Funel

657

Structural Analysis of Water Molecular Assembly in Hydrophobic Micropores Using in situ Small Angle X-Ray Scattering T. liyama, S. Ozeki and K. Kaneko

663

Synthesis, Characterisation and Chemistry of Transition Metals in Mesoporous Silica T. Campbell, J. M. Corker, A. J. Dent, S. A. El-Safty, J. Evans, S. G. Fiddy, M. A. Newton, C. P. Ship and S. Turin

667

Ethylene Hydrogenation on fee Ultra Thin Fe Films on a Rh(lOO) Surface - Effect of Co-Adsorbed CO and Growth Temperature C. Egawa, H. Iwai and S. Oki

673

Highly Isolated and Dispersed Transition Metal Ions and Oxides Studied by UV Resonance Raman Spectroscopy C. Li

677

Fluctuations in Nano-Scale Reaction Systems: Catalytic CO Oxidation on a Pt Field Emitter Tip R. Imbihl and Y. Suchorski

683

Why Copper Ion-Exchanged ZSM-5-type Zeolite Is So Active for CO Adsorption? - Comparison with Adsorption Properties of Silver Ion-Exchanged ZSM-5 Y. Kuroda, R. Kumashiro, H. Onishi, T. Mori, H. Kobayashi, Y. Yoshikawa and M. Nagao 689 Promotiong Effect of Zirconia Coated on Alumina on the Formation of Platinum Nanoparticles - Application on CO2 Reforming of Methane M. Schmal, M. M. V. M. Souza, D. A. G. Aranda and C. A. O. Perez

695

Structure Sensitivity in Reactive Carbon Dioxide Desorption on Palladium Surfaces M. G. Moula, S. Wako, M. U. Kislyuk, Y. Ohno and T. Matsushima

701

Conformational Order of Octadecanethiol(ODT) Monolayer at Gold/Solution Interface: Internal Reflection Sum Frequency Generation(SFG) Study S. Ye, S. Nihonyanagi, K. Fujishima and K. Uosaki

705

Doping Silver Nanoparticles in AOT Lyotropic Lamellar Phases X. Chen, S. Efrima, O. Regev, Z. M. Sui and K. Z. Yang

711

Modeling of the Kinetics of Metal Oxide Dissolution with Chelating Agents H. Tamura, M. Kitano, N. Ito, S. Takasaki and R. Furuichi

715

The Size-Induced Metal-Insulator Transition in Colloidal Gold P. P. Edwards, S. R. Johnson, M. O. Jones, A. Porch and R. L. Johnston

719

Design of Synthetic Glycolipids for Membrane Biotechnology M. Hato, J. B. Seguer and H. Minamikawa

725

Wetting of Ultrathin Layers of Polystyrene Studied by Atomic Force Microscopy S. Loi, M. Wind, M. Preuss, H.-J. Butt, H. W. Spiess and U. Jonas

729

Effect of Precursors on Structure of Rh Nanoparticles on Si02 support: in-situ EXAFS Observation during CO2 Hydrogenation K. K. Bando, H. Kusama, T. Saito, K. Sato, T. Tanaka, F. Dumeignil, M. Imamura, N. Matsubayashi and H. Shimada

737

Reduction of Photocurrents from Modified Electrodes with Cdi.xMnxS Nanoparticles in the Presence of Magnetic Fields H. Yonemura, M. Yoshida and S. Yamada

741

Ethylene Hydrogenation on fee Co Thin Fihns Grown on Ni(lOO) Surface C. Egawa, H. Iwai and S. Oki

745

Behavior of Pyridine on a Ti02(l 10) Surface Studied by Density Functional Theory T. Sasaki, K. Fukui and Y. Iwasawa

749

Observation of Indiviual Adsorbed Pyridine, Ammonia, and Water on TiO2(110) by Means of Scanning Tunneling Microscopy S. Suzuki, K. Fukui, H. Onishi, T. Sasaki and Y. Iwasawa

753

Three Dimensional Analysis of the Local Structure of Cu on Ti02(l 10) by in-situ Polarization-Dependent Total-Reflection Fluorescence XAFS Y. Tanizawa, W. J. Chun, T. Shido, K. Asakura and Y. Iwasawa

757

Insertion and Aggregation Behavior of PtCU between Graphite Layers M. Shirai, K. Igeta and M. Arai

761

Surface Properties of Silica-Titania and Silica-Zirconia Mixed Oxide Gels S. Ikoma, K. Nobuhara, M. Takami, T. Nishiyama, M. Nakamura and S. Kaneko

765

Characteristics of Supported Gold Catalysts Prepared by Spray Reaction Method L. Fan, N. Ichikuni, S. Shimazu and T. Uematsu

769

STM Observation of Oxygen Adsorption on Cu(l 11) T. Matsumoto, R. Bennett, P. Stone, T. Yamada, K. Domen and M. Bowker

773

Characterization of Si-O-C Ceramics Prepared by the Pyrolysis of Phenylsilicones Y. Tanaka, C. Mori, N. Suzuki, T. Kasai, K. limura and T. Kato

777

Structure and Growth Process of Niobium Carbide on Silica N. Ichikuni, F. Sato, S. Shimazu and T. Uematsu

781

In situ Energy-Dispersive XAFS Study of the Reduction Process of Cu-ZSM-5 Catalysts with 1 s Time-Resolution A. Yamaguchi, Y. Inada, T. Shido, K. Asakura, M. Nomura and Y. Iwasawa

785

Preparation and CO Hydrogenation Activities of Smectite-Type Catalysts Containing Cobalt Divalent Cations in Octahedral Sheets M. Shirai, K. Aoki, S.-L. Guo, K. Torii and M. Arai

789

Preparation of M0O3 by Spray Reaction Method and Photometathesis of C3H6 H. Murayama, N. Ichikuni, S. Shimazu and T. Uematsu

793

Molecular Mobility of Hydrogen-Bonded Acetonitrile on Surface Hydroxyls of MCM-41 with Kubo-Rothschild Analysis H. Tanaka, A. Matsumoto, K. K. linger and K. Kaneko 797 A Comprehensive Study of Surface State of MCM-41 having a Good Surface Crystallinity and Its Reactivity to Water Vapor T. Mori, Y. Kuroda, Y. Yoshikawa, M. Nagao and S. Kittaka 801 Vaporization and Oxidation of Poly- -Olefin on Metal Plates K. Hachiya

805

Molecular Geometry-Sensitive Filling in Micropores of Copper Complex-Assembled Microcrystals D. Li and K. Kaneko

809

Fluorescent Solubilizates in the Silica-Surfactant Composite Films K. Hayakawa, N. Fujiyama and I. Satake

813

Backbone Orientation of Adsorbed Polydimethylsiloxane I. Soga and S. Granick

817

Adsorption of Albumin on Organically-Modified Silicas (Ormosils) in Aqueous Solutions H. lyanagi, K. Yamane and S. Kaneko 821 Determination of the Acid-Base Properties of Surfaces by Contact Angle Titration with Buffered and Unbuffered Solutions H. Sakai

825

Sorption of Uranium(VI) on Na-Montmorillonite Colloids - Effect of Humic Acid and its Migration S. Nagasaki

829

Contribution of Preformed Monolayer to Micropore Filling T. Ohba, T. Suzuki and K. Kaneko

833

Magnetic-Field Control of Oxygen Adsorption H. Sato, Y. Matsubara and S. Ozeki

837

Viologen Monolayers: Dynamics on Electrode Surfaces T. Sagara, H. Tsuruta, Y. Fukuoka, S. Tanaka and N. Nakashima

841

Fluorescence Specific Micro Patterns in Two-Dimensional Ordered Arrays Composed of Polystyrene Fine Particles S. I. Matsushita, T. Miwa and A. Fujishima

845

Surface Force Measurement of Alumina Surfaces: Effect of Polyelectrolyte on the Dispersiveness of Aqueous Alumina Suspension R. Ishiguro, O. Sakurada, K. Kameyama, M. Hashiba, K. Hiramatsu and Y. Nurishi

849

Surface Properties and Photoactivity of Silica Prepared by Surface Modification M. Fuji, N. Maruzuka, T. Takei, T. Watanabe, M. Chikazawa, K. Tanabe and K. Mitsuhashi

853

Stability for Compressing Adsorbed Layers at Solid-Liquid Interface by the AFM Probe T. Kan-no, M. Fujii and T. Kato

857

Analysis of Bonding Nature being Operative in the M(Li, Na, K)Ion-Exchanged Zeolites CO Adsorption Systems R. Kumashiro, Y. Kuroda, H. Kobayashi and M. Nagao 861 Morphology of Octadecyltrimethylanmionium Halides Aggregates Adsorbed on Mica M. Fujii, T. Hasegawa and T. Kato

865

Photoinduced Long-Range Attraction between Spiropyran Monolayers Studied by Surface Forces Measurement Y. Nakai and K. Kurihara 869 Solid Monolayers of Simple Alkyl Molecules Adsorbedfromtheir Liquid to Graphite: the Influenece of Different Chemical Groups M. A. Castro, S. M. Clarke, A. Inaba, A. Perdigon, A. Prestidge and R. K. Thomas

873

Sorption Mechanism of lOs" onto Hydrotalcite T. Toraishi, S. Nagasaki and S. Tanaka

877

Thickness Dependence of Absorption of Molecular Thin Films Studied Using FECO Spectroscopy T. Haraszti, K. Kusakabe and K. Kurihara

881

Sorption of Neptunium on Surface of Magnetite K. Nakata, S. Nagasaki, S. Tanaka, Y. Sakamoto, T. Tanaka and H. Ogawa

885

Two Dimensional Auto-Organized Nanostructure Formation of Acid Polysaccharides on Bovine Serum Albumin Monolayer and Its Surface Tension S. Xu, T. Nonogaki, K. Tachi, S. Sato, I. Miyata, J. Yamanaka and M. Yonese

889

Trapping Behavior of Water on Metal Oxide and Active Desorption K. Chiba, T. Yoneoka and S. Tanaka

893

Effects of Adsorbed Water upon Friction at Layered K4Nb60i7-3H20 Surfaces Studied with FFM T. Sugai and H. Shindo

897

Sorption Behavior of Strontium onto C-S-H (Calcium Silicate Hydrated Phases) T. Iwaida, S. Nagasaki and S. Tanaka

901

Characterization and Direct Force Measurements of Fluorocarbon Monolayer Surfaces S. Ohnishi, V. V. Yaminsky and H. K. Christenson

905

Adsorption of Naphthalene Derivatives on Water-Soluble Polynuclear Aromatic Molecules Derived from Carbon Black K. Kamegawa, M. Kodama, K. Nishikubo and H. Yoshida

909

xxi

The Addition of Water and Alcohol to Alkenes by Alky-Immobilized Zeolite Catalysts in the Liquid Phase H. Ogawa, T. Hosoe, H. Xiuhua and T. Chihara

913

Magnetic Effects on Li' ExtractiodInsertion Reactions in Spinel-Trype Manganese Oxides Y. Kawachi, I. Mogi, H. Kanoh, K. Ooi, and S. Ozeki

917

Proton Conductivity and Water Adsorption Behavior of Complex Antimonic Acids K. Ozawa. Y. Sakka and M. Amano

92 1

Industrial Applications and Products High Performance Thin Lithium-Ion Battery Using an Aluminum-Plastic Laminated Film Bag T. Ohsaki, N. Takami, M. Kanda and M. Yamamoto

925

Surface Reactions of Carbon Negative Electrodes of Rechargeable Lithium Batteries Z. Ogumi, M. Inaba, T. Abe and S.-K. Jeong

929

Lithium Intercalation Mechanism of Iron Cyanocomplex N. Imanishi, T. Horiuchi, A. Hirano and Y. Takeda

935

New Lithium Insertion Alloy Electrode Materials for Rechargeable Lithium Batteries T. Sakai, Y. Xia, T. Fujieda and K. Tatsumi

939

Studies on the Interaction between Underpotentially Deposited Copper and 2,SDimercapto- 1,3,4-thiadiazole Adsorbed on Gold Electrode S. A. John, 0. Hatozaki and N. Oyama

943

Study of the Evolution of the LiElectrolyte Interface during Cycling of LiPolymer Batteries C. Brissot, M. Rosso, J.-N. Chazalviel and S. Lascaud

947

Analyses of the Preferential Oxidation of Carbon Monoxide in Hydrogen-Rich Gas over Noble Metal Catalysts Supported on Mordenite H. Igarashi, H. Uchida and M. Watanabe

953

Effects of Microstructure in Catalyst Layer on the Performance of PEFC J. Morita, E. Yasumoto, Y. Sugawara, M. Uchida and H. Gyoten

959

Ag-Etching Technique Based on Chemical Wet Process K.-S. Lee, J.-E. Park and S.-G. Park

963

Electrochemical Recognition of Ions with Self-Assembled Monolayers of Quinone Derivatized Calixarene Disulfide H. Kim, J. Kim, H. Lim, M.-J. Choi, S.-K. Chang and T. D. Chung

967

Milk Protein Adsorbed Layers and the Relationship to Emulsion Stability and Rheology E. Dickinson

973

Microscopic and Macroscopic Phase Transitions in Polyelectroyte-Micelle Systems P. L. Dubin

979

Self-Organization of Sucrose Fatty Acid Ester in Water K. Aramaki, H. Kunieda and M. Ishitobi

985

Development and Application of Microbial Transglutaminase Y. Kumazawa, T. Ohtsuka, K. Seguro and N. Nio

989

Fat Particle Structure and Stability of Food Dispersions D. T. Wasan, S. Uchil, A. D. Nikolov and T. Tagawa

995

The Investigation of Sodium N-Acyl-L-Glutamate and Cationic Cellulose Interaction N. Yamato, D. Kaneko and R. Y. Lochhead

1001

Properties of Aggregates of Amide Guanidine Type Cationic Surfactant with 1-Hexadecanol Adsorbed on Hair M. Arai, T. Suzuki, Y. Kaneko, M. Miyake and N. Nishikawa

1005

Preparation of 0/W/O Type Muhiple Emulsions and Its Application to Cosmetics T. Yanaki

1009

Visualization and Analysis of lontophoretic Transport in Hairless Mouse Skin B. D. Bath, J. B. Phipps, E. R. Scott, O. D. Uitto and H. S. White

1015

Development of New High Oil Contained Powder {Powder Gel) and Application to Powder Make-up H. Hotta, Y. Yago, R. Tsuchiya, M. Sasaki, H. Sugasawa, K. Minami, T. Minami and T. Suzuki

1021

Multiphase Emulsions by Liquid Crystal Emulsification and Their Application T. Suzuki, K. Yoda, H. Iwai, K. Fukuda and H. Hotta

1025

Rheology Studies to Investigate Sensorial Aspects of Emulsions K.-P. Wittem, R. Brummer and S. Godersky

1031

Effect of Chemical Structure on Aggregate Properties and Drag Reduction Behaviors of Quaternary Ammonium Salt Cationic Surfactant Solutions T. Horiuchi, T. Majima, T. Tamura, H. Sugawara and M. Yamauchi

1037

Interpretation of Foam Performance of Aerosol Type Glass Cleaner in Terms of Dynamic Surface and Interfacial Tensions M. Tanomura, Y. Takeuchi and Y. Kaneko

1041

NMR Specification of Lipid Bilayer Interfaces as Drug Delivery Sites E. Okamura, R. Kakitsubo and M. Nakahara

1045

Liquid/Liquid Extraction a New Alternative for Waste Water Remediation M. J. Schwuger, G. Subklew and N. Woller

1049

Characterization of Surfactants Used for Monodispersed Oil-in-Water Microspheres Production by MicroChannel Emulsification J. Tong, M. Nakajima, H. Nabetani and Y. Kikuchi

1055

Continuous Formation of Monodispersed Oil-in-Water Microspheres Using Vertically Mounted MicroChannel System I. Kobayashi, M. Nakajima and Y. Kikuchi

1061

X-ray Diffraction Study on Mouse Stratum Comeum N. Ohta, I. Hatta, S. Ban, H. Tanaka and S. Nakata

1067

Application of Self-Organizing Silicone Pol>iners for Long-Wearing Lipsticks M. Shibata, M. Shimizu, K. Nojima, K. Yoshino, H. Hosokawa and T. Suzuki

1071

Adsorption of Diols on Silica Gel Surface and Their Reactivities for Selective Monoacylation with Acetyl Chloride H. Ogawa, Y. Ide and T. Chihara

1075

Supported Liquid Film Catalyst and Biphasic Catalysis Using Water Soluble Metal Complexes in a Medium of Supercritical Carbon Dioxide B. M. Bhanage, Y. Ikushima, M. Shirai and M. Arai

1079

Effect of Oligosaccharide Alcohol Addition Concerning Translucent AI2O3 Produced by Slip Casting Using Gypsum Mold Y. Hotta, T. Banno, S. Sano, A. Tsuzuki and K. Oda

1083

Coal-Oil-Water Mixture Prepared by Disintegration of De-Ashed Coal Agglomerates H. Takase

1087

Author Index

1091

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Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) @ 2001 Elsevier Science B.V. All rights reserved.

Structure of Liquid/liquid Interfaces Studied by Ellipsometry and Brewster Angle Microscopy Gerfiard H. Findenegg, Jens Schulz and Steflfen Uredat Iwan-N.-Stranski Institut ftir Physikalische und Theoretische Chemie, Technische Universitat Berlin, StraBe des 17. Juni 112, D 10623 Berlin, Germany [email protected] Fax: +49 30 314 26602 The potential of ellipsometric measurements and the ellipsometric imaging technique for the study of structural properties of liquid/liquid interfaces is demonstrated. The ellipticity p of near critical interfaces in binary systems near an upper or lower critical solution point has been analyzed in terms of the Fisk-Widom profile n{z) of diffuse interfaces as well as theories of rough interfaces based on the coupling of thermal capillary waves. Phase transitions in Gibbs monolayers of simple amphiphiles (fatty alcohols and related substances) adsorbed at oil/water interfaces have been investigated by Brewster angle microscopy. The observation of domain patterns of the two coexisting phases provides direct evidence and unexpected aspects of the monolayer phase transition at this liquid/liquid interface. 1

INTRODUCTION

The interface between two liquids represents an inhomogeneous region in which local properties such as the number density or composition change in a smooth way fix)m the bulk value in phase a to that in phase (3. This feature becomes quite obvious in two-phase systems with high mutual solubility of the majority components. Such a situation arises when the constituent phases a and (3 are close to their consolute critical point. Near-critical interfaces have attained great interest since the days of van der Waals [1], and much progress towards a universal theory of simple fluid interfaces has been made in recent years [2, 3]. Apart from the structure normal to the interface, the interface may exhibit a lateral inhomogeneities on the length scale of micrometers or more. This case is met with adsorbed monolayers of amphiphiles at interfaces between chemically dissimilar liquids, such as oil and water. Within these monolayers the adsorbed molecules may be arranged in different ways, reminiscent of liquid, gaseous and liquid crystaline states of bulk phases. Like bulk-phases these interface phases undergo temperature dependent phase transitions. In two-phase coexistence regions the different monolayer phases cover patches of the interface with lateral extensions on a micrometer scale. Fluid interfaces are easily perturbed by mechanical devices as required in classical methods to study interfacial tensions and related properties of the interface. Noninvasive methods need to be used in the study the equilibrium structure of interfaces. In principle, reflectometiy of X-rays or neutons can yield detailed information about the interfacial composition profile on a molecular length scale [4, 5]. However, only recently

it has been possible to ^ply these methods to liquid/liquid interfaces [6]. Reflection ellipsometry of light represents a less demanding technique and is very useful for studying structural properties of interfaces in optically transparent liquid systems [7]. EUipsometry measures the state of polarization of light reflected at the interface (expressed by the coefficient of ellipticity), which is related to the profile of the refractive index in the direction perpendicular to the interface. Like X-ray and neutron reflecticity, ellipsometry is sensitive to the properties of the interfacial profile on a molecular length scale. In this article we will illustrate, how ellipsometric measurements can be used to elucidate structural features of different types of liquid/liquid interfaces: On the one hand, the thickness and composition profile of interfaces between coexistent nearcritical phases (critical interfaces) can be studied as a function of the distance from the critical solution temperature. Such systems are believed to constitute examples of weakly inhomogeneous interfaces. On the other hand, Brewster angle microscopy (BAM), a space-resolved imaging ellipsometric technique, was adapted to visualize lateral domain structures in monolayers of amphiphiles adsorbed at an oilAvater interface. Although BAM had been used successfully to study monolayer films of amphiphilic molecules at the free surface of water during the last decade [8], its application to the study of liquid/liquid interfaces is a relatively new technique developed in our laboratory. It was used to study monolayer phase transitions in Gibbs films of simple amphiphiles at the hexane/water interface. Some results of that study will also be discussed in this article. 2 STRUCTURE OF INTERFACES AND INTERACTION WITH LIGHT As explained in the Introduction, fluid interfaces do not represent sharp discontinuities at which the properties change abruptly in a step-like manner. Instead, real interfaces are best understood as inhomogeneous regions with non-vanishing gradients of the local number density and composition. These changes imply a characteristic profile of the refractive index and dielectric permittivity e in the direction normal to the interface, which in turn causes specific polarization properties of light reflected at the interface. In ellipsometric measurements a wave of polarized hght is reflected off the interface and the state of polarization of the reflected wave is analyzed. Generally, elliptically polarized light can be treated as the sum of two components, polarized in the plane of incidence (p-polarized) and perpendicular to this plane (s-polarized). Upon reflection, the amplitude and phase of the two components is altered. These changes in ampUtude and phase are represented by the complex reflection amplitudes, Vp = ppe*^^ and ^5 = PsC**' for p - and s-polarization, respectively, where p is the absolute amplitude and 5 is the phase of the wave. Ellipsometry measures the ratio of these two coefficients. It has its highest sensitivity at the Brewster angle OB^ where Ke(rp/rs) = 0, since at this angle of incidence tiiere is no background Fresnel contribution from the bulk phases. For sharp profiles (as compared with the wave length of light. A) the following relation was derived by Drude [9]:

= Im TT y/Cg -h 6f3 ^ ( g a - e{z)) (ejz)

X Ca - 60

J

- Ep) ^^

^^^

e(z)

— oo

where e = n^ represents the optical dielectric permittivity (square of the refractive index n) at the given wave length; Sa and cp denote the values in the two bulk phases (using the convention that the light wave is incident through phase /?), and £{z) is the dielectric permittivity along the normal coordinate z. The Dnide equation can be used in two different ways to attain information about the structure of interfaces: • Equation (1) allows to calculate p for parametric profile functions e(z) resulting from theoretical models of the interface structure, and to compare these theoretical predictions with experimental ellipticities. • In a more qualitative approach. Equation (1) can be used to translate trends of experimental p data (say, variations of p with temperature or composition) into changes of the interface profile 6(z), based on plausible qualitative models of the interfacial profile. Examples of the analysis of ellipsometric data for liquid/liquid interfaces in terms of the Drude equation are presented in the following section. 3 CRITICAL INTERFACES IN BINARY SYSTEMS Measurements of the absolute ellipticity were carried out in liquid/liquid systems close to the consolute critical point. Here the effective thickness of the inhomogeneous region between the bulk phases is proportional to the correlation length ^ of the critical fluctuations within the bulk phases. In this article we summarize some results for the interface between the constituent phases of phase-separated two-component systems close to the consolute critical point, at which the two phases become identical. For such interfaces, which are known as critical interfaces, one expects a marked increase of the thickness of the inhomogeneous region and/or an increasing roughness of the interface as the critical point is approached, and this increase of the effective interface thickness should cause a pronounced increase of p. Below it will be shown that this conjectured behavior is indeed observed. Critical interfaces in binary systems may exhibit either an upper critical solution temperature (UCST) or a lower critical solution temperature (LCST). Here we summarize briefly results for a nonaqueous system, hexane + perfluorohexane (CeH^ + CeF^), which exhibits an UCST, and an aqueous system of a short-chain amphiphilic compound, iso-butoxyethanol (i-C4Ei+water), wiiich exhibits a LCST, As the critical point

0.05 0.04 0.03

200

^\ _

160 El20

c 0.02

-/

0.01

f

^ ^

o

1

40 j_

)

h

9

t

0.01

0.02

0.03

^0

0.(

°

(T-TJ/Tc

0.01

0.02

0.(

(T-Tc)/Tc

Figure 2. 2-C4Ei + Water: Interfacial tension cr as a function of the temperature variable t = (T - Tc)/Tc and a fit of the data by cr = (TQI^ with ^=1.24.

