Modern Aspects of Emulsion Science Edited by Bernard P. Binks Department of Chemistry, University ofhull, UK THE ROYAL SOCIETY OF CHEMISTRY Information Services
Chapter 1 Emulsions - Recent Advances in Understanding Bernard P Binks 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Introduction Emulsion Type and the System Hydrophile-Lipophile Balance 1.2.1 Emulsions of Two Liquid Phases 1.2.2 Emulsions of Three Liquid Phases Phase Inversion Emulsion Stability 1.4.1 Creaming 1.4.2 Flocculation 1.4.3 Coalescence 1.4.4 Ostwald Ripening Gel Emulsions Forces between Oil-Water Interfaces 1.6.1 Forces between Emulsion Drops 1.6.2 Forces between a Drop and a Planar Oil-Water Interface References 1 2 2 8 10 13 13 17 26 33 38 42 42 44 48 Chapter 2 Emulsion Formation 56 Pieter Walstra and Pauline E.A. Smulders 2.1 Introduction 56 2.2 Regimes 58 2.3 Droplet Break-up 60 2.3.1 Laminar Flow 61 2.3.2 Turbulent Flow 66.2.3.3 Effect of Droplet Viscosity 69 2.3.4 Effects of Scale and Continuous Phase Viscosity 73 2.4 Roles of the Surfactant 74 2.4.1 Surfactant Properties 76 2.4.2 Effective Interfacial Tension 79 2.4.3 Effect on Droplet Deformation 83 2.4.4 Preventing Recoalescence 88 2.4.5 'Spontaneous Emulsification' 91
Vlll 2.5 Further Considerations 92 2.5.1 Effects of Volume Fraction 92 2.5.2 Emulsification Efficiency 95 2.5.3 Membrane Emulsification 97 2.6 Concluding Remarks 97 2.7 References 98 Chapter 3 Emulsion Formation by Nucleation and Growth Mechanisms 100 Brian Vincent, Zoltan Kiraly and Tim M. Obey 3.1 Introduction 100 3.2 Physical Methods 105 3.3 Chemical Methods 110 3.4 References 114 Chapter 4 Emulsion Flocculation and Creaming 115 Margaret M. Robins and David J. Hibberd 4.1 Introduction 115 4.1.1 Instability Processes 115 4.1.2 Strategies for Stability 117 4.1.3 Interaction Potential between Droplets 118 4.1.4 Flocculation Due to Polymers 120 4.2 Emulsion Creaming 122 4.2.1 Introduction and Theoretical Principles 122 4.2.2 Ultrasonic Monitoring of Creaming 124 4.2.3 Creamingof Polydisperse Emulsions without Added Polymer 128 4.2.4 Creaming of Emulsions with Low Concentrations of Non-adsorbing polymer 130 4.2.5 Creaming of Emulsions with High Concentrations of Non-adsorbing Polymer 131 4.2.6 Creamingof Emulsions with Adsorbing Polymer 133 4.3 Non-intrusive Determination of Flocculation in Emulsions 137 4.3.1 Introduction and the Principle of Ultrasonic Scattering 137 4.3.2 Ultrasonic Scattering from Unflocculated Emulsions 139 4.3.3 Ultrasonic Scattering from Emulsions during Depletion Flocculation 141 4.4 Summary 141 4.5 References 143 Chapter 5 Rheology of Emulsions - The Relationship to Structure and Stability 145 Eric Dickinson 5.1 Introduction 145 5.2 Theoretical Background 146 5.2.1 Dilute Dispersions of Spherical Particles 147
5.2.2 Concentrated Dispersions of Spherical Particles 150 5.2.3 Flocculated Emulsions 152 5.3 Experimental Investigations 157 5.3.1 Non-flocculated Emulsions 157 5.3.2 Flocculated Emulsions 163 5.4 References 171 Chapter 6 Phase Inversion and Drop Formation in Agitated Liquid-Liquid Dispersions in the Presence of Nonionic Surfactants 175 Brian W. Brooks, Howard N. Richmond and Mohamed Zerfa 6.1 Introduction 175 6.2 Basic Principles of Phase Inversion 176 6.2.1 Dissolution State of Nonionic Surfactants 177 6.2.2 Change of Phase Behaviour with Temperature 178 6.2.3 Factors Affecting Phase Inversion 179 6.3 Dynamic Inversion Maps 189 6.4 Catastrophic Inversion 191 6.5 Transitional Inversion 194 6.6 Partitioning of Surfactant 197 6.6.1 Basis of Phase Separation Model 198 6.6.2 Theory Applied to Transitional Inversion 198 6.6.3 Lumping of Distributed Surfactant Terms 200 6.7 Concluding Remarks 201 6.8 References 202 Chapter 7 Coalescence in Emulsions 205 Alexey S. Kabalnov 7.1 Introduction 205 7.2 Thermodynamic Properties of Surfactant Monolayers: Phase Behavior, Monolayer Elasticity and Interfacial Tension 206 7.2.1 Surfactant Adsorption and Micellization 207 7.2.2 Elasticity of Monolayers 207 7.2.3 Spontaneous Curvature 211 7.2.4 Implications for the Phase Behavior 214 7.2.5 Interfacial Tension 216 7.3 Experimental Trends in Macroemulsion Stability 218 7.3.1 Surfactant Nature: Oriented Wedge Trend 218 7.3.2 Bancroft's Rule 220 7.3.3 HLB Scale 221 7.3.4 'Molecular Complexes' 223 7.3.5 PIT Concept 224 7.3.6 'Optimal Surfactant Formulation' 226 7.3.7 Other Empirical Correlations 227 7.3.8 Multiple Emulsions 229 ix