Figure 1. i-C4Ei + Water: Refractive index increment An = np - Ua as a function of the temperature variable t = (T - Tc)/Tc and a fit of the data by An = Btf^ with ^=0.325.

is approached from the two-phase region, the mutual solubility of the two components increases and thus the compositions of the coexistent phases a and (3 become more and more alike, until at the critical point the two phases have become identical and the interfacial tension has disappeared. This behavior is exemplified in Figure 1 and Figure 2, where the temperature dependence of the refractive index increment An = rip — ria and of the interfacial tension a between the near-critical phases a and P of the system i-C4Ei+water is plotted as a function of the reduced temperature increment t = {T - Tc)/Tc, where Tc is the critical temperature. In the near-critical region for T -> T^ (t -> 0) the variation of An and a can be expressed by imiversal power laws, viz.. An

=

Tip —

UQ

= B t^

(2) (3)

where B and CTQ are material constants, while the critical exponents ^ and /i are expected to be universal constants for which modem theories of critical phenomena predict the values 0.325 and 1.26, respectively. In all cases studied by us these power laws are obeyed within experimental accuracy. Best-fit values for the parameters of the present systems are given in Table 1. Results for the ellipticity p of the critical interface a/0 of the two systems are presented in Figure 3. In both systems the magnitude of p increases progressively as the critical point is approached (t -^ 0). This behavior can be attributed to the growing thickness of the inhomogeneous interfacial region. Van der Waals theories [1, 2] relate the thickness of fluid interfaces to the correlation length ^ of critical composition fluctuations in the bulk phases. Following Fisk and Widom [10] the intrinsic composition

profile of the interface, expressed by the profile of the refractive index n, can be represented by a scaling function P{x) in the reduced length coordinate x = z/2^:

n{x) = where P(.)

=

-{ua-\-np)-\--{ria

- Ufs) P{x)

f^-M-) ^3 - tanh^(a:)

(4)

Inserting this profile function into the Drude equation (1) yields an expression for the ellipticity pi of the diffuse interface in terms of the correlation length ^ and refractive index increment Ua - np of the coexistent bulk phases,

where we have used the relation e = n^. Note that pi is proportional to the product of the refractive index increment An and the correlation length f of composition fluctuations in the bulk phases. These two quantities exhibit an antagonistic behavior in the critical region: while An tends to zero, the correlation length f increases and tends to infinity for t -^ 0 as The above power laws for An and f imply that the ellipticity resulting from the intrinsic profile of the interface will increase in magnitude and diverge as a power law PiCx{n^-n0)^

= B^ot-^''-^^

with 1/-/3 = 0.305. To test the above relation for p„ the correlation length ^ of the present systems was determined by turbidity measurements in the critical region. Best-fit values of the correlation length amplitude ^o are given in Table 1. Results for pi derived from the Fisk-Widom expression on the basis of our independent determinations of B and fo are shown as curve a in Figure 3. In these and other systems studied by us the Fisk-Widom theory yields a reasonable representation of the measured ellipticity data. Table 1. Parameters B^ CTQ and ^o in the power laws of the refractive index increment An, interfacial tension a, and correlation length ^, of binary systems near their critical solution temperature. The corresponding values of the critical exponents are /?=0.32; /i=1.26 and t/=0.63. _«.«««_ System B ao/mJm'^ ^o/^m z-C4Ei+Water CeHn+CeFn

0.116±0.005 0.218 ± 0.005

13.9±1.0 30.3 ± 1.0

0.35±0.02 0.20 ± 0.02

•

c

b

d

•

Te

5:^ Of

L

L.

0.01

0.02

0.03

-0.03

(T-Tc)/Te

-0.02

-0.01

(T-Tc)/Tc

Figure 3. Temperature dependence of the ellipticity p for two systems with critical interfaces near the critical temperature Tc. (left) 2-C4Ei+Water near the LCST; (right) CeH^+CeFH near the UCST. The curves represent calculations of p based on the Fisk-Widom theory of the intrinsic profile (eqn. 4; curve a), a combination of the Fisk-Widom theory and the capillary wave contribution (eqn. 6; curve d), and more sophisticated theories of critical interfaces). although close to the critical point pi determined in this way somewhat underestimates the experimental ellipticities. A different picture of fluid interfaces arises from the theory of thermally driven capillary wave fluctuations [11]. Unlike van der Waals theories, which treat interfaces as diffuse but flat, capillary wave theories consider the interface as sharp but rough. On the basis of the mode-coupling theory by Meunier [11] the ellipticity arising from the superposition of thermal capillaiy waves is 4.38 na-\-n0

(6)

Commonly the capillary wave expression p^w is of similar magnitude as p, (Equation 5) and, except for the weakly temperature-dependent prefactors, the two expressions exhibit the same temperature dependence. The effect of the capillary wave contribution to the ellipticity is shown in Figure 3 where the sum of the two contributions, pi + ^cw is shown as curve d. For most systems studied by us [12] it is found that pi +/Ocw somewhat overestimates the experimental ellipticities while pi, the ellipticity resulting from the intrinsic profile alone, falls somewhat below the experimental values. More sophisticated theories yield good agreement with the experimental ellipticities (curves 6 and c in Figure 3) without changing the underlying physical picture outlined above [12]. 4 PHASE TRANSITIONS IN GIBBS MONOLAYERS 4.1

Visualization of lateral structures

Soluble amphiphiles are preferentially adsorbed at oil/water interfaces. The decrease of the surface excess free energy due to this process can directly be monitored by measurement of the interfacial tension a. As the amphiphilic component is soluble

in one (or both) of the bulk phases, the adsorbed layer is always in thermodynamic equilibrium with the solution. The surface excess concentration F^^'^^ of the adsorbed amphiphile can be derived from concentration-dependent measurements of the interfacial tension using the Gibbs equation which, for constant temperature, yields r(i,2) "

L _ ^ RTdlnc

'

m ^ ^

where c denotes the equilibrium concentration of the amphiphile in one of the bulk phases. Adsorbed monolayers of amphiphiles are called Gibbs films. Gibbs films exhibit monolayer phase transitions in which the surface (excess) concentration shows discontinuous changes as a fimction of bulk concentration or temperature. Such phase transitions are causing a discontinuity of the slope of the interfacial tension as a fimction of temperature at the transition temperature Twise change of /^ at the transition temperature, perhaps with some hysteresis between descending and ascending temperature scans. However, such a step-wise change is not observed. Instead, the experiments yield a gradual increase of /^ with decreasing temperature, as shown in Figure 5. This increase commences at temperatures well below the nominal transition temperature as determined ex situ by interfacial tension measurements (Tt - T ^ 4 K). \^1thin experimental resolution, no hysteresis of Ir is observed. The capillary wave spectra taken in parallel with these measurements (cf Figure 5) show a change in the temperature behavior at 24 ""C, in good agreement with the transition temperature determined ex situ by the pendant drop measurements (cf Figure 4). BAM micrographs taken during the temperature scan reveal the appearance of circular domains of the condensed monolayer phase within a matrix of the gas-analogue phase (cf. Figure 6a). Domain formation starts approximately 4 K below the transition

10 908070605040-

•

1

1

*

\\

302010-

a /•> a -^5000 J

Q/i^ •

1

x^

kr

r ^

Xy'

* « « « « # «««iyarti 15

20

25

J 4000

30

T / 'C

Figure 5. Reflected intensity /^ (•,•) and peak frequency I/Q of capillary wave spectra (•), Gibbs film of FC12OH at the hexane/water interface vs. temperature T: full symbols, stepwise decrease of T; open symbols, stepwise increase of T.

Figure 6. BAM-images of a Gibbs film of FC12OH at different temperatures (see Fig. 5). a: 20^C, b: 12^C, c: 15°C. (a,b) stepwise decrease of T; (c) stepwise increase of T. temperature as determined by interfacial tension measurement and causes the observed increase of reflected intensity shown in Figure 5. On further decreasing temperature the area between these domains becomes smaller and finally the entire area of the interface is covered by a neat condensed film (Figure 6b). As the temperature is now increased, the domain pattem again occurs (Figure 6c), indicating that this domain morphology represents an equilibrium state of the system. 43.2

CisOH

Gibbs films of CigOH at the hexane/water interface exhibit a behavior similar to that of FC12OH layers. However, due to the favourable optical contrast, a higher resolution of the BAM micrographs can be obtained in this case as compared with

II

p#-^le Figure 7. BAM images of a Gibbs film of CigOH below the phase transition temperature. Contrast inversion resulting from a rotation of the analyzer (white bar represents a length of lOO^um) the former system. Here again, domains of the condensed phase can be observed at temperatures well below Tt. Unlike with FC12OH, circular domains of the condensed phase are found to coexist with extended (continuous) condensed regions (Figure 7). As shown in Figure 7, the contrast between the domains of condensed and dilute phase can be inverted by rotating the analyzer of the instrument. However, these changes of the analyzer setting do not lead to any sub-pattems within regions appearing in homogeneous brightness in Figure 7. This fact indicates that the observed domains are uniform in thickness and density, supporting the conjecture that they indeed represent monolayer domains of the alcohol film. (Otherwise, if the film would exhibit a non-imiform thickness profile, the local angle of incidence within a domain would be non-uniform and thus no sharp contrast inversion would occur on rotating the analyzer.) 43.3

Cholesterol and geraniol

Gibbs fihns of cholesterol and geraniol were found to show a similar behavior at the hexane/water interface. Results obtained for these two substances will be summarized here only briefly. As seen from Figure 4 the changes in the temperature dependence of the interfacial tension are much less pronounced for these substances than for FC12OH and CigOH. The BAM micrographs do not give any evidence of a true phase transition in the Gibbs fihns of these substances. Although a stepwise decrease of temperature leads to the formation of domain patterns below Tt (Figure 8), these domains are not stable and disappear a few minutes after the temperature step. It was found that the transient domains are more pronounced for greater temperature steps, but in any case they are unstable and disappear with time. No transient domains were observed for ascending temperature steps.

:>! Figure 8. Brewster angle micrographs of cholesterol (x = 7.110"^, after a rapid decrease of temperature from 35 to 20X) and geraniol (x = 3.4-10-^, after a rapid decrease of temperature from 25 to 22.5°C) 4.4 Discussion The observation of domain patterns in the BAM micrographs of Gibbs monolayers of the two simple alcohols at the hexane/water interface provides direct evidence of a phase transition and two-phase coexistence within Gibbs monolayers. Nontheless our findings provoce several questions as to the nature of these transitions: • If the observed transition represents a true first-order phase transition, two-phase coexistence should occur only at a singular transition temperature. So why does two-phase coexistence extend over a rather wide temperature range? • Why do the domain patterns appear only at a temperature some Kelvins below the transition temperature Tt as obtained by interfacial tension measurements? • Why are the patterns observed in films of cholesterol and geraniol unstable? A two-phase coexistence region extending over a finite range of temperature can be explained by assuming the presence of insoluble amphiphilic impurities. Assume, for simplicity, that the alcohol (A) contains a single surface active impurity (B) which is insoluble in the condensed surface phase of A, while A and B form an ideal mixture in the dilute (gas-like or expanded) surface phase. In this case the mole fraction of the impurity in the dilute surface phase (x%) is given approximately by [14] AH (Tt - T) (10) RTtT where AH is the molar enthalpy of the surface phase transition of pure component A and Tt is the transition temperature in the absence of the impurity. According to this simple relation the mole fi^action of the impurity in the dilute phase must increase as T is decreased. Now, when temperature is lowered both components will be adsorbed fix)m the subphase but while the majority component (A) can be accommodated in the condensed phase, the impurity (B) remains in the dilute phase. Accordingly, as the temperature is lowered the fi-action of surface covered by the condensed phase will increase while in the remainmg part of the surface the mole fraction of the impurity will increase in accordance with equation (10). In(l-x^):

13

The above conjecture does not explain why interfacial tension measurements indicate a phase transition temperature greater than the temperature at which domains of the condensed phase can be detected by BAM. Furthermore, we do not understand why condensed phase patterns of cholesterol and geraniol are unstable. These open questions indicate that phase transitions in Gibbs monolayers are more complicated than thought up to now, and our findings show the need for further experimental and theoretical work in this field. On the other hand, the results outlined above also show that BAM is indeed a useful tool for the study of Gibbs films at liquid/liquid interfaces. Future studies will take advantage of this new technique. Acknowledgement. The authors wish to thank Dr. P. Marczuk and B. Paeplow for help with the interfacial tension measurements. Discussions with Prof. S. Dietrich (Wuppertal) and Prof. B. Law (Manhattan, Kansas, USA) are gratefully acknowledged. This work was supported by the Deutsche Forschimgsgemeinschaft (DFG) under grant FI 235/11 as part of the Priority Program SPP 728 'Transportmechanismen " er fluide Phasengrenzen' . References 1. J.D. van der Waals, Verhandel Konink Akad Weten. Amsterdam (Sect. 1), Vol. 1, No. 8 (1893); Engl, translation (J.S. Rowlinson) in J. Statist. Phys. 20 (1979) 197 2. J.S. Rowlinson, B. Widom, Molecular Theory of Capillarity, Clarendon Press, Oxford, 1982 3. H. Ted Davis, Statistical Mechanics of Phases, Interfaces and Thin Films, VCH Publishers, New York, 1996 4. A. Braslau, M. Deutsch, P.S. Pershan, A.H. Weiss, J. Als-Nielsen, J. Bohr, Phys. Rev. Lett. 54 (1985) 114; J. Als-Nielsen, Physica B 126 (1984) 145 5. P. Lang, in Modern Characterization Methods of Surfactant Systems, Surfactant Science Series, Vol. 83 (B.R Binks, ed.). Marcel Dekker, 1999, chap. 10; R.K. Thomas, ibid, chap. 11 6. D.M. Mitrinovic, Z. Zhang, S.M. Williams, Z. Huang, M.L. Schlossman, J. Phys. Chem. B 103 (1999) 1779; Z. Zhang, D.M. Mitrinovic, S.M. Williams, Z. Huang, M.L. Schlossman, J. Chem. Phys. 110 (1999) 7421 7. D. Beaglehole, in Fluid Interfacial Phenomena (C. A. Croxton, ed.), Chichester, 1986, chap. 11 8. S. Henon, J. Meunier, in Modern Characterization Methods of Surfactant Systems (ref 5), chap. 4 9. R Drude, Ann. Phys. Chem. (Leipzig) 43 (1891) 91

14

10. S. Fisk, B. Widom, J. Chem. Phys. 50 (1969) 3219 11. J. Meunier, in Light Scattering by Liquid Surfaces and Complementary Techniques, Surfactant Science Series, Vol. 41 (D. Langevin, ed.), Marcel Dekker, New York, 1992, p. 333 12. J. Schulz, A. Hirtz, G.H. Findenegg, Physica A 244 (1997) 334 13. D. Vollhardt, Adv. Colloid Interf, Scl 64 (1996)143; V. Melzer, D. Vollhardt, Phys. Rev. Lett. 76 (1996) 3770; D. Vollhardt, V. Melzer, J. Phys. Chem. B 101 (1997) 3370 14. S. Uredat, G.H. Findenegg, Langmuir 15 (1999) 1108 15. S. Uredat, G.H. Findenegg, Colloids and Surfaces A 142 (1998) 323 16. D. Langevin, in Light Scattering by Liquid Surfaces and Complementary Techniques, Surfactant Science Series, Vol. 41 (D. Langevin, ed.). Marcel Dekker, New York, 1992, chap. 2 17. N. Matubayasi, K. Motomura, M. Aratono, R. Matuura, Bull. Chem. Soc. Japan 51 (1978) 2800; T. Ikenaga, N. Matubayasi, M. Aratono, K. Motomura, R. Matuura, Bull. Chem. Soc. Japan 53 (1980) 653; H. lyota, M. Aratono, K. Motomura, R. Matuura, Bull. Chem. Soc. Japan 65 (1983) 2402 18. Y. Hayami, A. Uemura, N. Ikeda, M. Aratono, K. Motomura, J. Colloid Interf. Sci. 172 (1995) 142; T. Takiue, A. Yanata, N. Ikeda, Y. Hayami, K. Motomura, M. Aratono, J Phys. Chem. 100 (1996) 20122 19. M. Matsuguchi, M. Aratono, K. Motomura, Bull. Chem. Soc. Japan 63 (1990) 17

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) c 2001 Elsevier Science B.V. Ail rights reserved.

15

Assembly of organic and inorganic molecular layers by adsorption from solution T. Kunitake and L Ichinose The iDStitute of Riysical and Chemical Research (RIKEN), Frontier Research System 2-1, Hirosawa, Wako, Saitama 351-0198 JAPAN Fax: +81-48-464-9361 E-mail: [email protected] 1. Introduction Fabrication of ultrathin molecular films can be classified as either dry or wet. Diy processes involve depositions of precursors and monomers in vapor phase onto solid sur&ces. Activation of reactants by plasma is one of the most commonly used methods for chemical vapor deposition. It, however, often results in structures that do not allow detailed characterization. The Langmuir-Blodgett technique has been ahnost the sole wet method to prepare ordered, moleculariy-thin films in the past several decades. This situation changed recently, and newer techniques based on physi-sorption and chemi-sorption of small molecules and polymers became widely used. Simple adsorption processes can produce regular molecular layers, if proper preparative conditions are employed. 2. Polymerizatioii-Induced Adsorption ,S.

NH, H In-situ deposition of primarily insoluble conductive polymers has been studied by several groups. Gregory et al. pyrrole aniline 3-hexylthiophene obtained uniform thin films of polypyrrole (1) and polyaniline (2) on textile substrates (2) (3) during polymerization via adsorption of an intermediate from solution. Paley et al. succeeded in photodeposition of HoN-, ^ - o - • Q ^ N H , polydiacetylene films from the monomer N=C=0 solution and used it for the surface tolyiene-2,4-diisocyanate 4,4'-oxydianiline patterning. Combination of in-situ (5) (4) deposition and electrostatic altemate adsorption was recently explored by Rubner and his co-woricers. ' p-Doped conjugate polymers, such as polypyrrole, polyaniline and poly(3-hexylthiophene) (3), were directly adsorbedfix)mdiluted polymerization solutions, and the substrate was subsequently inunersed in poly(styrenesulfonate) solution. Polypyrrole is uniformly adsorbed on a negatively-chaiged precursor surface. A typical example of the polymerization-induced adsorption is given in Figure la. A gold-coated QCM resonator is inunersed into a fiiesh polymerization solution. After recording the fi:equency change, the electrode is immersed again into a newly prepared

6

6

16

polymerization solution, hisoluble polymer occasionally precipitates finom the reaction mixture, but they are readily removed by washing. Frequency shifts during repeated adsorption of polypynole (1) are shown in Figure lb. The oxidative polymerization was started by adding a small amount of copper ( E ) chloride into pyrrole in propanol. The frequency changes observed here point to regular growth of an ultrathin fihn of polypyrrole with thickness increase of 12 ± 5 nm. Apparently, more than ten molecular layen of polypyrrole are adsorbed during a single adsorption process. The XPS and UV-VIS-NIR spectra mdicate that this film contains a small amount of copper atoms used as oxidation catalyst. Figure 2 shows a scaiming electron micrograph of the cross section of a polypyrrole fihn of 90± 10 nm thickness deposited onto a gold-coated QCM resonator.

b) ^5000: X ^

4000Polypyrrole

1

Polymenzation solution

/C^K J

o c Measurement of frequency

1 ^/

E 3000 •

«

Drying

£ "^ Washing

v\ ^A

Polyiirea i

oi 0

1

2

4

i i

1 1

6

1

8

Cycles of polymerization

Figure 1. (a) Schematic illustration of polymerization-induced adsorption, (b) QCM frequency shifts with cycles of polymerization. Another case of the polymerization-induced adsorption is a polyurea thin film. Repeated inunersion in a 1:1 mixture of 4,4'-oxydianiline (4) and tolylene-2,4-diisocyanate (5) gives regular adsorption of 8 ± 2 nm in each cycle. Reflection IR spectroscopy of this fihn indicates formation of the urea linkage via polyaddition of amine and isocyanate groups along with 17 % of uiueacted isocyanate groups. The extent of the adsorption was fairiy constant among different polyureas, although film morphologies are widely varied.^ 3. Polymerization-Induced Epitaxy

Figure 2. Scanning electron micrographs of polypyrrole thin film.

When a flat, crystalline soUd is immersed in a polymerization solution, an ultrathin film of ordered polymer chains may be foimd on the sohd surface. Stmctural analyses indicate regular aUgrunent of almost all train chains with an epitaxial orientation. ' The polymerization process itself is indispensable for film growth, and we refer to this epitaxial adsorption as polymerization-induced epitaxy. Freshly

17 cleaved, highly oriented pyiolytic graphite is convenient as substrate. After polymerization, the substrate is taken out of thereactionmixture and is rinsed exhaustively with solvents of polymers. The first polymer layer on the surface is insoluble in common solvents, probably due to difficulty in solvating epitaxially adsorbed highly packed chains. Ring-opening polymerization by cationic and anionic catalysts, radical polymerization, polycondensation and polyaddition are found to yield oriented films on graphite. Thus any one-phase solution polymerization appears to induce film growth as long as the substrate surface remains chemically intact. The film morphology and the surface coverage depend heavily on polymerization conditions such as concentration, temperature, andreactiontime. Figure 3 is a probable aUgmnent of PTHF chain based on scanning tunneling microscopy (STM) images. Planar zigzag chains in all-trans conformation lie so that every ethylene unit is commensurate with the graphite hexagonal lattice. This film was polycrystalline, as other orientations as well as different chain packings were observed on the same sample surface. Polycrystalline structures were also observed for aliphatic and aromatic polyesters.

kb^b^'f :^-. 4.3 A'""(

ly^}/?'^^'^ \, }'-/'"(

'Xy^'^

.>--«'''""*
#

4.5

30

40

50 60 //'C

70

80

Fig. 1. Temperature dependence of the repeat distance d at different concentrations. The dashed lines indicate the micellar/lamellar coexistence region. The d values at the temperatures lower than 60°C at 32 and 40 wt% are obtained for the micellar phase.

Fig. 2. Double logarithmic plot of the repeat distance rfvs. volimie fraction of the hydrophobic layer ^c. Ordinate is arbitrarily shifted. The solid Unes are the least-square fits to the relation d oc ^c~^. The region between the two vertical bars indicate the micellar/lamellar coexistence region. The symbols located at the lower concentrations than these bars indicate the lvalues for the micellar phase.

28

indicating that the possibiUty of coexistence with other phases can be excluded. The above discussion is based on the assumption that Ac is constant. If (Sic depends on the concentration, 5 may deviate from unity even if Eq.(l) holds true. So we have analyzed line shape of SAXS to determine Ac directly. 3.2 Line shape analysis In the line shape analysis, we assume that layer displacement fluctuations are independent of the transverse position. Then the scattering intensity can be written in terms of the form factor of a membrane B^q) and the structure factor S{q) as [12] I(q) = (2 7z/d)I\q)S(q)/q^

(2)

In the calculation of I\q), the membrane is assumed to be composed of three layers; one hydrophobic layer and two hydrophihc layers. Then I(q) can be expressed as a function of Ac, the thickness of the hydrophilic layer, and a AA A A A A

^ 0.8

30

40

50

60

t/'C

Fig. 3. Temperature dependence of the exponent s obtained from the least-square fitting of the data in Figure 2. The solid line is an aid to the eye.

10 20

30 40 50 60 wt%

70

80

Fig. 4. Phase diagram of C16E7-D2O system, redrawn from figure 1 in Ref.[5]. La, lamellar phase; Vi, cubic phase; Hi, hexagonal phase; Nc, nematic phase; Li, isotropic micellar phase; and W + Li, coexisting liquid phases. Filled and open triangles indicate the presence and absence of the broad component, respectively. The dotted lines are constant contours of A, (see Eq.(3)). The dotted hnes in the Li phase indicate constant contours of the activation energy for self-diffusion processes.

29 parameter correlated with the layer displacement fluctuations. We have determined these parameters by the least-square fitting of g^/(g) because /(^) is inversely proportional to ^ . Figure 5 (left) shows examples of observed SAXS data and least-squares fits. It has been found that the Ac value thus obtained depends on concentration and temperature only slightly [9], suggesting that the deviation of-5 from unity is not due to the variation of Ac but due to the change in the structure itself. 3.3 Relations with phase behaviors and structures of micellar phase For the CieEe system, existence of water-filled defects has been proposed by Holmes's group [6-8]. In this case, ^ c can be expressed as (3)

^ c = (1 - fv,)(2St,c)/d

where £,v is the volume fraction of the defects. We have tried to calculate £N at each concentration and temperature by utilizing Ac values which satisfy the relation ^c^= 2dticld^ (d^: lower limit of the repeat distance) corresponding to the assumption that defects disappear at ^c^. Based on the results in Figure 1, we set d^ = 4.63 nm. Although the absolute value of i?v depends on d^, this does not affect the discussion below. Figxire 4 contains the lines where fw is constant. As

q /nm-

q I nm-^

Fig. 5. Examples of SAXS patterns, left: Least-squares fits of g*/at 75°C (40, 51, and 55 wt% fi-om the bottom), right: Logarithm of the SAXS intensity at 48 wt% (55, 60, 65, 70, 75°C firom the bottom).

30

can be seen from the SAXS patterns in Figure 5 (right), a broad component is superimposed on the first diffraction peak at 55 and 60°C. The filled and open triangles in Figure 4 indicate the presence and absence of the broad component, respectively. It can be seen from the figure that the broad component is observed in the region where i?v is relatively large. The observation of such a broad component has been already reported for the CieEe system [6-8] where it has been assigned to the reflection from the water-filled defects. This assignment is consistent with the strong correlation between £s and the appearance of the broad component in the present system. As described in the introduction, our previous studies [1-5] suggests that in the Li phase three-dimensional networlc is formed in the vicinity of the "La" and Vi phases. The dotted lines in the Li phase indicate constant contours of the activation energy for self-diffusion processes (40, 60, 80, 100, 120, 140, and 160 kJ mol-i firom the top) which can be regarded as the measure of the fraction of such a network. On the other hand, bilayer sheets with water-filled holes can be regarded as two-dimensional network. In the lower concentration range in the "La" phase, gradual transition into such a structure occurs by the reduction of temperature. Then the structures of the "La" and Li phases become similar as the temperature decreases. It should be noted that £N takes a maximum near the boundary with Li and Vi phases. As can be seen from Figure 2, there is only a small discontinuity in the repeat distance at the "La" to Li transition in the lower temperature range. On the contrary, the repeat distance is not continuously varied at the "La" to Li transition in the higher temperature range (see Figure 1). All these results are consistent with the variation in the structure of the "La" phase described above. REFERENCES 1. T. Kato, T. Terao, and T. Seimiya, Langmuir, 10 (1994) 4468. 2. T. Kato, N. Taguchi, T. Terao, and T. Seimiya, Langmuir, 11 (1995) 4661. 3. T. Kato, Prog. Colloid Polym. Sci., 100 (1996) 15. 4. T. Kato, N. Taguchi, and D. Nozu, Prog. Colloid Polym. Sci., 106 (1997) 57. 5. T. Kato and D. Nozu, J. Mol. Liquid, in press. 6. M.C. Holmes, M.S; Leaver, A.M. Smith, Langmuir, 11 (1995) 356. 7. S.S. Funari, M.C. Holmes, G.J.T. Tiddy, J. Phys. Chem., 96 (1992) 11029, 98 (1994) 3015. 8. C.E. Fairhurst, M.C. Holmes, M.S. Leaver, Langmuir, 12 (1996) 6336, 13 (1997) 4964. 9. K. Minewaki, T. Kato, H. Yoshida, M. Imai, K. Ito, submitted to Langmuir. 10. S.T. Hyde, Colloque de Physique, 51 (1990) C7-209. 11. S.T. Hyde, CoUoids and Surfaces A, 103 (1995), 227. 12. F. NaUet, R. Laversanne, D. Roux, J. Phys. II France, 3 (1993) 487. 13. M. Imai, A. Kawaguchi, A. Saeki, K. Nakaya, T. Kato, K. Ito, Y. Amemiya, Phys. Rev. E, in press.

Studies in Surface Science and Catalysis 132 Y. iwasawa, N. Oyama and H. Kunieda (Editors) ^c 2001 Elsevier Science B. V. All rights reserved.

31

Microemulsions composed of metal complex surfactants, bis(octylethyienediamine (= OE)) Zn(II), Cd(II), and Pd(II) chlorides, in water/ chloroform and water/benzene systems Masay asu lida,* Hua Er,^ Naoko Hisamatsu,* None Asaoka,^ and Toy oko Imae ^ ^Department of Chemistry, Nara Women's University, Nara 630-8506, Japan ^ Research Center for Materials Science, Nagoy a University, Nagoy a 464-8602, Japan Bis(A^-octylethylenediamine (= OE)) zinc(II), cadniiiun(II), and palladium(II) complexes (Zn(OE)2Cl2, Cd(OE)2Cl2, and Pd(OE)2Cl2) were prepared, and the characteristic structures of the aggregates were investigated in such mixed solvents as water/chlorofomi, water/benzene, and water/methanol using ^H NMR pulsed-gradient spin echo (PGSE) and TEM (transmission electron microscopy) methods. These complexes form reverse micelles or w/o microemulsions in water/chloroform or water/benzene depending on the hydrophilicity of the headgroup. 1. INTRODUCTION Double-chained surfactants of metal complexes have shown unique aggregation behavior in orgsnic solvents or water,^"^ since their HLB is intermediate and they sometimes display characteristic stereochemistry."* We have prepared such kinds of metal complex surfactants as Zn(OE)2Cl2, Cd(OE)2Cl2, and Pd(OE)2Cl2. They are readily to form singje crystals and not hygroscopic. They are thus desirable for the X-ray crystallographic analysis as doublechained surfactants. We have previously clarified the structures of the Zn(II) and Pd(II) complexes in crystals as follows.^'^ In the former complex, the geometry is octahedral, the aniono groups are tram, and the octyl chains are transoid; on the other hand, in the Pd(II) complex the geometry is square planar and the chloride ions are not coordinated. The molecular structure of rra/i5-dichloro-/ra«5oa/-bis(A^-octylethylenediamine)zinc(II) complex is given in Fig. 1. In the present paper, we report the solubilities and aggregation behavior of M(OE)2Cl2 (M= Zn, Cd, Pd) in water/methanol, water/chloroform and water/benzene systems in comparison of the metal-chloride interactions between the three metals. 2. EXPERIMENTAL The M(OE)2Cl2 (M= Zn, Cd, and Pd) complexes were prepared according to the previous

32

methods. ^'^ The purities were confirmed by elemental analysis and ^^C NMR spectra. The selective solubilities of the complexes in water/chloroform or water/benzene system were visually determined and the ternary phase diagrams were drawn. The aggreg3tion behavior was studied by the measurements of diffusion coefficients of the complexes and water on a JEOL FX 90 NMR spectrometer. The diffusion coefficients were reproducible within a precision of 5% or better. TEM was observed on a Hitachi H-800 electron microscope at an accelerating voltage of 100 kV. Freeze-fracture repUcas were prepared by using a Balzers cryofract (BAF-400). Details of the procedure were described elsewhere. "^» ^ 3. RESULTS AND DISCUSSION All the complexes are poorly soluble in water (around 1% for the palladium complex and below 0.1% for the zinc and cadmium complexes). The Zn(II) and Cd(II) complexes are significantly soluble in chloroform while the Pd(II) complex is poorly soluble. The solubilities in chloroform increased with the addition of water; for the palladium complex, the magnitude was especially large in spite of the low solubility in neat water. Partial ternary phase diagrams for the three complexes in water/chloroform mixed solvents are given in Fig 2. It is remarkable that the palladium complex has a large L2 region, which reflects its hi^er hydrophilicity (or polarity) of the headgroup caused by the ionic character of the palladiumchloride bond. In the Zn(II) and Cd(II) complexes, on the other hand, the chloride ion coordinates to the metal center in crystal. The strength of the metal-chloride bond in the complexes would be in the order, Cd(OE)2Cl2 > Zn(OE)2Cl2 » Pd(OE)2Cl2, whereas in the simple chloride salts the covalency of the metal-chloride ion bond is in the order, PdCl2 > CdCl2 > ZnCl2.

(a) H2O-X 40 Cd(OE)2 V60

. 80

^ CIF Pd(OE)2 \60

CIF H2O-

H2O 40

Fig 1. A molecular structure of Zn(OE)2Cl2. (In Figures, M(OE)2Cl2 is abbreviated as M(0E)2.)

^ 60

60

80

CIF 40

60

80

Fig 2. Partial mass (wt %) ternary phase diagram for the three complexes in water/chloroform (CIF) mixed solvents. L2 is water in oil phase.

33

Figure 3 shows the diffusion coefficients for water and the Zn(II) complex in the chloroform and methanol systems as functions of the complex concentrations. Appreciable decrease in the water diffusion coefficients compared to that for the neat water (2.32x10"^ m^s~^) means the motional restriction of water molecules by the Zn(II) complex We furthermore found that the addition of water slightly (20-30%) retards the diffusion of the Zn(II) complex in the concentration ranges of 0.5-1.0 mol kg"^ in the chloroform system. This result suggests the formation of aggregates incorporating water. The trend for the diffusion coefficients in the Cd(II) complex system was similar to that in the Zn(II) complex system, as seen for the solubility behavior. (Fig. 2) The difference in the diffusion coefficients between the Zn(II) complex and water is significantly smaller in the chloroform system (Fig 3) compared to the methanol (Fig 3) and benzene (Fig 4) systems. The diffusion coefficients and phase diagrams suggest that the reverse micelles are formed for the Zn(II) and Cd(II) complexes in water/chloroform medium, while the microemulsions are formed for the Zn(II) and Cd(II) complexes in water/benzene and for the Pd(II) complex in water/chloroform. (Fig. 5) It is characteristic that the diffusion coefficients of water molecules and metal complexes increase with an increase in water content in the Pd(II) microemulsion system (Fig 5) while they decrease in the Zn(II) (Fig 4) and Cd(II) systems. In the Pd(II) complex system, the degree of the dissociation of the chloride ion would be larger compared to the other two metal systems since the Pd-Cl bond is more ionic; therefore, water molecules may more easily move from one water pool to the other ones together with the chloride ions. 10*

^ :

HDD in MeOD Zn(0E)2 in MeOD

• •

HDO in GIF Zn(0E)2 in GIF iWo'

1.5,

1 W

-

1 1 1 1 1 1 1 11 [ 1 1 1 1 1 1 1 1 1 1 1 1

: • •

ZrC) 7

10'

10-10

j

IZn(0E)2]s

A

E

\ J ^ .

Bz HDD Zn(0E)2

2.26 mol kg-M

:

Q

•

•

• 10'

. . . I . . . . I . . . . t.

0.4 0.2 m I mol kg"

0.6

Fig 3. Diffusion coefficients for the Zn(II) complex and water in chloroform and methanol systems depending on the complex concentrations.

• •

in-ii

0

10

1

20

30

..y..... 40

50

60

Fig 4. Diffusion coefficients for the Zn(II) complex and water in the water/benzene systems depending on the water content. {W^ = [H20]/[Zn(II) complex])

34

The structures of the microemulsions were directly observed by TEM. Figure 6 shows typical cases of TEM photographs for the Zn(OE)2Cl2/H20/benzene system where the wei^t ratio of the Zn(OE)2Cl2: benzene is 1:1. In thisfigure,at 15 wt % water content (1), spherical particles with diameters of 25-30 nm were uniformly dispersed. Those particles must be water-in-oil (w/o) microemulsions having water pools in the cores. The TEM texture changed at 20 wt % water content (2) to sponge phase with water channels. For a solution with 40 wt % water content (3), the TEM photograph displayed typical texture of bicontinuous phase which has benzene and water domains. A solution with 30 wt % water content shows a mixture of sponge and bicontinuous phases. Bicontinuous phase was observed even for a 1.5 : 1 solution of the Zn(OE)2Cl2: benzene ratio with 50 wt % water content.

S! io-«

[

A

^

j

A

1

A Jk.

m / moi kg''

E

10-^Oh

HDO Pd(0E)2 HDO Pd(0E)2

• •

0.15 J 1.04

]

Z«(OE)i

Q

r

11

•

•

•

1

V60

.\-A.„>..,A...

30

40

50

6 0 H:0

Fig 5. Diffusion coefficients for the Pd(II) complex and water in water/chloroform system depending on the water content (WQ),

Fig 6. Ternary solubility diagram for the Zn(II) complex/water/ benzene system and the TEM photogr^hs at the respective (1-3) compositions on the phase diagram.

REFERENCES 1. M. lida, A. Yonezawa, and J. Tanaka, Chem. Lett., (1997) 663. 2. M. lida, T. Tanase, N. Asaoka, and A. Nakanishi, Chem. Lett., (1998) 1275. 3. M. lida, H. Er, N. Hisamatsu, T. Tanase, Chem. Lett., (2000) 518. 4. D. A. Jaeger, V. B. Reddy, N. Arulsamy, D. S. Bohle, D. W. Grainger, and B. Berggren, La/igmw/r, 14(1998)2589. 5. X. Lu, Z. Zhang, and Y. Liang, Langmuir, 12 (1996) 5501; ibid., Langmuir, 13 (1997) 533. 6. Y. Ikeda, T. Imae, J. C. Hao, M. lida, T. Kitano, andN. Hisamatsu,Langmuir, 16 (2000) 7618.