X 7.3.9 Surfactant Concentration: Tight Monolayer Packing 229 7.3.10 Concentration for Formation of Black Films, C black 230 7.3.11 Stabilization by a Lamellar Phase 231 7.3.12 Effectof Volume Fractionof Disperse Phase and Droplet Size 232 7.4 Theoryof Emulsion Coalescence 232 7.4.1 Rupture of Single Films and the Emulsion Lifetime 232 7.4.2 Activation Energy: de Vries Theory 234 7.4.3 The Kabalnov-Wennerström Theory 237 7.4.4 Nucleation Pore in Multilamellar-covered Emulsion Films 247 7.5 The Kabalnov-Wennerström Theory versus Experiment 248 7.5.1 Experimental Measurements of the Activation Energy and the Pre-exponent 248 7.5.2 C 12 E 5 -n-octane-water-nacl System: Overall Trend 250 7.5.3 Winsor III Region 252 7.5.4 Winsor II Region 253 7.5.5 Pre-exponent 254 7.5.6 Surfactant Concentration 255 7.6 Summary and Outlook 256 7.7 References 257 Chapter 8 Lifetime and Destruction of Concentrated Emulsions Undergoing Coalescence 261 Benedicte Deminiere, Annie Colin, Fernando Leal Calderon and Jeröme Bibette 8.1 Introduction 261 8.2 Thin Film Metastability: Background 263 8.3 Destruction of Concentrated Emulsions Undergoing Coalescence 266 8.4 Droplet Growth in Dense Emulsions Undergoing Coalescence 268 8.5 Growth Model for Dense Emulsions 272 8.6 Determination of a^r), co 0 and a 275 8.7 Discussion 281 8.8 Conclusion 290 8.9 References 290 Chapter 9 Molecular Diffusion in Emulsions and Emulsion Mixtures 292 Jeffry G. Weers 9.1 Ostwald Ripening 292 9.1.1 The Kelvin Equation 292 9.1.2 Lifshitz-Slezov-Wagner (LSW) Theory 293 9.2 Deviations from LSW Theory 297 9.2.1 Effect ofbrownian Motion 297 9.2.2 Effect of Disperse Phase Volume Fraction 298 9.2.3 Role of Micelles in Facilitating Molecular Diffusion 299 9.3 Stabilization ofemulsions withrespectto Ostwald Ripening 303
9.3.1 Ostwald Ripening in Emulsions Containing Two Disperse Phase Components - 303 9.3.2 Effect of the Interfacial Layer in Slowing Ostwald Ripening 305 9.3.3 Other Ways of Slowing Ostwald Ripening 308 9.4 Effect of Ostwald Ripening on Initial DropletSize 308 9.5 Composition Ripening 310 9.6 Praetical Importanceof Molecular Diffusion 314 9.6.1 Ostwald Ripening in Fluorocarbon Emulsions 314 9.6.2 Ostwald Ripening in Triglyceride Emulsions with Added Ethanol 318 9.6.3 Miniemulsion Polymerization 318 9.6.4 Use of Composition Ripening to Produce Large Monodisperse Latex Particles 320 9.6.5 Stabilization of Gas Emulsions 320 9.7 References 325 XI Chapter 10 Interactions and Macroscopic Properties of Emulsions and M icroemulsions 328 Dimiter N. Petsev 10.1 Introduction 328 10.2 Pair Energy of Interaction 329 10.2.1 van der Waals Interaction Energy 330 10.2.2 Interactions Calculated by Means of Derjuagin's Approximation 331 10.2.3 Interaction Energy Contributions Due to the Interfacial Properties of the Individual Droplet-Surface Area Extension and Bending Energies 336 10.2.4 Applications of the Expressions for the Pair Interaction Energy 339 10.2.5 Accuracy of the Model Shape-Actual Geometry of Two Interacting Deformable Droplets 349 10.3 Dense Systems 351 10.3.1 Nonionic Emulsions and Microemulsions 352 10.3.2 Ionic Emulsions and Microemulsions 360 10.4 Concluding Remarks 363 10.5 References 363 Chapter 11 Gel Emulsions - Relationship between Phase Behaviour and Formation 367 Conxita Solans, Ramon Pons andhironobu Kunieda 11.1 Introduction 367 11.2 Gel Emulsions: Stractural Aspects and Properties 368 11.2.1 Structure 368 11.2.2 Stability 370
xii 11.2.3 Rheological Properties 374 11.2.4 Diffusion. 377 11.3 Gel Emulsion Formation 381 11.3.1 Phase Behaviour of Water/Polyoxyethylene Nonionic Surfactant/Oil Systems 381 11.3.2 Methods of Preparation 383 11.4 Relationship between Phase Behaviour and Spontaneous Gel Emulsion Formation 385 11.4.1 Water-in-oil (W/O) Gel Emulsions 385 11.4.2 Oil-in-water (O/W) Gel Emulsions 390 11.5 References 393 Chapter 12 Applications of Emulsions 395 Thomas Förster and Wolfgang von Rybinski 12.1 Introduction 395 12.2 Cosmetics 396 12.2.1 Spreading Properties and Viscosity 396 12.2.2 NewTypes of Emulsions 399 12.2.3 Microemulsions 401 12.2.4 Skin Penetration 404 12.3 Metal Processing 407 12.3.1 Rolling Oil Emulsions 407 12.3.2 Lubricant Emulsions 408 12.4 Textiles 409 12.4.1 Textile Fiber Preparations 409 12.4.2 Textile Finishing 410 12.5 Oilfields 411 12.6 Washing and Cleaning Processes 412 12.6.1 Detergency Mechanisms 412 12.6.2 Dry Cleaning 417 12.6.3 Microemulsion Cleaners 418 12.7 Soil Remediation 420 12.8 References 423 Subject Index 427