Studies in Surface Science and Catalysls 132 Y Iwasawa. N Oyama and H Kunleda (Edltors) (c1 2001 Elsevier Science B.V All rights reserved

35

Kinetics of Lamellar to Gyroid Transition in a Nonionic Surfactant System M. Imai,

A. Kawaguchi, A. Saekia, K. Nakaya, T. Katob, and K. ItoC

Faculty of Science, Ochanomizu University, Bunkyo, Tokyo 112-0012, Japan aDepartment of Physics, Keio University, Yokohama 223-8522, Japan bGraduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan %stitUte of Applied Biochemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan Kinetics of Lamellar to Gyroid Transition in a Nonionic Surfactant System has been investigated by means of a small angle x-ray scattering (SAXS) technique. For large AT ( AT=T-TL,, T: temperature, TLG:lamellar to gyroid transition temperature) in the lamellar phase, the SAXS profiles can be described by a structure factor for undulation fluctuation lamellae. Approaching the temperature to the TLG,an excess diffuse scattering grows at lower Q (Q: magnitude of scattering vector) side of the first lamellar peak. This diffuse scattering arises from the modulation fluctuation of lamellar layer. At the T,, the PFL transformed to the gyroid phase through a transient ordered structure having a rhombohedra1 symmetry. 1. INTRODUCTION

One of the most fascinating properties of surfactantfwater systems and block copolymers is their ability to form a variety of ordered mesophases, such as hexagonally ordered cylinders (C), lamellae (L), and a gyroid (G) structure having a bicontinuous cubic network with Is3,, symmetry. The similarity of phase behaviors for surfactant/water systems and block copolymers suggests universal nature of ordered mesophases originated from their incompatibility effects. Hence the behaviors of ordered mesophases have been the subject of the extensive experimental and theoretical investigations. An important target of the order-order transition (OOT) studies is to reveal the kinetic pathways between the ordered mesophases. From experimental point of view, OOT’s proceed by a nucleation and growth mechanism [l]. Matsen [2] showed the nucleation and growth process for C to G transition on the basis of self consistent mean field theory. However some pre-transition structures are observed in OOT’s, such as a hexagonally perforated layer (HPL)phase [3] in L to G transition of block copolymers, an intermediate phase [4] having Rhombohedra1 symmetry between L and G phases,

36 and a characteristic fluctuation mode predicted by Laradji et al. [5], in C to bodycentered-cubic spheres phases of a tribiock copolymer [6]. Then it is quite meaningful to elucidate the stability of the fluctuations around the equilibrium ordered mesophases prior to the OOT's. In this report we reveal fluctuations of the L phase prior to the L to G transition in the surfactant/water system using a small angle x-ray diffraction (SAXS) technique with synchrotron radiation source and newly developed large area charged coupled device (CCD) detector. 2. EXPERIMENTS We examined the L to G transition of a Cj^Ev/DjO system [7]. The samples containing 46, 50, 52, 55, and 60 wt% of C,6E7 were sealed in a glass vial. For homogenization we annealed the sample for 3 hours at about 55°C and then held it at room temperature for 21 hours. This annealing procedure was repeated about one week and then the samples were transferred to a temperature control cell for SAXS measurements. Standard sample dimensions were diameter of 3.0 mm and thickness of 1.0 mm, which brings polycrystalline L phase. In order to obtain highly oriented L phase, we used thin sample cells with a thickness of 50 |im. The orientation of the L phase was checked by polarized optical microscope observations. SAXS measurements were performed using BL-15A instrument [8] at the photon factory (PF) in the high energy accelerator research organization (KEK). The samples were heated from room temperature (C phase) to 67 "C (L phase) and then annealed isothermally (±0.1 X ) for 100 min to reduce the sample history. After the isothermal annealing, the samples were cooled from 67 X to the TLG with stepwise manner and these processes were followed by SAXS measurements. 3. RESULTS AND DISCUSSIONS First we show brief features of the L to G transition of 55 wt% C,6E7/D20 system obtained from the polycrystalline samples. We plot development of one dimensional scattering profiles as a function of temperature in Fig. 1. At 66.1 °C, two Bragg peaks can be observed at g = 0.098 A*' and 0.19 A'', indicating stacked lamellar structure. The first lamellar peak is composed of a sharp Bragg peak and diffuse asymmetric tail spread around the Bragg peak. The diffuse tail originates from the undulation of lamellae and can be described by the Caille correlation function [9]. From fitting of observed profile by the Caille function, we obtained a bending modulus K=0.7 kBT. Decreasing the temperature to the T^Q, peak positions shift to higher Q side and diffuse shoulder appears at |g=0.09 A'. This new diffuse shoulder can not be explained by the Caille correlation function, indicating the existence of another type of fluctuations. Approaching the temperature to the JLG, the intensity of the excess diffuse scattering increases with keeping the peak maximum position and is reversible against the temperature. At 47.5 °C, in addition to the lamellar peaks the scattering profile shows apparent new peaks at g = 0.093, 0.107, 0.15, 0.16, and 0.19 A*'. Holmes et al. investigated phase behavior of CiEj/D20 systems and reported intermediate phases between C and L

37 phases or G and L phases. They attributed the intermediate phases to rhombohedral (R) structures. The intermediate phase having space group of R 3m provides the most likely structure, which explains the diffraction pattern of the transient structure observed in this study. It should be noted that the R structure is not an equilibrium structure but a transient structure which transforms to the G phase spontaneously during isothermal annealing. When we decreased the temperature to 43.8 °C, the scattering profile changed to another pattern. The new diffraction profile agrees well with that of the G structure (Ia3d). Thus the L to G transition proceeds by lamellae-»fluctuating lamellae-^R structure-»G structure. Hereafter we focus our attention to fluctuations in the lamellar structure prior to the L to G transition. Recently Saeki et al. [10] developed a new computational simulation scheme to obtain the equilibrium structure of ordered mesophases. Using this scheme, they found perforated lamellae close to the T^ as shown in Fig. 2. The channels in the lamellae fluctuate with time and do not show characteristic spatial symmetries such as hexagonal symmetry observed in block copolymers (HPL phase [3]). Thus, this structure is not the HPL phase but perforation fluctuation layer (PFL) structure. They showed that the PFL gives a diffuse peak appears in SJ^Q) (scattering function in lamellar plane) having its peak position at slightly lower Q side of the first lamellar peak. In order to confirm the validity of PFL model we performed scattering experiments for oriented lamellae, which reveals behavior of in-plane and out-of-plane fluctuations. Fig. 3 shows the evolution of the 2D scattering patterns, Si.{Q^,Qy), during the cooling process from the L phase to the G phase when the x-ray beam irradiates perpendicular to the lamellar plane. The scattering pattern at 65.1°C (Fig. 3 (a)) is monotonic without Bragg peaks confirming that the x-ray beam irradiates perpendicular to the lamellar plane. Decreasing the temperature to the TLQ, a diffuse isotropic scattering ring appears (Fig 3 (b)) and grows, indicating the development of the in-plane density fluctuations. At 47.6 X hexagonal diffraction spots (corresponding to diffraction spots from {300} crystal planes) of the R structure appear with hexagonally symmetry diffuse fragments (Fig. 3 (c)-(d)). Further anneahng at 47.6 X the scattering pattern transforms to the typical G phase pattern (Fig. 3 (e)-(f)). Here it should be noted that diffraction spots from {211} crystal planes are appears at the diffuse peak position of the R structure. In conclusion. At high temperature region in the L phase the amplitude-modulation fluctuated lamellar structure is observed. Modulation fluctuations increase their amplitude as the temperature approaches T^ and finally develop to the stable PFL. At the TLG, first the transient R structure appears and then transforms to the G phase. It is quite interesting to note that (110) peak of the R structure appears at the diffuse scattering peak position of the PFL structure and (211) peak of the G phase grows at the diffuse scattering peak position of the R structure. This indicates that the fluctuations around the equilibrium ordered mesophases play an important role in the OOT's.

38

(b)49.4'C Qy (A-l) 0.2

• \

\

Sit .;

^W^.J 0.2

(d)47.6'C

0.24

Qy (A-^) 0.2

Fig. 1. Evolution of SAXS profiles from L to G phases as a function of temperature.

-0.2]

- 0:

0.0 0.2 Qx (A-J)

(e)47-6°C lOmin

- 0.2

0.0 0.2 Qx (A-l)

(f)47.6'C13min o.v (A-i) 0.2 I

Fig. 2. Perforating lamellar structure obtained in Saeki's simulation.

Fig.3. Evolution of 2D scattering patterns 5l(Gx,Cy) from the L phase to the G (a) 65.1 X , (b) 49.4 "C, (c) 48.3 X , and (d) ~ (f) time evolution of scattering patterns at 47.6 'C.

REFERENCES 1. M. Clerc, P. Laggner, A.M. Levelut, and G. Rapp, J. Phys. II5, 901, (1995). 2. M.W. Matsen, Phys. Rev. Lett. 80, 4470 (1998). 3. D.A. Hajduk, et al., Macromolecules 30, 3788 (1997). 4. J. Burgoyne, M.C. Holmes, and G.T.T. Tiddy, J. Phys. Chem. 99, 6054 (1995). 5. M. Laradji, A.-C. Shi, R.C. Desai, and J. Noolandi, Phys. Rev. Lett. 78, 2577 (1997). 6. QY. Ryu, M.E. Vigild, and TP. Lodge, Phys. Rev. Lett. 81,5354 (1998). 7. T. Kato, N. Taguchi, T. Terao, and T. Seimiya, Langmuir 11, 4661 (1995). 8. Y. Amemiya, et al., Nucl. Instr. and Meth. 208, 471 (1983). 9. A. Caille, C.R, Acad. Sci. Ser. B 274, 891 (1972). 10. A. Saeki, and F. Yonezawa, Prog. Theor. Phys. Suppl. in press.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyamaand H. Kunieda (Editors) P 2001 Elsevier Science B.V. All rights reserved.

39

Efficiency boosting by amphiphilic block copolymers in microemulsions: Dependence on surfactant and oil chain length R. Strey, M. Brandt, B. Jakobs and T. Sottmann Universitat zu Koln, Institut fur Physikalische Chemie, Luxemburger Str. 116, D-50939 Koln, Germany We examine the enhancement of the solubilization capacity of medium-chain surfactants in microemulsions of ternary base systems water - n-alkane - CjEj by block copolymers of the poly-(ethylenepropylene)-co-poly(ethyleneoxide) (PEP-PEO) type. The effect is an enormous increase of the swelling of the middle phase microemulsion by water and oil. The magnitude of the effect depends slightly but systematically on the chain length of the surfactant forming the base system and on the chain length of the alkane. Interestingly, the less efficient the base system the larger the boosting effect. Furthermore, the lamellar phase, which usually develops as surfactants become more efficient, is suppressed, the more the less efficient the surfactant of the base system. 1. INTRODUCTION In this paper we further investigate the efficiency boosting effect of block copolymers in microemulsions^'^. In order to appreciate the magnitude of the effect let us recall that in microemulsions, which are thermodynamically stable and macroscopically isotropic mixtures of at least three components water, oil and surfactant, the surfactant forms an extended interfacial film separating water and oil on a local scale. We previously determined the elastic properties of the amphiphilic film for suitable systems^"^ There the correlation between the state of highest efficiency and the bending constants for a variety of nonionic surfactants was determined^. It is well-known that increasing the hydrophobic chain length of the surfactant the amount of surfactant needed to form a one-phase microemulsion is systematically lowered, i.e. the efficiency increases. Also, one generally observes that concomitantly the lamellar phase is stabilized^. We have discovered and reported recently*'^ how to increase the efficiency of surfactants by adding block copolymers while reducing the range of stability- of the lamellar phase. Even more recently an explanation of the effect in terms of an enhancement of the saddle-splay modulus of the film was given^. While mixtures of two surfactants of comparable chain length show small synergistic effects in microemulsions^, adding an amphiphilic block copolymer to a conventional microemulsion system leads to a large efficiency increase already by traces of polymer. The oil and water excess phases are progressively incorporated in the surfactant-rich middle phase which thereby increases in volume. Interestingly, the efficiency boosting experiments can be performed at constant temperature because the hydrophilic-lipophilic balance of the base system is not or only little affected^. Here we report how the observed

40

efficiency boosting effect depends on the surfactant chain length and the oil chain length while keeping the block size of the amphiphilic block copolymer constant. 2. EXPERIMENT 2.1. Phase Diagrams The phase diagrams are determined using thermostated water baths with temperature control up to 0.02 K. The sample composition is given by the oil in (water plus oil) mass fraction a = me / (mA + me), the overall mass fraction of the surfactant (or surfactant plus polymer mixture) y = (mc ^mo) / (mA + me + mc +mD) and the mass fraction of the polymer in the surfactant/polymer mixture 5 = mp / (mc + mp). In this study all samples were prepared at an oil / (water + oil) - volume fraction of (|) = 0.5. 2.2. Materials The n-alkanes were either from Sigma Aldrich (Steinheim, Germany) or Merck (Darmstadt, Germany) with a purity > 99%. The alkylpolyglycol ether surfactants (CjEj) were obtained from Fluka (Neu-Ulm, Germany) and Bachem (Bubendorf, Switzerland) with a purity > 98 %. All substances were used without further purification. The amphiphilic block copolymer is poly-(ethylenepropylene)-co-poly(ethyleneoxide), abbreviated PEP5-PE05, where the approximate molar masses of the blocks are 5 kg/mol. The polymers were synthesized by a two-step process as described elsewhere^"''. A narrow M^/Mp ratio of 1.02 was obtained. 3. RESULTS AND DISCUSSION 3.1. The ternary base systems The phase behavior of the ternary water - n-alkane - CjEj systems has been described in various connections^^"^^. A useful way to characterize these systems are vertical sections through the phase prism at constant water/oil-ratio. In these sections the coexistence curves show the well-knovm "fish" diagram. At low temperatures a microemulsion of o/w type coexists with excess oil (denoted by 2). At high temperatures a microemulsion of w/o type coexists with excess water (2). At lower surfactant concentrations the three phase body occurs (3), at higher surfactant concentrations the one phase region appears (1). Such a "fish" for the water - n-octane - CgEa system is depicted by the hollow circles in Fig. 1. The minimum surfactant concentration for complete solubilization of water and oil, that is where the three-phase and one-phase region meet, is denoted by y at temperature f ^^. This point is referred to as X-point and is a useful measure for the efficiency of a surfactant. The lower Y the more efficient a surfactant is.

41

30

25 [

U o H

" '^' - ^^^-^*^^^-^^v .^

20

15

10

0.00

0.05

0.10

0.15

0.20

0.25

Y

Fig. 1 Section through the phase prism at equal volumes of water and n-octane ((t)=0.5). The well-known "fish" is shown for water-n-octane-CgEa as hollow circles. The effect of adding the amphiphilic polymer PEP5-PE05 leads to an efficiency increase, a shift to smaller y (fiill circles) at unchanged hydrophilic-lipophilic temperature. 3.2. Efficiency boosting by the amphiphilic block copolymer The striking phenomenon of adding the polymer PEP5-PE05 is demonstrated by the full circles in Fig. 1. These mark the fish-tails for increasing 5. Addition of polymer leads to a reduction of y from 0.19 at 6=0 to 0.069 at 6=0.10. Proceeding to 6=0.15 the minimum amount of surfactant plus polymer to form a one-phase microemulsion drops to y =0.019. Remarkably the addition of PEP5-PE05 does not lead to the formation of the lamellar phase in the fish tails presented in Fig. 1. Even for the most efficient fish tail (6=0.15) the lamellar phase does not appear up to y=0.08, the highest surfactant concentration we checked. Only strong streaming birefringence is observed. In spite of the small quantities of polymer added a striking efficiency enhancement is achieved. Extending the measurements to yroplet of LC dispensed at the bottom is pumped by application of -0.3 V to the bottom electrode and 0.3 V to the left electrode.

53

pair of electrodes caused the LC droplets to be pumped between the two electrodes. The velocity of the droplets was controlled by the magnitude of the potential applied to the electrodes. The oxidation and reduction of IV was also used to demonstrate flow of LC droplets across an unconfined surface.

t-Os

mmmm t = 10s

Because local changes in the surface tension of aqueous solutions can give rise to localized imbalances of force at the threephase contact line of liquid supported on a surface and thereby place a liquid into motion, we have explored the use of ferrocenyl surfactants in strategies for patterned wetting and dewetting of aqueous solutions on Figure 3: top view of dewetting of an surfaces. We illustrate this aqueous film of 0.3 mM II (0.01 M capability here by using ferrocenyl Li2S04, pH 1.3) supported on surfactant to form a 2-dimensional microscope slide patterned with a mesh array of droplets on the surface of of electrodes (dark region). Etewetting glass (Figure 3). The glass was was induced at the top left comer of the patterned by evaporating 50 A of microscope by application of 0.5 V (vs. titanium and 500 A of gold SCE) to the electrode. The receding film through a micromachined leaves droplets on the regions of glass. aluminum mask. The surfaces The image was illununated from Sie were made energetically lower right side causing shadows to homogeneous by immersing into a form diagonal lines across the droplets. solution of 0.9 mM 11mercaptoundecanoic add and 0.1 mM hexadecyl mercaptan for 30 minutes. After application of a thin film of aqueous solution of i r , an oxidizing potential (0.5 V) was applied to the array of electrodes. The aqueous solution dewets the gold electrodes leaving droplets on the glass. Without any applied potential, no patterned dewetting was observed. The patterned dewetting can be repeated on the same surface by reapplying a fresh film of aqueous surfactant solution. Whereas gradients in surface tension caused by changes in the oxidation state of i r drive the phenomena shown in Figure 1, the patterned dewetting of solutions of W is caused by electrochenucally induced changes in the contact angle of the solution on the surface. Surface plasmon reflectometry measurements suggest that

54

electrochemically induced desorption of surfactant from the solid-liquid interface plays a central role in the phenomena. An increase in the contact angle leads to a net force on the contact line causing the solution to dewet the electrode. In other work, we have shown that spreading can be induced by electrochemical control of gradients in surfactant concentration near the contact line. In conclusion, the results summarized above demonstrate the use of ferrocene-based surfactants in combination with electrochenucal methods to achieve both spatial and temporal control of the adsorption of surfactant at interfaces. This capability provides new ways to control interfadal phenomena in surfactant systems, including Marangoni effects and the spreading and wetting of liquids on surfaces. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.

B.S. Gallardo, M.J. Hwa, N.L. Abbott, Langmuir, 11 (1995) 4209. D.E. Bennett, B.S. Gallardo, N.L. Abbott, J. Am. Chem. Soc. 118 (1996) 6499. B.S. Gallardo, K.L. Metcalfe, N.L. Abbott, Langmuir, 12 (1996) 4116. B.S. Gallardo, N.L. Abbott, Langmuir, 13 (199^ 203. B.S. Gallardo, V.K. Gupta, F.D. Eagerton, L.I. Jong, V.S. Craig, R.R. Shah, N.L. Abbott, Science, 283 (1999) 57. N. Aydogan, B.S. Gallardo, N.L. Abbott, Langmuir, 15 (1999) 722. J.Y. Shin, N.L. Abbott, Langmuir, 15 (1999) 4404. T. Saji, K. Hoshino, I. Yoshiyuki, G.J. Masayuki, J. Am. Chem. Soc. 113 (1991) 450. T. Saji, K. Hoshino, S. Aoyagui, J. Am. Chem. Soc. 107 (1985) 6865.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) cc) 2001 Elsevier Science B.V. All rights reserved.

55

Droplet microemulsion and telechelic polymer: linear rheology and flow instability at high shear. G. Porte, M. Filali, E. Michel, J. Appell, S. Mora, E. Sunnyer and F. Molino Groupe de Dynamique des Phases Condensees, Case 026, Universite MontpelUer II 34095 MontpelUer Cedex 05, France Our purpose is to examine in detail the flow behaviour of model transient networks. Such a network is obtained from an o/w droplet microemulsion into which we incorporate a hydrophobically end capped hydrosoluble polymer. At high enough droplet and polymer concentrations, the system exhibits viscoelastic behaviour with quasi maxwellian stress relaxation. The variations of the elastic modulus and terminal time at the percolation threshold are discussed in the light of the Tanaka-Edwards theory: droplets rearrangements after the escape of a sticker are essential. Under steady shear, a sharp flow instability is observed. We show that it arises from a fracture like formation of a lubricating layer at the surface of the shear cell. INTRODUCTION Temporary networks are intuitivelly appealing examples of viscoelastic materials and a lot of theoretical effort have been spent to account quantitatively for their rheological behaviour both in the linear regime and under high deformation [1,2]. The finite instantaneous elastic modulus G(0) arises from the existence of junctions capable to sustain the stress while the terminal time T/^ is related to the finite residence time of the extremities of the strands into the junctions [3]. The most refined theories to date rely however on two simplifying assumptions [2]: i) the deformation of the network is homogeneous at all scales, (affine to the macroscopic deformation applied); ii) once one end of an active strand snaps off a junction, it definitely forgets the strained state of the network. These theories predict quasi maxwellian stress relaxation after step strains of moderate amplitude (linear regime) and shear thinning behaviour at high rates under steady shear (due to the shorter residence time of strands submitted to high tensions). These predictions agree qualitatively with the observations. However, although reasonnable for densely linked networks, the above mean field assumption becomes questionnable for tenuous network close to the percolation threshold. Moreover, the flow curve in steady shear often show up an unexpectedly sharp drop of the stress. To examine these points, we study transient networks in which the average number density and ftinctionnality of the junctions can be controlled separately. They are obtained from an o/w droplet microemulsion into which we incorporate a hydrophobically end capped water soluble polymer. The microemulsion involves TXlOO and TX35 as non-ionic surfactant, the oil is decane and the proportions are chosen so to fix the size of the droplets (82A radius checked by neutron scattering) at all concentrations. The telechelic polymer is a 10k POE end grafted

56 with C18H37. The endcaps stick to the oil droplets with a residence time (of the order of Is) controlled by their degree of hydrophobicity. The droplet concentration determines the number density of the junctions while the concentration of added polymer (number r of stickers per droplet) determines their average fimctionnality. In section 1 we report on the percolation behaviour from step strain experiments. Comparisions with simple numerical simulations show that droplets reorganization due to the balance of strand tensions play a crucial part in the stress relaxation. In section II we characterize the flow instability under steady shear and show that its origin is located near the walls of the shear cell. 1. LINEAR RHEOLOGY: In all samples, the droplet volume fraction is 10%. Their average distance is thus of the order of the end to end distance of a free 10k POE coil: so bridging is easy. Rheological measurements are performed with a strain controlled rheometer (Rheometrics RFSII). Figure 1 shows typical stress relaxation after a moderate step strain. The behaviour is close to Maxwell; the fit with a slightly stretched exponential is very good:

l U

^ 1 I I I I I I I I I I I I I I ! I I I j I I I I i I 1 ^

lOOOi £

o

100 10

0.1 0

0.49

0.97 time (s)

1.5

Figure 1: Stress relaxation for the 10% droplet sample with r=18 stickers per droplet

0.85 X G{t) = a(t)/Yo = G(0)exp(-(r/T^)^°^)

(1)

allowing an accurate determination of G(0) (=2300Pa) and of T/? (= 0.137s). The stress relaxation as function of r is fitted for all sample with expression (1). Both G(0) and T/^ decrease upon decreasing r and vanishes below a finite threshold value rp.

57 I I I 11 I I I I I I I I I I I I I I I I •

I I

2000 CO

6

1000

0

'

0

'

•

'

' ^ ^ • ^ '

5

I

I

I

•

I

10

I

I

I

15

I

I

'

I

I

20

I

I

I

25

r Figure 2: G(0) as function of r at 10% fraction of droplets

Figure 2) illustrates the percolation behaviour of G(0) at r [4]. The continuous line is a fit with the power law: G(0,r) = Go(r-rJ^

(2)

which gives rp= 4.23 for the threshold and ^ = 1.42 for the exponent. Of course a percolation pattern is not unexpected: afiniteminimum connectivity density must be exceeded so that an infinite connected cluster builds up capable of transmitting the torque all through the gap between the mobile and the fixed wall of the shear cell. We note however that these values do not coincide with those reported in the litterature [5] for bond percolation calculated on simple cubic lattice (threshold about 1.5 and exponent 1.7). But in our situation, some polymers loop on the same droplet and therefore do not contribute to the stress. Moreover, neighbouring droplet may be linked by two or even more polymers strands. These specific features may account for the discrepancies. A mean field simplification is usually postulated at the starting point of the current interpretation of the stress relaxation: macroscopic deformations applied to the sample are assumed to propagate homogeneously at all scales into the material. Immediately after the application of a step strain, the initially isotropic distribution of the nodes is affinely convected so that, depending on their initial orientation with respect to the shear direction, threads are stretched or compressed compared to their initial length. The resulting anisotropic distribution of tension is at the origin of the intantaneous elastic stress a(t = 0). As time goes on, stickers randomly escape from the droplets with a characteristic time (the residence time: T^.^^). Each time a sticker escapes, the tension or compression of its thread vanishes immediately and so does its contribution to the total stress. Of course, the escaped sticker will soon recombine with another droplet, but it will do so in an isotropic manner and therefore no longer participate to the stress history: this is the second simplifying assumption in the current interpretation. In this primitive

58

description, ait) is simply proportional to the number r(t) of stickers per droplet that have not yet escaped at time t and therefore are still under tension or compression. Since the escape is a random process, we expect: G(r)/G(0) = r(t)/r = exp(-r/r,,,)

(3)

that is a Maxwell relaxation with r^^^ as characteristic time. The experiments confirm a quasi-Maxwellian stress relaxation. But, according to the above mean field description, we would expect G(0,r)ocr in contradiction with the singular behaviour of G(0,r) at r^. Clearly, not all the threads deform affinely to the macroscopic strain tensor: threads which belong to finite size clusters as well as dangling threads decorating the infinite cluster are indeed not elastically active. Only the threads which belongs to the skeleton of the infinite cluster are active. In order to remove the assumption of homogeneous affine deformation, one could start from the r dependence of G(0) as fitted from the experiment (expression (2)) and write: Git) = G(0,r(r)) = Go(r(r) - r^)^

(4)

the modulus Git) at time / is so taken identical to the instantaneous modulus of a sample having a degree of connectivity equal to r(r). Assuming again the stickers to escape at random: r(r) = rexp(-r/r^^J

(5)

one gets: Git) = Go(rexp(-r/T,,,) - r^)^

(6)

Proceeding so, we extend the effect of the nonhomogeneous connectivity of the network evidenced in the intantaneous elastic response to all the later stages of the stress relaxation. However expression (6) is in obvious contradiction with the quasi-Maxwellian relaxation found experimentally: all stress in (6) is totally removed after a finite time t = T^^^ln(r/rp) and it cannot coincide with the observed stretched exponential decay. Therefore, correcting for the non-homogeneous, non-affine deformation alone is clearly not sufficient. We must consider the second explicit assumption of the current theories -namely that escaped threads no longer participate to stress history. A given droplet, has a mechanical equilibrium position where all tensions of the attached threads compensate. Each time a sticker escapes, the tension balance is broken and the droplet moves to a new equilibrium position within a typical time certainly much shorter than the residence time of the stickers. Therefore, at all stage of the stress relaxation, the position distribution of the droplets rearranges so insure instantaneously mechanical equilibrium. As mentioned above, a sticker escaped at time t inmiediately recombines with another droplet but after having relaxed its initial tension: the new junction formed bears no tension. However as time proceeds, the relative positions of the droplets changes so that a tenseless thread at

59 time t may well find itself stretched or compressed (with respect to the equilibrium length distribution) at time t' >t. Therefore, due to the rearrangement of the droplets positions, a sticker having escaped early from the initial droplet, will nevertheless participate to the later stages of the stress relaxation. We believe that tensions arising after recombinations and equilibrations explain the regular character of the stress relaxation at long time. Numerical simulations on a 2D distribution of beads and springs are performed and support our interpretation.

2. FLOW INSTABILITY AT HIGH STEADY SHEAR RATES

600

CO CO

300 h

(D

rate (s'"*)

Figure 3: Stress versus rate for the 10%r=21 sample The flow curve of the sample with 10% droplet fraction and r= 21 under steady shear rate is shown in figure 3). It is obtained with a titanium cone and plate; the cone angle is 0.02rad. Special attention is paid to make sure that all data points correspond to true steady state (slow transients are observed close to the discontinuity). There is two regimes with a sharp drop in stress at the cross over. The low shear rate regime is close to Newtonian with a viscosity % = 270 Pa.s. The discontinuity occurs at a rate Yinst"^ ^-^^^ ^^^ ^ stress 0^^^^^= 400 Pa. Between 1.6s"^ and 3s"\ we find a range where the stress is a decreasing function of the rate. At still higher rates, we recover a regime where the stress increases linearly with the rate but according to the unexpected form: (7 = 0"y

+ n/^r

(7)

The positive apparent "yield stress" Oy (80 Pa) is reminiscent of a Bingham behaviour and the effective viscosity 7]/^^= 23 Pa.s is much lower than % .

60 Homogeneous flows are unstable in the range where the stress decreases as the rate increases. The drop in stress then suggests the onset of a fracture-like non-homogeneous flow pattern: a lubricating layer of low viscosity forms above Yinst- ^^ such fracture were to appear at any position in the gap, additionnal fractures would occur each time the stress exceeds Oif^st- This is not the case on the upper stable branch in figure 4. So, the fracture occurs at a special position in the gap: that is at the wall of the shear cell To check this point, we established the flow curve (figure 4) using different aluminium tools: sand blasted cone with 1.5° angle, polished cone with 1.5° again, polished cone with 3° angle. Considerable differences are actually observed for the flow instability (see figure 4 for an illustration). 300

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I M [ I I I I

i sand blasted 1 OH

150

Figure 4: different surface roughnesses To sum up: -the slope of the upper stable branch {7]^^) only depends on the cone angle (roughly proportional) but not on the surface roughness (figure 4). -on the other hand the onset of the instability (cr,^^^; and Yinst)^ ^^ ^^^^ ^^ ^^^ y'\Q\d stress Gy, decrease strongly when the surface is smoother. -of course the viscosity in the Newtonian low rate regime is invariant. So the stress drop discontinuity involves a shear induced transformation of the material in the vicity of the shear cell surface. Note that the stress pattern is different from that observed in case of simple sliding at the interfaces. Specially intriguing is the yield-like aspect of the high shear regime (cr^). We currently study the influence of the chemical nature of the surface (more or less hydrophobic) on the onset of the instability in order to elucidate the adhesion of the network onto the shear cell wall. REFERENCES [1] M. S. Green and A. V. Tobolsky, J. Chem. Phys.,U, (1946), 80. [2] F. Tanaka and S. F. Edwards, Macromolecules, 25, (1992), 1516. [3] T. Annable et al, J. Rheology, 37, (1993), 695. [4] H. Bagger-Jorgensen et al, Langmuir,U, (1997), 4204. [5] D. Stauffer, Introduction to percolation theory, Taylor & Francis Pub, London, (1985)

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) •c 2001 Elsevier Science B. V. All rights reserved.

61

Synthesis and micelle formation of fluorine-containing block copolymers Kozo Matsumoto*, Taku Kitade, Hiroaki Mazaki, Hideki Matsuoka, and Hitoshi Yamaoka^ Department of Polymer Chemistry, Kyoto University, Kyoto 606-8501, Japan ABSTRACT: Fluorine-containing block copolymers composed of poly{2-(2,2,3,3,3pentafluoropropoxy)ethyl vinyl ether)} (polyPFPOVE) and poly(2-hydroxyethyl vinyl ether) (polyHOVE) were synthesized and their micelle formation in water was investigated. The block copolymers were prepared by sequential polymerization of PFPOVE and 2-acetoxyethyl vinyl ether (AcOVE), followed by hydrolysis of the acetyl-protecting group. The surface tension of the block copolymer solution decreased to ca.32 mN/m. The experimental data of the small-angle X-ray scattering (SAXS) measurement of 1 wt% aqueous polymer solution were well-reproduced by the calculated scattering curves for core-shell micelle models. 1. INTRODUCTION Fluorine-containing block copolymers are a new series of polymer materials.'" They have attracted much attention because of the unique properties of fluorinated segments such as low surface energy, high contact angle, reduced coefficient of friction, high biocompatibility, and lipoand hydrophobicity. We have recently reported the synthesis and the micelle formation of fluorinecontaining amphiphilic block copolymer, poly(2-hydroxyethyl vinyl ether)-/7/d?c/:-poly[2(2,2,2trifluoroethoxy)ethyl vinyl ether] (poiy(HOVE-6/(9c/:-TFEOVE)).' In this study, we synthesized a new amphiphilic block copolymer with a higher fluorine content, that is polyiHOVE-blockPFPOVE), and examined its surface activity and micelle formation. 2. EXPERIMENTAL SECTION Measurements. Gel permeation chromatography was carried out in chloroform on a JASCO GPC-900 equipped with four polystyrene gel columns (Shodex K-802, K-803, K-804, and K-805). 'H NMR spectra were recorded on a JEOL GSX 270 spectrometer in CDCI3. Surface tension was measured on a CBVP-Z (Kyowa Interface Science Co., Ltd.) using a Pt plate in full automatic mode. Small-angle X-ray scattering (SAXS) of polymer solution was measured using a Kratky-type camera manufactured by Rigaku Corporation installed on a rotating anode X-ray generator and a position-sensitive proportional counter.

^Present address: Department of Materials Science, School of Engineering, The University of Shiga Prefecture, 2500, Hassaka, Hikone, Shiga, 522-8533, Japan

62 Synthesis of Poly(HOVE-^/oc/c-PFPOVE). Polymerization was earned out under nitrogen by addition of /z-butyl vinyl ether-HCl adduct and ZnCK into a mixture of PFPOVE and in methylene chloride at -40 ""C. After PFPOVE had been converted, AcOVE was added, and the mixture was allowed to warm at -20 °C. The polymerization was quenched with methanol containing ammonia The mixture was washed with water, extracted with diethyl ether, and concentrated to give poly(AcOVE-Z?/oc/:-PFPOVE). The acetoxy groups of the polymer were hydrolyzed by treatment with aqueous sodium hydroxide in 1,4-dioxane. Removal of impurities by dialysis in water followed by freeze drying gave poly(HOVE-6-PFPOVE). MJM„ values were determined by GPC with a polystyrene standard calibration for poly(AcOVE-/7/(9ci(:-PFPOVE). The number-average degrees of polymerization of AcOVE segment (m) and PFPOVE segment (n) were determined by 'HNMR. Data Analysis of SAXS Measurements. model were calculated as follows:

The theoretical profiles for a spherical core-shell

I(q) =/np[47c/3 • R^^p.-p^WR^q) + 4n/3 • R,^(p,-i)o)0.3 T.

When a magnetic field was parallel to the lipid membrane,

no magnetic effect was observed, suggesting that no ion flow would be directly affected by the Lxjrentz force. We assume that magnetic fields should modify the ^parent fixed charge density X of the membrane.

The features in the experimental magnetic responses of "^ and R seem to be

consistent with each other via <j)X within the theory[7].

Fig.2 shows that the estimated X

changed with magnetic field through a minimum {^X^J at H^.

These trends in Fig. 2 may be

brought about by the molecular orientation in a domain, which leads to changes in the molecular density at the membrane surface.

When a lipid molecule tilts under a magnetic field, the

occupied molecular area increases monotonically with tilt angle and thus charge density would also decrease monotonically with magnetic field. On the other hand, with increasing a tilt angle, the hydrocarbon/water interface at the membrane surface should increase and destabilize the tilted structure.

Thus, the critical tilt angle must exist.

Then, one possible way to increase charge

density at higher magnetic fields would be to introduce membrane deformation in a plain

o

noneOh) A 10 inol% benzene (3h) A 20 niol% benzene (3h) D lOmoHb atthnceae (3h) 20mol% anUutcene (3b) nooedOOh) V 20 niol% benzene (lOOh) T 20mol% uUncene (lOOfa) O 10 nK>l% pyrene • 20 ntol% pyicne

|

•

•

MagnetoAision

• ••^.y o 12 16 Hll Figure 3 Variations of radiiB r ( # ) of IFPC liposomes and changes in membrane potential AV'(O) of a black lipid membrane at 318K with a steady magnetic field intensity.

i^

f

Magnetodivision i» 4 .

800 /nm

Rgur« 4 Comparison between experimental and n values. Theoretical for p = 20 nm: gray region. Experimental: all symbols.

82 surface. Under higher magnetic fields, membrane deformation out of a plain surface may be expected so as to relax the orientational defects among domains having different orientation at a tilt angle. Thus, we may expect great changes in membrane potential. In fact, the membrane potential changed markedly with magnetic field more than 12 T (Fig. 3). Also, when DPPC liposomes were exposed to higher magnetic fields than 12 T, they markedly grew. These large changes should result in an out-of-plain orientation, i.e., undulation of a membrane. The undulation structure of a membrane may be similar to the ripple structure, because when DPPC liposomes were cooled from 45 °C down to 30 °C under 12 T, an H-NMR pattern of the undulation phase was very similar to its ripple phase.^ The total energy of a liposome comprising the curvature-elastic and magnetic energies should determine the liposome growth from radius r^to r with the association of n hposomes under a magnetic field. Using the Helfrich theory for the magnetodeformation of a spherical bilayer liposome of radius r^, in which the domains in the bilayer have a local radius of curvature Po, we can get the condition for the magnetofusion and magnetodivision may occur[4]: 6{l-n)^r,(n"'-n)/p,^0

(2)

This condition is illustrated for a given Po in Fig. 4. The shading region shows magnetofusion (n >1) and magnetodivision (w 6.8xlO-' >3.1xlO-^ >4.5xl0-^ propylene glycol 4x10-' 0.6 5x10-' 2x10-' 9x10-' glycerol 0.6 6x10' 3x10-' 9x10-' 4x10-' 4. CONCLUDING REMARKS In the Cjg ,EOn systems having long EO chain, micelles are dissociated upon addition of propanol and propylene glycol, as is observed in relatively short-chain CjjEOg system. As a result, the cloud points increase. On the other hand, micelles grow upon addition of glycerol in the C,g iEOio7 system similarly to C,2E0g system, while micelles do not change in C,g.iEO„ (n=19.2, 30.1, and 50.8) systems. Therefore, the cloud point decreases only in C,g ,EOjo7 system because of the micellar growth, but the cloud points in C,8,E0„ (/2=19.2, 30.1, and 50.8) systems are unchanged with glycerol content. Namely, the cloud points increase because of the dissociation of micelles upon addition of propanol and propylene glycol, and this fact is independent on the EO-chain length. On the other hand, the cloud point decreases upon addition of glycerol because of the micellar growth in relatively short EO-chain C,g.iEO,o7 system, but the cloud point does not change in C,g ,EO„ systems having a very long EO chain (>19.2) because of no structural change in micelles. Concerning the correlation between cloud point and micellar size, therefore, we can conclude that the cloud point increases when micelles are dissociated and the cloud point decreases when micellar size increases. REFERENCES 1. K. Shigeta, U. Olsson, H. Kunieda, submitted 2. K. Aramaki, U. Olsson, Y. Yamaguchi, H. Kunieda, Langmuir, 15 (1999) 6226 3. P. Stilbs, Prog. Nucl. Magn. Reson. Spectrosc. 19 (1987) 1 4. A. Nakajima, Bull. Chem. Soc. Jpn.,50 (1977) 2473 5. D. Quemada, Rhol Acta, 16 (1977) 82 6. A. van Blanderen, J. Peetermans, G. Maret, J. K. G. Dhont, J. Chem. Phys., 96 (1992) 4591

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) (C) 2001 Elsevier Science B. V. All rights reserved.

97

Critical surface charge density for counter-ion binding in mixed micelles of ionic with non-ionic surfactant M.Manabe. H.Kawamura, H Katsu-ura, and M.Shiomi Niihama National College of Technology, Niihama, 792-8580, Japan It was found that in the mixed micelles of ionic with non-ionic surfactant, there exists a critical mole fraction Xim* (=0.103) of ionic surfactant below which the counter-ion of ionic surfactant is completely released, without any counter-ion binding. The fact implies that in the phase diagram of mixed micellar solution, the micellar region can be separated into the traditional region and a novel region in which the ionization degree of mixed micelles is unity. As for the mixed micelle at Xim*, the amount of charge (hexavalent aggregate) and the aggregation number were evaluated based on the conductivity of micellar solution. INTRODUCTION Colloid electrolytes in water release some amount of counter-ions. The degree of ionization has been considered to be a function of surface charge density The value of degree lies around 0.3 for the micelles of most ionic surfactants [1], and when a non-ionic amphiphile is solubilized in the ionic micelles, the more counter-ions are dissociated with increasing amount of the additive [2] Another evidence is that for polyelectrolytes in a simple linear form, they behave as a strong electrolytes when the distance between nearest neighbor ionizable groups is farther than a critical distance, as developed by Manning [3]. These facts suggests that in general, colloid electrolytes must have a critical surface charge density below which the counter-ions are dissociated at all. Then we have attempted to confirm the existence of such critical surface charge density in the mixed micelles of ionic with non-ionic surfactant by conductometry For the analysis of conductivity, a distinctive quantity, differential conductivity, was applied [4]. EXPERIMENTAL Respective ionic and non-ionic surfactants are used: synthesized sodium dodecylsulfate (SDS) [5] and purchased hexaoxyethylene glycol mono-dodecyl ether (RE) (Nikko Chemicals Co.,Ltd.). The aqueous solution of RE (concentration: CJ was prepared as a solvent which was used for preparing a stock solution of SDS. Small amounts of the SDS solution was consecutively added in a given amount of the non-ionic surfactant solution

98 which was kept in a conductivity cell (cell constantO 5474 cm') immersed in a water bath controlled at 25.0-1-1/100 X . After each addition, the conductivity measurements were made on a conductivity meter (HP: 4284A). RESULTS AND DISCUSSION At all C^'s studied, the specific conductivity (K) increases monotonically with an increase in the SDS concentration (CJ , where the increasing tendency in the presence of RE was more complex compared to in water. For the detail analysis of the increasing tendency, a differential conductivity was adopted, defined as the increment of K between a pair of nearest neighbor data : dic/dC, = (K.-K,)/(C,.-C,,) The dependence of dic/dC, on the square root (SQR) of C, is illustrated in Figs. 1 and 2. In water, dic/dC, decreases linearly to a break point at which the value of C is taken to be the critical micelle concentration, CMC, and then it drops in a narrow C, region to a low constant dK/dC, value. When C, is lower than CMC,,. (CMC of RE in water, 0 09mM [6]), dK/dC, decreases in the similar manner as in water, where the curve starts deviating from the straight line at lower C, than CMC,., (CMC of SDS in water), and break becomes moderate The curve reflects the CMC decrease of SDS in the presence of RE. The same tendency of differential conductivity curve was observed in the SDS solution containing a small amount of long chain alkanols[4]. Just above CMC^,,, a maximum appears at a low C, (Fig.l). When SDS is added in a micellar solution of RE, a definite maximum is observed as seen in Fig.2 which has some characteristics. The value of dK/dC, at maximum denoted by (dic/dCJ* is the highest just above CMC^., and then decreases with C„. It is noticed that (dK/dCJ* is higher than dK/dC, of SDS solution below C M C , The fact suggests the formation of 90

ou

i

I 80

^60 c o

^

^

"

!

X

:

^

^40 c/)

Cj60

u -a

13

50 0

2

4

6

8

10

12

14

0

1 2

3

4

5

6

100SQR(Q)/S(y(m)l/1^ H g l I^lationbetv^endK/dGsandGs. fig 1. Relation betv^eendK/dCs and Q . -CrpOmmol/l^ D 00995 A 0 6

0 1.5 • 5.07 A 19.999 ': 9.997 - CrF=()niid/kg

99 polyvalent aggregates. In addition, it should be emphasized that extrapolated value of dK/dC, to C,->0 at each C^ in Fig.2 is close to each other and the value is regarded to be 50 which corresponds to the equivalent conductivity of Na ion at limiting dilution. The coincidence at 50 and the increase for dK/dC, gives a following model of mixed micelle. On the addition of a small amount of SDS in a micellar solution of RE, the complete amount of surfactant ion (DS) is accommodated in the non-ionic micelles in which the electric charge becomes greater with increasing C„ whereas Na ion is freely dissolved in the bulk water. The complete accommodation was confirmed from the result that the dic/dC, values for homologous sodium alkylsulfates is coincident with each other at given C^ and C, below the maximum point, no data being shown here. On the basis of the model, the decrease of dK/dC, above the maximum can be attributed to the counter-ion binding. Namely, for the mixed micelles, the highest charge density is accomplished at the maximum which gives the critical composition i.e., the critical surface charge density below which the counter-ion is completely ionized. Then, the SDS concentration at the maximum, denoted by C,*, is plotted against C^, in Fig 3 h is obvious that the relation is linear: the least mean squares method analysis provides the slope denoted by q (= 0.1154 ) and the intercept (0.0089). The very small intercept can be taken to be zero and represents that C,* is proportional to C„. By ignoring the concentrations of both SDS and RE dissolved in monomerical state, the critical mole fraction of DS in the mixed micelle, X,^*, can be approximated as X,^* = C,*/(C,*+CJ. As a result, X,^* can be calculated as X,^*=q/(l+q)=0.103 since C,* = q C^ This value of X.^,* is significant. If the effective cross sectional area of each head group, DS and RE, can be assigned the critical surface charge density can be estimated. In addition, when the values of X,^* in some other systems will be collected in future, it can be confirmed whether the critical surface charge density is common or not in general colloid electrolytes The amount of charge, Z, of the critical ionic aggregates is estimated in the following manner. (dic/dCJ* is plotted against SQR(C,*) and SQR(C,) as illustrated in Fig.4. Each curve has a maximum. In the concentration region above the maximum in Fig.4, each curve 2.5

0

5

10

15

Cn/(inniol/kg) Fig. 3. Relation between Cs* unci Cn.

20

0

5 10 15 IOOSQR(Cii,Cs*) / SQR(mol/kg)

Mg. 4. Dependence or(dK/dCs)* on Cn and Cs*. • 'SQRcCn) DSQR(Cs*)

100 can be regarded to be linear and the linear regressive analysis provides the relations. (dk/dCJ* = -1.274 x 100SQR(CJ + 85.59, (dk/dCJ* = -3.736 x 100SQR(CJ + 85.63 (1) It is apparent that the intercepts are in good agreement with each other Both Hnear relations can be considered to have the same physical meaning: the dependence of differential conductivity on the concentration of the critical ionic aggregates Along this explanation, the intercept denoted by (dK/dCJ*" indicates the equivalent conductivity of the critical ionic aggregates at limiting dilution. If the Stokes' law is applied to the critical ionic aggregates with the charge amount (Z e), the radius R, in the aqueous solvent with its viscosity r| , the ionic mobility U, is expressed and also the ionic mobility U, of SD ion with the radius r is done as U, = Z e / (67rnR) ; U, = e/(67rrir) (2) After all, the ratio is obtained. U/U, = Z/(R/r). (3) Provided that DS ion and the critical ionic aggregate are spherical and the volumes of respective species, monomerical DS ion, and micellized DS ion and RE are identical with each other, the relation can be derived. (R/r)'-^ = Z+N (4), where N stands for the aggregation number of RE in the aggregates From Eqs.(3) and (4) and taking X,^*^ =Z/(Z+N) into account, Z can be calculated as

z = (uyu,)^^Vx,,*'^

(5)

On numerical calculation for Z, Uc/U, can be evaluated form the equivalent conductivity of respective ionic species, DS and the critical ionic aggregate, where the conductivity is evaluated by subtracting the conductivity of Na+ ion (50 1) from respective intercepts obtained in Fig.4 for the aggregate, and in Fig. 1 for SDS in water UyU, = (85.6-50.1)/(73.2-50.1)= 1.54 (6) Finally Z is calculated by Eq.(5) as 5.94 yielding N as 51 7 which seems to be reasonable. REFERENCES 1. Y. Moroi, Micelles, Prenum, New York, 1992,p.62. 2. M.Manabe, H.Kawamura, S.Kondo, M.Kojioma, and S.Tokunaga, Langmuir 6 (1990) 1596. 3. G.S.Manning, J.Phys.Chem., 79(1975)262. 4. M.Manabe, H.Kawamura, A.Yamashita, and S Tokunaga, J Colloid Interface Sci, 115 (1987)147. 5 M.Manabe, S.Kikuchi, YNakano, YKikuchi, S Tokunaga, M Koda, Memoirs of the Niihama Technical College (Science and Engeneering), 19(1983)50. 6. PBehcer, Nonionic Surfactants, Ed by M.J.Schickic, Dekker, New York, 1967, p 483

Studies in Surface Science and Catalysis 132 Y. Ivvasawa, N. Oyama and H. Kunieda (Editors) c 2001 Elsevier Science B.V. All rights reserved.

101

Dispersibility of Surfactant-free OAV Emulsions and Tlieir Stability Design: A Present Scope from Hydrocarbons to Some Oleate Esters. K. Kamogawa^•^ H. Akatsuka^ M. Matsumoto', T. Sakai^ T. Kobayashi^ H. Sakai^''^ and M. Abe^''^ ^Elem.&Sec. Ed. Bureau, Ministry of Education, Science, Sports and Culture, Kasumigaseki3-2-2, Chiyoda, Tokyo, 100-0013, Japan ''Institute of Colloid and Interface Sci., Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo, 162, Japan. ^Science University of Tokyo, 2641, Yamazaki, Noda, Chiba, 278-8510, Japan This paper presents recent development in surfactant-free emulsion (SFE) chemistry on the dispersibility and the stability for growth. Appropriate selection of the hydrophobic oil and the mixing control with the second oils realized fine dispersibility and stability for long period up to 1 year. The SFE droplets reveal prototype behavior of emulsion, which has been shielded by the amphiphilic groups. 1. INTRODUCTION Emulsion technology has been developed on the basis of surfactants and other amphiphilic substances. While they are quite useful, another needs arise today at organic-recycling or energetic consumption in the recovery.

Surfactant-free 0/W

emulsion (SFE) is, if possible, one promising solution for these needs, allowing variety of hydrophobicity design of oil phase. The oils concerned here are completely hydrophobicor slightly polar oils with HLB vs. y / 97 for n-alkanes n= 8,10,12,14 and 16fromrightto left.

Figures. < d o > vs. y Irj for alkyl oleate. CHjCB), decyKD), oleyl(0),glycerol(A) and acid(#).

30min, before discrete growth to M-class. At other temperatures, the peak positions unchanged except for a transition as shown in Fig.3. The initial dispersibility can be evaluated with the average diameter < d o>. As often referred for emulsions, the droplet size was analyzed as aftinctionof the interfacial tension(y) normalized to viscosity ( 7 ), y I rj in mPas-s/mN-m' [4]. Figure 4 reveals high correlation between < d 0> and y / rj for n-alkane oils. kXy I rj = 20-100. < d o> decreases with y I rjso that the droplet evolution above M-class in n-hexane and cyclohexane SFE is ascribable to the low viscosity. The linearity suggests that nm-scale droplets may be generated at / / 7 ~* 1. Expected oils are alkyl oleate or glycerol trioleate giving y / 7 = 1 ^ 5 . lOxlO'r CO

E CO _3 "O

2

% a

I "5 3

o

20 40 60 80 100120140 160180

Time /min

Figure 6. vs. time. Oleic acid(#), CH3(H) and glycerol(A) esters.

2

3

4

5

6

7

Time / day

Figure?. vs. time. CH3(•), decyl(n), oleyl(O) ,gIyceroI(A) esters.

104 Figure 8. log[ A < d(t) > / A t] plot against the oil

100

viscosity. CH3 ( • X d e c y U D ) , oleyl(O) and glycerol(A) esters.

As shown in Fig.5, however, their < d o > reached only at 60nm. Althou^ it seems to be a disruption 10

20 ~30 40 50 ©0 ^i^t ^^^ viscous droplets, < d o >

Viscosity /mPa • s

is certainly

regulated by the viscosity.

2.2 Two Growth Modes and Their Control The growth of SFE can be analyzed with the rate, A < d ( t ) > / At.

In the case of

oleic esters (or n-hexadecane-added tetralin), < d ( t ) > showed bipbasic increase, at the scale of few hrs and several days respectively, as seen Fig3.(6) and (7). Therefore, two modes can be distinguished in growth, as fast and slow ones. Fast mode was often found for oils soluble in water slightly. The growth presented linear rise of < d(t) ^ > with time in accord with the LSW theory as shown in Fig.6. This mode is assignable to the Ostwald ripening. Shrinkage of smaller droplet with the growth of larger droplets, an indication of the Ostwald ripening, was found for oleic acid. Stabilization of benzene- and tetralin droplets by n-nexadecane mixing [2] allows us to protect the Ostwald ripening with 2"^ oil. Slow mode rate was analyzed for oleic acid esters, in which [ A < d ( t ) > / A t

]

significantly decreased with an increase in oil viscosity in a semi-log3rithmic manner, as shown in Fig.?. This relationship does not arise from the collision-controlled ftision but from an activation energy factor, because diffusional motion is almost invariant for these dilute SFE dispersions. This indicates that the slow coalescence can be controlled dynamically with the oil phase viscosity. REFERENCES 1 .K.Kamogawa, T.Sakai, N.Momozawa, M.Shimazaki, M.Enomura, H.Sakai and M.Abe,

J. Jpn. Oil. Chem. Soc.,47( 1998 ), 159.

2.K.Kamogawa, M.Matsumoto, T.Kobayashi, T.Sakai, H.Sakai and M.Abe, .,Langmuir, 15(1999), 1913. 3.T.Sakai,.K.Kamogawa, N,Momozawa, H.Sakai and M.Abe, under submission. 4..K.Kamoga\va and M. Abe, in Encyclopedia in Emulsion Technology, Mercei Dekker Inc.NY in press.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) c^ 2001 Elsevier Science B.V. All rights reserved.

105

Solidification of Liquid Hydrocarbons with the Aid of Carboxylate Hiroshi Sakaguchi National Institute of Materials and Chemical Research, Higashil-I, Tsukuba 305-8565, Japan It was shown that, with the aid of water and very small amounts of alkyl chains of surfactants, almost all liquid hydrocarbons were easily solidified at room temperature. l.INTRODUCTION 1.1. Importance of the solidification of liquid hydrocarbons 20th century has been the period of petrochemistry. Because liquid or gaseous hydrocarbons are used as reactants, chemical reactions can be controlled easily and much amounts of high quality products have been produced. This is the essentially different point of petrochemistry compared with coal chemistry. However, at the same time, very large scale explosion or leakage accidents have increased greatly. Much care should be paid during transport, handling and storage[l]. If all hydrocarbons can be kept in solid state at room temperature, and can be returned back to the original liquid or gas state at any time we want, it will be very useful, not only for practical chemical industry or for the benefit of environment, but also on the pure scientific point of view. 1.2.Importance of van der Waals forces among alkyl chains in water Depended on intermolecular van der Waals forces[2], all hydrocarbons (and all kinds of molecules) originally have properties to gather together to make themselves solididified state. However, depended on thermal energy, which is the function of temperature, hydrocarbon molecules have properties to move around freely and randomly. As the consequence, actual pure hydrocarbons exist in a state of solid, liquid or gas, depended on temperature. 2.EXPERIMENTALS 99-100% pure sodium carboxylate, 99-100% pure hydrocarbon, and ultra-pure water(standard molar ratio 1:10-1000:1000) were put into a 20ml test tube, and heated (to 60-95°C) until sodium carboxylate was melted and

106 dissolved completely in water or in hydrocarbon. At this point, two liquid phases were coexisting. Then the liquids were mixed completely for several minutes by using vortex-mixer, and the tube was stood still at room temperature. After some time, from a few minutes to several days depended on sample to sample, self assembling occurred and a white gigantic solidified aggregate, practically including all the existing surfactant and hydrocarbon molecules, was separated from pure water. Self-assembled aggregate was analyzed by DSC, TGA, photo-microscopy, FT-IR, elemental analysis, ICP emission spectroscopy, and so on. 3.RESULTS Figure 1 shows a typical example of self-assembled solidified aggregates of sodium tetradecanoate and n-paraffins(molar ratio of 1:50) in pure water(molar ratio 1000). These aggregates were very hard and stable at room temperature, and could be picked up by fingers.

Fig. 1. Self-assembled solidified aggregates of sodium tetradecanoate and n-paraffins (molar ratio 1:50) in pure water (molar ratio 1000). From left to right; n-pentane, n-hexane and n-heptane. As sodium carboxylates, n-alkyl chain length of 12(dodecanoate) to 22 (docosanoate) were used. And as hydrocarbons, all liquid n-paraffins (from n-pentane to n-octadecane), branched parafrins(ex. 2,2,4-trimethylpentane), olefins(ex. 1-decene), and aromatic hydrocarbons (benzene, toluene, xylenes, ethylbenzene, cumene) were tested. In all the combinations of these carboxylates and hydrocarbons, and in wide ranges of molar ratios(l:l to

107

1:400-800), self-assembling always occurred, solidified aggregates were obtained, and separated from pure water. And so, in maximum cases, more than 99 weight per cent of one aggregate was composed of pure hydrocarbon, and the remaining less than 1% was composed of carboxylate. However, when molar ratio of hydrocarbon became over the limit, solidified aggregate was not produced, and two liquid phases, hydrocarbon and water, remained. Of course, in the absence of water, such self-assembling and solidification phenomenon did not occur at all. Mixture of hydrocarbon and carboxylate separated easily, mixture of caboxylate and water became stable emulsified liquid, and mixture of water and hydrocarbon separated immediately. DSC analysis showed that, in the aggregate, hydrocarbon was kept liquid state at room temperature. In case of n-heptane and sodium pentadecanoate aggregate, for example, during cooling process of DSC measurement, quantitative phase transition peak from liquid to crystal of pure n-heptane was obtained at -93°C. And so, solidified aggregate was only an apparent one. Intrinsically, the aggregate was liquid, but it could be treated like solid. By DSC measurement, it became clear that water content in each aggregate was very small and practically negligible. In water, separated from self-assembled aggregate, ICP analysis revealed that only SOppm of Na was contained. This meant that almost all carboxylate was in the aggregate. By TGA analysis, each white aggregate was usually stable at room temperature, and was decomposed around at melting point of the sodium carboxylate included. And so, at higher than the decomposition temperature, pure hydrocarbon could be easily recovered. The aggregate was really liquid, only apparently solid. However, after some adequate heat and cool treatment, the aggregate became real co-crystal of carboxylate and hydrocarbon [3]. 4.DISCUSSION This self-assembling and solidification phenomenon can be explained by intermolecular interaction, van der Waals attraction force, among alkyl chains of carboxylate and hydrocarbons. Water plays decisive role for alkyl chains attract each other, gather together and finally construct themselves to solidlike aggregate. Without water, as thermal movement of each short alkyl chain hydrocarbon is much stronger than mutual van der Waals attraction, each molecule easily go away from surrounding alkyl chains. Beside, carboxylate plays also decisive role. Carboxylate plays like anchor to catch and fasten hydrocarbons tightly in water. However, once hydrocarbons are caught and gather together, as hydrocarbons intrinsically have ability to attract each other, they can attract each other and stabilize themselves. And

108

so, only small amounts of carboxylates are necessary compared hydrocarbons. Figure 2 shows a schematic model to explain this phenomenon. H20 H20 H20 H20 H20 H20 H20 H20

H20 H20 H2O

H2O

H20 H20 H20 H20 H20 H20 H20 H20

H20

H20

^•S^.^^VX-V/

L

H20 H20 H20 H20 H20 H20 H20 H20

^

with

H20 H20 H20 H20 H20 H20 H20 H20

H20 H2O

H2O

H2O

H20 H20

H20

H20 (

H20 H20

H2O H2O H2O H2O H2O H2O H2O

Fig. 2. Self-assembling and solidification scheme. REFERENCES 1. Eberhard Weise(Volume editor), Ullmann's Encyclopedia of Industrial Chemistry, Volume B8, (1995) 497. 2. Paul C. Hiemenz and Raj Rajagopalan(eds.), Principles of Colloid and Surface Chemistry, 3rd ed.. Marcel Dekker(1997) 462. 3. H. Sakaguchi, R. Tzoneva, T. Yoshimura, and K Itoh, Proceeding on the IWCPB-HMF'99, (2000)379.

Studies in Surface Science and Catalysis 132 Y. iwasawa, N. Oyama and H. Kunieda (Editors) o 2001 Elsevier Science B.V. All rights reserved.

109

Methodology for predicting approximate shape and size distribution of micelles M. Kinoshita and Y. Sugai Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, JAPAN We propose a methodology for predicting the ^jproximate shape and size distribution of micelles with all-atom potentials. A themiodynamic theory is combined with the Monte Carlo simulated annealing technique and the reference interaction site model theory. Though the methodology can be applied to realistic models of surfectant and solvent molecules with current computational capabilities, it is illustrated for simplified models as a preliminary step. 1. INTRODUCTION Theoretical prediction of the shape and size distribution of micelles formed by aggregation of surfactant molecules in solvent is one of the most challenging problems. Molecular Dynamics (MD) and Monte Carlo (MC) simulations treating surfactant molecules and surrounding solvent molecules simultaneously have been performed with all-atom potentials. Some of them use realistic models of surfactants and solvents [1-3], but they suffer fix)m extremely heavy computational load: only a single, pre-assembled aggregate can be simulated for a very short period ( ~ 0 . Ins), and the final structure relies heavily on the initial structure chosen. Even with simplified models for surfactants and solvents [4-7], analysis on the equilibrium px)perties of the system is not an easy task, mainly because the number of solvent molecules to be treated is extremely large. A problem of the simulations is that they are able to sample only a limited region of the configurational phase space. The number of degrees of fieedom involved in the simulations is substantially reduced if the solvent molecules are omitted. This can be justified by accounting for solvent effects using the reference interaction site model (RISM) theory, an elaborate statistical-mechanical theory for molecular fluids. We propose a metiiodology in \\iiich a thermodynamic theory [8] is combined witii the MC simulated annealing technique [9-10] and tiie RISM tiieory. The RISM equations are solved using a robust and very efficient algorithm [11]. As a preliminary step of our research, the methodology is illustrated for simplified models of surfactant and solvent molecules. 2. MODEL The solvent molecule is a spherical particle V, and the surfactant molecule is a chain comprising two

110 types of atoms: a solvophilic atom A and a solvophobic atom B. The V-V, V-A, and B-B interactions are Lennard-Jones (U) potentials, and the V-B, A-A, and A-B interactions are repulsive parts of the LJ potentials. Rigid, linear surfactant molecules, AB, AABB, and ABBB, are treated with L/^L^^=Lf^= 0.20nm {LpQ is the distance between the centers of P and Q\ £'w=^vA^^vB'^^AA'=0-6kcal/mol, ^BB^^AB'^^kcal/mol, and crw=crvA=crvB=cTAA~10) are not spherical (they are more disc-like), and the asphericity increases as the size becomes larger. On the other hand, the micelles for AABB are nearly spherical in the size range tested. The micelles for ABBB of smaller sizes («10) are more cylindrical than the micelles for AABB. We have found that the micelles with the lowest value of ^c^ which are determined by the MC simulated annealing technique without the solvent, are almost completely spherical for all the three model surfactant molecules. Those micelles are destabilized in the solvent due to relatively high values of the solvation free energy. E^{n) possesses a minimum wiiile ^^{n) is a decreasing function of n. For AABB the minimum in E^(ri) is the most distinct with the result that E^n) also possesses a minimum as observed in Fig. 1. Thus, large micelles can be destabilized by the solvent effects as well as by the translation entropy effects. For ABBB a minimum is not present in Ej{n\ and a larger aggregate can be more stabilized by packing of the long solvophobic chains. Figure 2 shows the size distribution of micelles f„ {f„^nXJLnX„, X~NJNy\ N„ is the number of micelles of size n) at some different concentrations of surfactant molecules for AABB (A^ is the number of the surfactant molecules and A^v is that of the solvent molecules). The critical micelle concentration (cmc) is at N/Ny/-\0'\ We have found that cmc(ABBB)«cmc(AABB)«cmc(AB). The micelle size is the smallest for AABB because of the apparent minimum present in Sj(n). Slightly larger micelles can be formed for AB and much larger micelles for ABBB.

112 r

• r—r

AABB

AABB

o AA

AA

/

-^

I' 1'

0.4 ,

^ A A A A A A A

o

apaDO

DD

DD

N/Nv=5.0X10-*

/ \

N/Nv=1.0X10-' -

/ /\ \ /

D D D ° °

0.2

II]

-8

A

I1'.

II]

6

N/Nv=1.0X10-«

\-

-4

[I]

•

i \1

o

i

\\

ooooooo^ 10

20

4

8

12

nH Fig. 1. S^nX ^(n), and Sj(n) for AABB.

Fig. 2. Size distribution for AABB.

5. CONCLUDING REMARKS Although the model systems for wdiich our methodology is illustrated are simple, the results provide some useful information. First, the solvent effects are substantially large and must fully be incorporated. The micelle shape is variable depending on the surfactant molecule and the micelle size. The cmc decreases largely with increasing solvophobicity of the surfactant molecule. The average size of the micelles does not always become larger as the solvophobicity increases. We are extending our study to more realistic models of the surfactant and solvent molecules. REFERENCES 1. D. Brown and J. H. R. Clarice, J. Phys. Chem. 92 (1988) 2881. 2. J. C. SheUey, M. Sprik, and M. Klein, Langmuir 9 (1993) 916. 3. J. Bocker, J. Brickmann, and P. Bopp, J. Phys. Chem. 98 (1994) 712. 4. B. Smit, et al., Langmuir 9 (1993) 9. 5. S. Karabomi, et al.. Science 266 (1994) 254. 6. D. R. Rector, R van Swol, and J. R. Hendereon, Molec. Phys. 82 (1994) 1009. 7. B. J. Palmer and J. Liu, Langmuir 12 (19%) 6015. 8. A. Ben-Shaul and W. M. Gelbart, J. Phys. Chem. 86 (1982) 316. 9. S. Kiriq)atrick, C. D. Gelatt, Jr., and M. P Vecchi, Science 220 (1983) 671. 10. M. Kinoshita, Y. Okamoto, and R Hirata, J. Am. Chem. Soc. 120 (1998) 1855. 11. M. Kinoshita and R Hirata, J. Chem. Phys. 104 (1996) 8807. 12. M. Kinoshita and Y. Sugai, Chem. Phys. Lett., 313 (1999) 685. 13. J.C»HC1 in the aqueous solution. Because the activities of DC»H+ and CI" were depressed each other, it is expected that premicelles including both ions are formed in the solution. We consider that other monovalent cationic species except DC»H+ are able to response the DC^H+ electrode as follows -3.0

-2.5

-2.0

-1.5

-1.0

log [DC-HCI],. log [NaCI] / mol dm^

mDC-H"*" + (m - l)Cr

Fig. 1. Relationship between electrode potential and E)C»HC1 or NaCl concentration: The equilibrium constant {K) of the above reaction (1) dibucaine cation, (2) chloride ion is expressed as (DC*HC1), (3) chloride ion (NaCl). -(DC-H)^Cl(,.,/

(1)

115 K = [(DC*H)^Cl(^.,)^]/[DC.H*r[Cr]^'"-^^

(2)

obtained from the electrode is given by The apparent concentration of DC • H+ ([DC • H"^\^^) iapp>' [DC-H^],pp = [DC-H*] + A [ ( D C - H ) , a ( , . , ) n

(3)

where X is the response coefficient of the electrode for (DC»H)^C1(^. ^"^ ion. Total concentration of dibucaine ([IX: • HClJt) can be written using the concentration of DC-H+ [DC*HC11^ = [DC*H^] + m[(DC*H)^Cl(^.,)^]

(4)

From Eqs. (3) and (4), we obtain [DC-HCl], - [DC-H^],pp = (m -A)[(DC-H)^C1(,. ,)^]

(5)

Alternatively, using CI" ion concentration, [DC* HClj^ is written as [DC*HCl]t - [CI] = (m .1)[(DC*H)^C1(^.,)^]

(6)

By combining Eqs. (5) and (6), ([DC*HCl]t - [DCH^],pp)/([DC•HCIJj - [CI]) = (m - ^)/(m - 1)

(7)

The A value can be determined experimentally if we can know the m value. Considering ionic equilibrium given by Eq. (1), the following two equations can be obtained. ([DC*HCl]t - [DC•H-'])/[DC•H^]'" = mA:[Cr]^'" ''^

(8)

and ([DC*HC1], - [Cr])/[Cl-]^'"-^> = (m -1)A:[DC«H^]'"

(9)

where [DC • H"*"] is not measurable directly and obtainable from the equation [DC*H^] = [DC-H^],pp - A/(m -l)([DC-HCI]t - [Cl'l)

(10)

Right hand side of Eq. (10) can be determined with the m value by the EMF measurements. Both activity depressions were analyzed by the above equations with several m values. We found that the m value of 3 held on the Eqs. (8) and (9). The results are shown in Fig. 2,

10

20

(Crf X I0*/mol^dm*

20

40

60

[DC«H*f X I0*/mol^clm'"

Fig. 2. Validity of pre-micelle formation with m = 3: (A) plot of Eq. (8), (B) plot of Eq. (9).

116 respectively: good linear relationship in both figures with m = 3 was obtained. The values of ^ and A were found to be 6.21 (± 0.18) x 10* (moH kg^) and 0.50 ± 0.14 at 298.15 K, respectively. This fact indicates that at the concentration below the CMC, DC^HCl forms a trimer with two chloride ions. The pre-micelle formation of dibucaine may be attributable to the n electron interaction of an aromatic ring with a butyl chain in the molecule. 3.2. Formation and growth of DC*HC1 micelle at concentrations above the CMC We next performed the static and dynamic light scattering (SLS and DLS) measurements on various concentrations of aqueous E>C»HC1 solutions in the absence and presence of added sodium chloride (NaCl). The static scattered light intensity greatly increased at concentrations above the CMC. The aggregation numbers of the anesthetic micelle were evaluated from Debye plot of the intensity data. The value of 15 was obtained for DC»HC1 micelles in water and it is consistent with literature ones [3,4]. Since E)C»HC1 form trimers at concentrations below the CMC, five dibucaine trimers associate cooperatively and form the micelle at concentrations above the CMC. Furthermore, the CMC decreased and the aggregation number increased by the addition of NaCl. Micellar properties of E)C»HC1 in water and NaCl solutions were sununarized in Table 1 together with the average diameters of DC^HCl micelle, which were obtained by DLS measurements. Although the average diameter increased with increasing NaCl concentration, the variation of the aggregation number with NaCl concentration seemed not to be threedimensional as seen in surfactants with a straight hydrophobic chain. This fact suggests that the E>C»HC1 micelle grows one-dimensional direction like small rod-like micelle in the aqueous solution by addition of NaCl. The micellar growth of DC*HC1 in solutions of high ionic strength may result from the stacking of an aromatic ring in the molecule. Table 1 Micellar properties of DC*HC1 in water and NaCl solutions NaCl cone. (molkg-»)

0

0.10

0.15 a)

0.30

0.40

0.50

0.60

79.4

51.0

40.9

28.2

22.5

20.8

18.3

Aggregation number

15

29

34

40

45

53

59

Average diameter (nm)

1.9

2.8

3.3

4.1

4.8

5.2

6.1

CMC(mmolkg-0

*) physiological saline concentration. REFERENCES 1. T. Eckert, E. Kilb and H. Hoffman, Arch. Pharm., 297 (1964) 31. 2. R. Jaenicke, Kolloid. Z., 212 (1966) 36. 3. E. H. Johnson and D. B. Ludlum, Biochem. Pharmacol., 18 (1969) 2675. 4. D.Attwood and P Fletcher, J. Pharm. Pharmacol., 38 (1986) 494. 5. H. Matsuki and S. Kaneshina, Hyomen (in Japanese), 37 (1999) 20. 6. H. Matsuki, M. Yamanaka, S. Kaneshina, H. Kamaya and I. Ueda, Colloids Surfaces B: Biointerfaces, 11 (1998) 87. 7. H.Satake, T. Miyata and S. Kaneshina, Bull. Chem. Soc. Jpn., 64 (1991) 3029.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyamaand H. Kunieda (Editors) c: 2001 Elsevier Science B.V. All rights reserved.

^1/

Ionic partition to zwitterionic micelles Kenji Iso and Tetsuo Okada Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan Capillary electrophoresis has been used to measure the ^-potential of zwitterionic micelles in various electrolytes. Even for intrinsically neutral zwitterionic micelles, detectable ^-potential is induced by the imbalance between anionic and cationic partition. Its magnitude and sign are determined by the natures of ions (dominantly anionic ones) and the polarity of surfactant molecules. However, the former is a principal factor governing the
100

0

2

4

6

8

10

12

14

aClOGl wt% 0.002

Fig 1: phase diagram of a-CioGi • solution temperature on heating o recrystallisation on cooling A 1(|) to liquid-liquid transition

0.004 0.006 decanol wt%

0.008

0.01

Fig 2a Influence of traces of SDeS on the phase diagram of a-CioGi (2.6 wt%) 2b Influence of decanol on the phase behaviour of 0.93 wt% a-CioGi which contains 0.07 % SDeS, Symbols see fig 1

151 The extension of this miscibility gap decreases strongly when small amounts of sodium decylsulfate are present (fig 2a, cf decyl p-D-glucopyranoside [8]) and increases when decanol (fig 2b) or octanol are added. Only milky dispersions are obtained when the ternary systems of a-CioGi / octanol or decanol / water are heated above the solution temperature of the surfactant. No single phase regions are formed in the investigated temperature region up to 100 °C. On the other side a-CioGi and SDeS form low viscous isotropic micellar solutions above the solution temperature of the surfactant mixtures. The phase behaviour becomes much more interesting when traces of SDeS are present in the a-CioGi / decanol / water system. At 30 °C 0.9 wt% a-CioGi and 10'^ wt% SDeS (that means 1.1 % in a-CioGi) form a crystalline dispersion. The phase volume intersection (fig 3a) shows that the crystals are transformed to coloured phases when decanol is added. With 0.15 - 0.25 % decanol an iridescent phase grows from the bottom of the tube below a turbid isotropic phase. This region disappears by about 0.30 wt% decanol and a blue iridescent single phase region is obtained. At 0.73 wt% the system becomes turbid and colourless. Higher amounts of decanol remain undissolved and form a decanol rich L2 phase which separates as concentrated upper phase above the iridescent region. Blue iridescence is found above green, red and colourless which indicates sedimentation effects. The phase diagram intersection fig. 3b elucidates the transformation from ternary system with decanol to the swollen lamellar phase in dependence of the SDeS concentration. Below 0.6 % SDeS only milky dispersions are found. With concentrations between 0.6 ~ 0.9 % SDeS in a-CjoGi a turbid phase which display blue to green colours is observed. Above 1% a blue iridescent single phase region appears . The iridescent disappears when the amount of SDeS is increased above 1.7 %, however a bluish scattering remains. It should be emphasized that the weight ratio of ionic surfactant to decyl a-D-glucopyranoside which is necessary for the swollen lamellar phase is in the order of 0.010 - 0.017. This means that it is sufficient that only about one of 100 surfactant molecules in the lamellar structure is an ionic one. Increasing the fraction of the sulfate decreases the optical birefringence. This is an indication for a continuous transformation from a planar lamellar structure to a system with charged vesicles.

0,5 Ti

0.5 4-

1

0.2

0.4 0.6 0.8 decanol wt%

1.2

b

B

C

^

• • • • < !

0.5

1

1.5

2

2.5

(mass ratio SDeS / a^^^G^riOO

Fig 3) phase volume intersection, T= 30 °C a) 0.92 wt% a-CioGi, 0.0092 wt% SDeS b) 0.92 wt% a-CjoGi, 0.48 wt% decanol t = slightly turbid, R,G,B = red, green or blue iridescence, m = milky dispersion, c = coloured milky dispersion , b = colourless region with flow birefringence and bluish scattering.

152 Strongly iridescent phases can be obtained with pure decyl a-D-glucopyranoside or with mixtures of decyl a/p-D-glucopyranosides and octanol or decanol. The system aCioGi/decanol/SDeS in a weight ratio of 97/66/0.97 displays linear swelling on dilution for a total volume fraction > 0.009. This corresponds to a maximum interlamellar distance of 248 nm with a Bragg Peak at 660 nm. The bilayer thickness is 2.30 nm. Some more examples are presented in table 1. The appearance of two 5r ?"

(a)1 1

0

>\-|

0.06

'^S^^v^

1—i_i

11J

rk-

CL 0 . 0 2

n-hex

~" ^

10^

n-hexane 1

r—r-^

rT)

it

1

1

'

•

(b)

j

= 0.04 n-heptane

(0

rr

'S 0.02

0 0.06

0

Fig. 1. wo dependence of the scattering curves of w/o AOT microemulsions (water/AOT//i-hexane, (a); n-heptane. (b); n-octane, (c)) occluding achymotiypsin (2.4x10-5 M).

50

100 150 r(A)

200

^^' 2. Distance distribution functions p(r) of the scattering curves of AOT microemulsions shown ^" ^ - 1./i-hexane, (a);/i-heptane, (b); n-octane, ^«>- V«"°^^ ^^"^« ^^^ ^ ^" ^^- ^•

>^max. Whereupon, the change of the p(r) occurs in the different manner for each system, especially at low water contents. The tailing of the p{r) function to a long distance direction can be seen at wo = 4 for the n-hexane system, at wo = 4 - 8 for the n-heptane system, and wo = 4 - 12 for the n-octane system, respectively. As explained previously [3], the tailing of the p(r) function suggests the presence of a certain amount of oUgomeric AOT microemulsion particles at tiie low water contents. Thus, Pig. 2 shows that the lengthening of the hydrocarbon chain of the apolar solvent extends the transient region from the oligomeric phase to the monomeric phase. Figs. 3(a) and

168

10 20 30 40 [HgOMAOT] (M/M)

50

Pig. 3. wo dependence of the J7g (a) and p{r)max (Jb) of w/o AOT microemulsions occluding achymotiypsin (2.4xl0-^ M).

0.1

0.2 [El (mM)

Fig. 4. Protein concentration dependence ofp(r) function (a) andp(r)inax (b). In (a), water/AOT/nhexane at wo = 20.

3flb) show the WQ dependence of the Rg andp(r)max, respectively. The relation between the WQ andp(r)niax values shows a good linearity for all systems. Whereas, with the lengthening of the hydrocarbon chain the wo vs. Rg relation becomes to deviate from a simple linearity and to separate into three different regions with different slopes. The slope above wo = 16 becomes smaller with the lengthening of the hydrocarbon chain. These results depending on the hydrocarbon chain length are essentially the same as those observed in the w/o AOT microemvdsion systems without proteins [5]. In Fig. 4 the protein concentration dependence of the pir) function and p(r)max shows that the occlusion of the proteins tends to decrease the microemulsion radius, which is more clearly seen with increasing water content or with shortening the hydrocarbon chain length. This would result from the attractive electrostatic interaction between the polar head of AOT and the basic residues of the protein surface.

REFERENCES 1. R. Hilhorst, In Structure and Reactivity in Reversed Micelles; Pileni, M. P. (ed.), Elsevier, Amsterdam, (1989) 323. 2. R. H. Pain (ed.). Mechanisms of Protein Folding, IRL Press, New York, 1994. 3. M. Hirai, et al., J. Chem. Soc. Faraday Trans., 91 (1995) 1081; J. Phys. Chem., 99 (1995) 6652. 4. M. Hirai, et al., J. Phys. Chem. Solids, 60 (1999) 1297. 5. M. Hirai, et al., J. Phys. Chem. B, 103 (1999) 9658.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) (C) 2001 Elsevier Science B.V. All rights reserved.

169

Phase transition in Gibbs monolayers of mixed surfactants Md. Mufazzal Hossain,* Tomomichi Okano^ and Teiji Kato** * Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, Yoto 7-1-2, Utsunomiya 321-8585, Japan ^ Lion corporation, Tokyo, Japan Abstract Phase transitions in mixed monolayers of 2-hydroxyethyl laurate (2-HEL) and Na-salt of 3,6,9,12tetra oxa octacosanoic acid (TOOCNa) formed by co-adsorption fiom their mixed bulk solutions have been studied. The presence of cusp points followed by plateau regions in tiie 7c-t curves, vs4iich is accompanied by two phase coexistent state indicates afirst-orderphase transition. The domains have circular shape with internal segments whereas those of pure 2-HEL at the same temperature are of fingering pattem with uniform brightness all over the domains. With increasing thefi:actionof TOOCNa, the domains show more and more expanded behavior which favor easy fusion of tiiem. 1. INTRODUCTION In recent years, we as well as several other research groups have demonstrated the existence of first-order phase transition fiom gas or liquid expanded to condensed phase in Gibbs monolayers of highly purified amphiphiles.[l,2] Extensive research has been performed on mixed surfactant systems, since they can show superior performance as compared to single surfactant alone. When a trace of dodecanol is added to sodium dodecyl sulfate solution die interfacial properties of the aqueous solutions are markedly altered. This is attributed to an increase in packing and ordering of the monolayers at the air-water interfece due to the co-adsorption of dodecanol.[3] Shah et aL [4] proposed that when two surfactants are mixed with a molar ratio of 1:3, the properties of the surfactant systems are changed strikingly due to 2D hexagonal packing oftiiemolecules. Recently, Bain et aL [5] reportedtiiephase transition in the mixed monolayers of cationic surfactants and dodecanol at the airwater interface by sumfiiequencyspectroscopy. In this paper, we evidently report that two water soluble surfactants show a first-order phase transition and form liquid condensed (LC) domains in an appropriate mixture. We have chosen 2hydroxyethyl laurate (2-HEL) and Na-sak of 3,6,9,12-tetraoxa octacosanoic acid (TOOCNa) as amphiphiles (Fig.l).

170 2-HEL:

CH3(CH2),OCCXX:H2CH20H

/ COONa TOOCNa:

CH3(CH2)i50"

^^

^^

^O'

Fig. 1. Chemical structures of the surfactants used in this study 2. EXPERIMENTAL The material, 2-HEL was synthesized with a purity of > 99.5% and TOOCNa was obtained fix)m Lion corporation, Japan with a purity of > 99%. The solutions were prepared separately in ultra pure water of resistivity 18 M Q -cm and then mixed in appropriate volume ratio to obtain the desired molar ratio. To specify the ratio of a given mixture in the latter part of this paper, we always follow the order 2-HEL: TOOCNa. The surfece pressure-time (u-t) curves were measured in a home buik Langmuir trough of very shallow type. The experimental procedure [6] was detailed elsewhere. The surface pressure was measured by the Wilhehny metfiod and the domain morphology was characterized simultaneously by Brewster angle microscopy (BAM) [7] using 20 mW He-Ne laser as a light source. 3. RESULTS AND DISCUSSION Fig. 2 shows 7i-t adsorption kinetics of 2.0 X10'^ M aqueous solutions of both the surfactants separately and in mixed solutions v^th different concentration ratios at 15°C. This concentration is suflBcient to form condensed domains by only 2-HEL but not sufficient to do that by TOOCNa. Condensed domain

formation

in

pure

TOOCNa

monolayer is not possible even with more OHicentration solutions because these are

Fig. 2.7c-t adsorption kinetics at 15°C of 2.0 X10'^ M

above its cmc. Under the present conditions,

aqueous solution of 2-HEL (I), TOOCNa (V), and

the rate of adsorption for pure TOOCNa is

their mixtures with diffoent molar ratios of 2-

higher than that of 2-HEL but in the mixed

HELrTOOCNa; 3:1 (II), 1:1 (ffl), 2:3 (iV). The

system this rate is in between the pure

vertical arrows indicate the position of the cusp points

systems. WrAi increase in the fraction of

in the reflective curves.

TOOCNa in the mixture, the overall rate of adsorption increases indicating the co-adsorption of the surfactants. However, the 7c-t curves in the figure show the cusp points followed by plateau regions up to die ratio 2:3. For spread monolayers of some otiier amphiphiles, a true cusp point in the surface

171 pressure-area (TC-A) isothenns indicates a discontinuity in 5G/57C (G, Gibbs fiee eneigy) because 5G/57C =A. This is the characteristic of afirst-orderphase transition. Since, A decreases with time in Gibbs monolayers, a cusp point in the n-t curve also indicates afirst-orderphase transition.[l,2] hi the 7c-t curve of ratio 3:1 (curve II), the concentration of 2-HEL is only 1.5 X10'^ M which is not suflScient to form condensed domains at 1 5 t when it is used alone.[8] However, phase transition is possible in the mixed system of ratio 2:3 where the concentration of 2-HEL is only 0.8 X10'^ M. These results demonstratetiiatthe existence of phase transition in these systems are due to both of the surfactants. The critical surfece pressures {n^ necessary for the phase transition are almost Ae same except in one case where the fiction of 2-HEL isrelativelylow (curve IV). hi the latter case, tiie TC, is higher than those of the other systems. This should be due to the rapid adsorption of mainly TOOCNa molecules which cover most of the surfaces before a considerable amount of 2-HEL can accumulate to initiate condensation. However, once the concentration of 2-HEL becomes sufficient LC domain formation starts, but before this can happen the surfece pressure becomes almost close to the equilibrium value of TOOCNa. With further decrease in thefiactionof 2-HEL beyond 2:3, phase transition vanish. The in situ BAM observation for all the curves with cusp points shows condensed domains which become larger with time and finally solution surface is covered with them. Fig. 3 presents the typical shape and texture of the domains of pure 2-HEL and the mixed surfactants at 15°C. For pure 2-HEL, the domains are of fingering pattern with uniform brightness all over the domains (image A) at this temperature. The shape of tiie domains for mixed monolayers is circular with inner segments (images B-D) at and above this

Fig. 3. Shapes and textures of the domains formed

temperature. For the mbced surfactant system of

in the monolayers of 2-HEL (A) and the mixed

ratio 3:1, the most of the domains have stripe

systems of ratio 2:3 (B-D). Size: 400 X 300 pml

pattem. With increase in thefiactionof TOOCNa, the texture of the domains becomes irregular with a variety of pattem. Few examples of different defects are given in the Fig. 3 (images B-D). The fusion of tiie domains is rarely observed during the formation process of the domains in pure 2-HEL and even in mixed surfactants containing higher fiaction of 2-HEL (ratio 3:1). However, fusion becomes more and more favorable witii increase in the flection of TOOCNa. Fig. 3D presents an elliptical domain which is formed by the fusion of two circular domains. This type of fusion is rather a common phenomenon during the monolayer formation in the mixed system of ratio 2:3.

172

All theseresultscan be explained considering formation of the mixed monolayers. Withtfieratio 3:1 of the surfactants, the monolayers is dominated by tiie 2-HEL, but considerable extent of TCXXnSIa molecules is included intotiiedomains. For other cases, the extent of 2-HEL molecules is comparatively small. Since, TOOCNa contains sixteen carbon chain, it is expected to have higher line tension if it is introduced into the domains. This high line tension causes circular shape domains although the pure 2-HEL show fingering pattem.[8,9] At 15°C, the 2-HEL molecules remain almost normal to tiie surface, wiiich causes uniform brightness in these monolayers.[8] Nevertheless, the TOOCNa molecules containing longer carbon chain as well as larger hydrophilic group should be tilted. Thus, overall balance among these molecules should cause such complex pattern in the monolayers. With decrease in thefractionof 2-HEL, the monolayers have a tendency to show more irregular textured domains. This is a clear evidence in favor of the formation of domains by both of the surfactants because for pure surfactantsregularpattern is ahvays observed. The irregular pattern most probably due totfieuneven distribution of the components in the domains. We must take consideration of the repulsive forces e.g. electrostatic, dipolar, hydration etc. of the long hydrophilic head groups of TOOCNa molecules. W^ith decrease in the fraction of 2-HEL, tiie tendency of incorporation of TOOCNa molecules into the domains increases. When the concentration of 2-HEL is sufficiently low to initiate condensed domain formation, phase transition does not occur. 4. CONCLUSIONS We provide evidence for the first-order phase transition in mixed monolayers of two water soluble amphiphiles, 2-HEL and TOOCNa. It is clearfix)mthe BAM images that the formed domains contain both of the component, although the exact composition is still unknown. The circular domain formation in these monolayers is a direct evidence for the effect of line tension on domain shape. The irregular textured domain formation may be attributed to an uneven distribution of the surfactants at the diflFerent part of the domains. REFERENCES l.D. Vollhardt, V. Melzer, J. Phys. Chem. B 101 (1997) 3370. 2.M. M. Hossain, M. Yoshida, T Kato, Langmuir 16 (2000) 3345. 3. B. D. Casson, C. D. Bain, J. Phys. Chem. B102 (1998) 7434. 4. A. Patist, S. Devi, D. O. Shah, Langmuir 15 (1999) 7403. 5. B. D. Casson, C. D. Bain, J. Phys. Chem. B 103 (1999) 4678. 6. M. M. Hossain, M. Yoshida, K. Iimura,N. Suzuki, T Kato, ColloidSmf.A 171 (2000) 105 7. S. Henon, J. Meunier, Rev. Sci. Imtnrn. 62 (1991) 936. 8. M. M. Hossain, T. Kato, Langmuir 2000 (in press) 9. S. Siegel, D. Vollharxit, Thin Solid Films 284/285 (19%) 424.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) c 2001 Elsevier Science B.V. All rights reserved.

173

Mesoscopic structures of J aggregates of organic dyes at a solid/liquid interface and in solution: spectroscopic and microscopic studies Hiroshi Yao,* Sadaaki Yamamoto,** Noboni Kitamura*' and Keisaku Kimura" ^ Faculty of Science, Himeji Institute of Technology, Hyogo 678-1297, Japan ^ Material Science Laboratory, Mitsui Chemicals, Inc., Chiba 299-0265, Japan "^ Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan Supramolecular structures in J aggregate systems are characterized. J aggregates of a pseudoisocyanine dye (PIC) at a mica/solution interface were in situ observed by tapping-mode atomic force microscopy (AFM). The single aggregates possessed a three-dimensional disk-like island structure in a mesoscopic scale. The island size ranged -400-600 nm long, -100 nm wide, and -3-6 nm high. Morphological differences can be observed between the J aggregates at a solid/liquid interface and those in bulk solution. Mesoscopic string structures of 5,5'-dichloro-3,3'-disulfopropyl thiacyanine (TC) J aggregates were detected in an aqueous solution for the first time by both fluorescence microscopy and microspectroscopy. The length of the J string was several tens of \im while the width was very narrow. 1. INTRODUCTION Extensive research has been directed toward a better understanding of supramolecular aggregate systems and their interesting optical and electronic properties (!]. 7 aggregates are specific dye supramolecular assemblies characterized by a narrow and intense absorption band that shows a bathochromic shift compared to the relevant monomer band. Since the aggregate structure reflects highly on its spectroscopic properties, detailed investigations of the structures and/or morphologies of the single aggregates are of primary importance. Thus, we examined morphologies and optical properties of different types of mesoscopic J aggregate systems: J aggregates at a solid/liquid interface and in a solution phase. 2. EXPERIMENTAL l,r-Diethyl-2,2'-cyanine chloride (pseudoisocyanine; abbreviated as PIC) and 5,5'-dichloro-3,3'-disulfopropyl thiacyanine (abbreviated as TC) were purchased from Nippon Kankoh-Shikiso Kenkyusho Co., and used as received. Conventional absorption and fluorescence measurements were carried out on a Hitachi U-3300 spectrophotometer and an F-4500 spectrofluorometer, respectively.

174

In order to investigate J aggregate formation at a mica/water interface, cationic PIC dye was used. A sample for spectroscopic measurements was prepared by placing an aliquot of an aqueous PIC solution between mica and hydrophobic glass plate. A TC dye was used for examining the structure of J aggregates produced in a solution phase. A solution sample was prepared by dissolving TC sodium salt in an aqueous NaCl solution (5.0 mM). AFM images were recorded on a Nanoscope Ilia (Digital Instruments) operating at a tapping-mode in a liquid phase. Triangular Si3N4 microcantilevers (Nanoprobe; NP-S, Digital Instruments) possessing a spring constant of 0.58 Nm*' were used. Fluorescence microscope images were obtained by using a CCD camera (Hitachi, Remote Eye) set on an optical microscope (Nikon, Optiphoto-2). Fluorescence microspectroscopy was conducted by using a polychromator-multichannel photodetector set (Hamamatsu Photonics, PMA-11) equipped on the microscope. A monochromatic beam (454.5 nm) was used as the excitation sources. A sharp-cut filter (Y-47) was mounted in front of the CCD camera and photodetector set. 3. RESULTS AND DISCUSSION 3.1.

Mesoscopic island structures of PIC single J aggregates at a mica/water interface Figure 1 shows an optical path length dependence of the absorption spectrum of an aqueous PIC solution (2.0 mM). The spectrum showed a sharp and intense J band (580 nm). It is worth noting that no J band can be observed when using a hydrophobic glass cell. Moreover, the figure indicates clearly that the J band is independent of the path length while the bulk monomer (525 nm) or dimer band (480 nm) increases with increasing the path length. The results indicate that J aggregate formation is concluded to be confined to the vicinity of the mica/solution interface.

400

500 600 Wavelength / nm

Fig. 1. Optical path length dependence of the absorption spectrum measured for an aqueous PIC solution (2.0 mM) between mica and hydrophobic glass plate.

2 Mm

Fig. 2. AFM top-view image of the PIC J aggregates at a mica/solution interface (|PIC| = 0.2 mM). Arrows show the periodic orientation of negative holes on mica surface.

175

Thus, atomic force microscopy (AFM) was conducted to examine the microstructures of the J aggregates at the interface. Figure 2 shows AFM image at [PIC] = 0.2 mM. Since the mica surface was unchanged and atomically flat until the J band appeared (< 0.1 mM), the observed mesoscopic leaf-like islands were considered to be the J aggregates. The size of these islands ranged -400-600 nm long, -100 nm wide, and -3-6 nm high. Interestingly, our AFM image revealed that the J aggregates have a three-dimensional disk-like structure but not a two-dimensional monolayer structure. In addition, morphological changes of the islands were observed with changing the PIC concentration: The number density of the J islands increased with increasing PIC concentration, and then, they coalesced into larger domains. In contrast, the height of the islands was independent of the PIC concentration [3]. The constant height of the islands would be determined by the balance between the adsorption/aggregation and dissolution energies. Furthermore, the long axis of the islands are anisotropically oriented relative to the alignment of the negative holes on mica surface formed by dissociating K"^ ions, which was shown as white arrows (three directions) in Figure 2. The results suggest the existence of epitaxial interaction between PIC molecules and the lattice of a mica substrate. The highly probable epitaxial interaction is the one that the positively charged N atoms of the dye are placed at the negative holes on mica [4,5]. jisland _ _ - --_ According to this epitaxial interaction, there are two possible alignments of / \ ^ the dye molecules in the islands: the L Q Cl C Q O C . long axes of the dye are either parallel ^ ' ^/ r^crc" o :, s^ o o or 60** relative to the long axes of the islands. In terms of energy, however, the dye molecules may grow so that

O

the long axis of dye molecules is parallel to the long axis of the islands as shown in Figure 3, which shows an energetically stable brick-stonework alignment of dye molecules.

cziizj

negative holes on the mica surlace

PIC molecules

Fig. 3. Schematic model of the alignment of PIC molecules in a J aggregate island.

3.2. Mesoscopic string structures of TC single J aggregates in solution On the other hand, structural and/or morphological differences are expected between the J aggregates at a solid/liquid interface and those produced in bulk solution. We demonstrate that fluorescence microscopy and microspectroscopy enable a direct observation of single J aggregates in solution. Here, we examined the microstructures of 5,5'-dichloro-3,3'-disulfopropyl thiacyanine (TC) J aggregates in an aqueous solution. Figure 4 shows a fluorescence microscope image at [TC] = 0.05 mM, above which the J band appears, and mesoscopic string structures were clearly observed. Since a characteristic fluorescence image was not detected below this concentration.

176

the strings distributed in solution were considered to be 7 aggregates of TC. To the best of our knowledge, this is the first observation of mesoscopic J aggregates in a solution phase. The length of the string was several tens of \km while the width was very narrow; sub-^m. This string structure is probably due to anisotropic interactions between TC molecules in solution (i.e., quasi-one-dimensional stacking interactions), different from that of PIC J aggregates observed at a mica/water interface. It is noteworthy that a single string is likely to bend in an arc form, suggesting that the mesoscopic J aggregate is flexible and polycrystalline-like. Figure 5 shows fluorescence spectra observed for a single string of J aggregates and at the periphery of the string. The excitation beam diameter was -10 jim, and the measurements were conducted at various position in the string. However, the spectral shape did not change with the observation position in the string. Since the spectrum was quite similar to that measured in bulk solution, the strings detected in Figure 4 were concluded to be TC 7 aggregates. It is worth noting that fluorescence was scarcely observed at the outer periphery of the string, indicating that TC in an aqueous solution produces exclusively mesoscopic-size J aggregates.

i 200 >,0 c «

periphery of the string

S 100

30f,im

Fig. 4. Fluorescence microscope image of the TC J aggregates in an aqueous solution ([TC] = 0.05 mM). The strings correspond to the TC J aggregates.

u

^m^^^

400

450

600 500 550 Wavelength / nm

650

Fig. 5. Fluorescence spectra observed for a single string of TC J aggregates and at the periphery of the string.

REFERENCES 1. P. W. Bohn, Annu. Rev. Phys. Chem., 44 (1993) 37. 2. H. Schmidt, J. Vac. Sci. Technol. A, 8 (1990) 388. 3. H. Yao, S. Sugiyama, R. Kawabata, H. Ikeda, O. Matsuoka, S. Yamamoto and N. Kitamura, J. Phys. Chem. B, 103 (1999) 4452. 4. V. Czikkely, H. D. Forsertling and H. Kuhn, Chem. Phys. Lett., 6 (1970) 11. 5. S. S. Ono, H. Yao, O. Matsuoka, R. Kawabata, N. Kitamura and S. Yamamoto, J. Phys. Chem. B, 103 (1999) 6909.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) i£' 2001 Elsevier Science B.V. All rights reserved.

177

Energy of Breaking of Aqueous GEMINI Surfactant Film Tadahiko Kidokoro and Junichi Igarashi Department of Chemistry, Faculty of Science, Tokai University 1117 Kita-Kaname, Hiratsuka-shi, Kanagawa-ken 259-1292, Japan l.Introduction A number of methods have been proposed for measuring the surface tension of a liquid. Single liquid film is considered to be a very simple colloid system, and is useful for elucidating various colloidal and interfacial phenomena. Interest has been shown by many investigators, particularly upon the effect of aqueous ionic surfactant for its drainage of the film. However, there are few such reports on ionic Gemini surfactant films. Surface active substance usually forms a stable adsorption film in the surface or interface of liquids. As the typical methods for studying the mechanical behavior of such a surface film, equilibrium method of measuring surface free energy( Op), namely the surface tension measurement and dynamic film detachment method of measuring surface film detachment followed by its breaking( a p) are listed. In the case of pure liquid, a p= a p is assumed to hold, since pure liquid rarely produces a stable foam. However, in the case of aqueous surfactant solution, excess energy corresponding to a F ~ cr p = a pp is confirmed to detach the aqueous surfactant thin film from its aqueous surface. Thus, the value of o pp in such a case is considered as the measure of the film stability. In the present study, a reliable measurement of this energy of surface film detachment is attempted. For this purpose, we adopted the frame method that enabled the process of dynamic film detachment to occur in a well-defined condition. The measurement of 0 pp is carried out for the aqueous solutions of Gemini type surfactant, and the stability of aqueous thin film is discussed by taking into account of the structure of Gemini molecule. For this purpose, frame method is original and especially suited for the measurement of surface tension in the present case. Here, we attempt to establish an empirical equation available for the calculation of a p, since there are no empirical equations of Harkins and Brown, and Harkins and Jordan in drop weight method and ring method, respectively. The difference of the interfacial tension of several mNm' is obtained in ionic surfactant and nonionic surfactant surface, which exists qualitative values.

178 Here, the Gemini style surfactants that were synthesized in recent years were investigated sufficiently the surface properties especially for the properties mentioned above. 2.£xperimental Z.l.Materials The sample of Gemini surfactant used here is disodium N-N - bis [(2-carboxyethyl) lauroylamide] ethylene diamine corresponding to monomer, made by KANEBO, Ltd., Cosmetics Lab. Product. The water used was distilled from a solution prepared by dissolving potassium permanganate and sodium hydroxide in ion-exchanged water, using borosilicate glass equipment immediately before each measurement. Pure liquids (water, cyclohexane, toluene, and chlorobenzene) were obtained by twice simple distillation. These solutions were freshly prepared just before the use. 2.2.Apparatus The cell was submerged in a thermostated water bath of 303.15±0.2K, and the whole apparatus was set in a chamber of 303.15 ±0.2K for about 15 hours before the measurement. Air room (gas phase) is filled with nitrogen gas. 2.3.Method In the present measurement, the glass frame used for frame method was shown in Fig.l- i . A microscopic cover glass with a perimeter of 21=8.030cm was used as a plate, to which a thin glass rod carrying the hook was attached as shown Fig.lii. The frame used was made of glass rod of 0.51mm in diameter and 2L=8.856cm in width as shown in Fig.li. = 0 . 5 1 Kill! Pure water and the aqueous solution, whose surface tension is considered to 21-8.()3()cni be constant at a constant temperature is put in vessel, which is slowly raised Fig.l-ii Fig.1- i until the surface just touches the low end Glass f r a n i e s ( i ) and P l a t e ( i i ) used in t h i s study. of the plate. Gemini solution used was put in the vessel, o p and o p were measured after about 15 hours aging cither by Wilhelmy method or frame method. The solutions were gradually ra sed. le frame was vertically withdrawn at the rate 0.75~2.5mmsec"^ from the solution by electric motor. The vessel was

179 contained about 300ml of the solution. The surface tension of both the plate and frame are converted to the electric signal by strain gauge UR-2GR of MINEVEA Co., Ltd. and is put into the recorder connected. The plate and frame were cleaned before each measurement by immersing it in chromic acid mixture for about 8 hours , followed by rinsing with water. 3.Result and Discussion The frame method of measuring downward pull of liquid is considered as the more idealized method of measuring the force of film detachment. Since we have no equations applicable for the frame method, as it exists in the case of drop weight JQQ method of Harkins and Brown, and ring 79J [• 79.6 ^ method of Harkins and Jordan, we 79.4 attempted first to establish an empirical ' e 79J r z equation applicable for the calculation I 79.0 •' 3 of a p, by using pure liquids such as water, cyclohexane, chlorobenzene and 78.6 ^ 78.4 [ toluene. 782 j^ In the case of film extension rate of 78.0 — 0.75"^2.5mmsec'^ range, a straight line 0.4 0.6 0.0 V7(n»n-»ec")'' relation was obtained as shown in Fig.2 between film tension (P/2L) and inverse Fig.2 Surface tension as a function of V'^ of film extension rate V"^ for pure liquid. From the extrapolated value of (P/2L) to V^=0 as expressed by (P/2L)oo, and a p, A a is obtained as shown equation(l). (P/2L)oo-ap=Aa (1) Figure 3 shows plots of A a in each pure liquid against (P/2L)c», showing a straight line of equation (2). A a =0.0899(P/2L)«,-0.6018 (2) In the present study, surface detachment energy a p measured by the frame method is defined as Eq.(3), aF=(P/2L)oo-A a (3) From Eqs. (2) and (3), Eq. (4) is obtained, a F=0.9101(P/2L)oo+0.6018 (4) Here mNm'^ is used as the unit of surface tension. As examples, the detachment process of the film in the frame method at regular rate of film expansion is shown in Fig.4. The pattern

180 showed maximum B, and shows a linear rise in according to the change in expansion rating of the film in the case of Gemini systems A.B.C and D. increased with downward speed.

As shown in Fig.4 surface cut energy

Similar variation was also observed with an increase in

concentration.

D

B

b 30


gel-H^ lamellar L.C.-* disk like micelle, while in a region of ^0-70wt% the state changes at 15'X:gel-I-^ hexagonal L.C., and above 70% the hexagonal L.C. changes to a micellar solution at 100-130X:. In the case of Ca(UD)2-water system (Fig.3B), aggregation state changes as coagel^ gel-* lamellar L.C.-* disk-like micelle, and a region of 50-80wt% a transition expected to be a disk-like micelle-* micellar solution transition was observed. Above ]50V thermal polymerization occurred gradually. 3.2 7 -Ray-Irradiation Polymerization in Various States In the 7 -ray-irradiation polymerization of KUD-water and Ca(UD)z-water systems, polymerization proceeded rapidly and saturated after 3-^ hours. The polymerizability of KUD was highest in the coagel state at water contents of 70'-80wt% and the maximum conversion reached to 60 % as shown in Figure ^A. On the contrary, the polymerizability of Ca(UD)2 was highest in the coagel at water contents of ]0---20wt%, and the maximum conversion was ca. 23 % (Fig. ^B). In both cases, the polymerizability decreased in the order of coagel, gel-1, gel-B and lamellar liquid crystal. It can be concluded that the regular arrangement of the monomer molecules together with mobility of terminal vinyl groups is an important factor for the polymerization, although details of the results obtained in this work are not consistent with the results of sodium and zinc 10-undecenoates in aqueous systems[2]. REFERENCES 1. M.Kodama and S.Seki, J.Colloid Interface Sci., 117(1987)^85. 2. Y.Shibasaki and K.Fukuda, Colloids and Surfaces, 67(1992)195. 3. A.Fujimori, H.Saitoh and Y.Shibasaki, J.Therm.Anal.Calori.,57(1999)631. ^. A.Fujimori, H.Saitoh and Y.Shibasaki, J.Polym.Sci.,A:Polym.Chem.,37( 1999)3845.

Studies in Surface Science and Catalysis 132 Y. Iwasawa, N. Oyama and H. Kunieda (Editors) c 2001 Elsevier Science B.V. All rights reserved.

185

Effects of Shear Flow on the Structure of the Lamellar Phase Formed in Nonionic Surfactant-Water System K. Minewaki^, T. Kato^ and M. Imai^ ^Department of Chemistry, Tokyo Metropolitan University, Minamiohsawa, Hachioji, Tokyo, 192-0397, Japan ^Department of Physics, Ochanomizu University, Ohtsuka, Bunkyo-ku, Tokyo 112-0012, Japan Small-angle neutron scattering has been measured on the lamellar phase formed in a nonionic surfactant (Ci6E7)-water system under shear flow at shear rates in the range 10~'^-10^ s""^ From the dependence of the peak position and the peak intensity on the shear rate it has been suggested that the lamellar domain is disrupted into small fragments at shear rates about 0.1^1 s~^ and that the original microstructure is reconstructed at higher shear rates. 1. INTRODUCTION In recent years, the effects of shear flow on the structure of the lamellar phase formed by nonionic surfactants have been investigated by using microscopy[1], viscometry[l], small-angle neutron scattering (SANS) [1-3], light scattering[l], and NMR[1,4] and attention has been paid to the formation of multilayered vesicles by shear flow and the orientation of the sample for structural analyses. In a previous paper, we studied the effects of shear flow on the structure of the lamellar phase in Ci6H33(OCH2CH2)70H (abbreviated as Ci6E7)-water system by using SANS in the range of shear rate 7 = 10"^10^ s~^ which is much lower than that of other studies reported so far. It has been shown that significant changes in the peak position and the peak intensity were observed at 7 c^ 0.1 s~^[5]. In these measurements, however, we used the neutron beam only along the gradient direction by which the perpendicular and transverse orientations are observed (orientation of the layer normal along the vorticity, flow, and velocity gradient directions are referred to as perpendicular, transverse, and parallel, respectively). In this study, measurements have been made by using a neutron beam along both gradient (radial) and flow (tangential) directions alternatively at each shear rate. In addition, effects of the

186

0.5

1.0

1.5

2.0 0.5

q/nm-

1.0

1.5

2.0

q / nm~

Fig. 1. Scattering intensities for the vorticity direction at 328 K (a) and 343 K (b) integrated over a sector of ±10° at different shear rates. The results at 343 K have been already reported [5].

0.5

1.0

1.5

q I nm-^

2.0 0.5

1.0

1.5

2.0

q I nvar^

Fig. 2. Scattering intensities for the flow (a) and vorticity (b) directions at 328 K integrated over a sector of ±10° at different shear rates (different run from that of Figure 1(a)).

shear history have been examined. 2. E X P E R I M E N T S Measurements of SANS were carried out at the instrument SANS-U of Institute for SoHd State Physics of University of Tokyo in JRR-3M at Tokai with a Couette shear cell[6]. All the measurements were made for the sample containing 55 wt% of CieEy at 328 K and 343 K. 3. R E S U L T S A N D D I S C U S S I O N Figures l a and l b show the scattering intensities for the vorticity direction at 328 K

187

«

vorticity direction —o— gradient direction - -o—

1.4 1.3 1.2

p^ 500 IS 400 [

0 0.0010.01 0.1

1

10 100

Fig. 3. Shear rate dependence of the peak position (a) and the peak intensity (b) of the first reflection for the vorticity direction at 328 K an 343 K.

vorticity direction —o— gradient direction -o--0-'-