Surfaces, Interfaces, and Colloids: Principles and Applications, Second Edition. Drew Myers Copyright 1999 John Wiley & Sons, Inc. ISBNs: 0-471-33060-4 (Hardback); 0-471-23499-0 (Electronic) SURFACES, INTERFACES, AND COLLOIDS SURFACES, INTERFACES, AND COLLOIDS Principles and Applications SECOND EDITION Drew Myers New York • Chichester • Weinheim • Brisbane • Singapore • Toronto Designations used by companies to distinguish their products are often claimed as trademarks. In all inatances where John Wiley & Sons, Inc., is aware of a claim, the product names appear in initial capital or ALL CAPITAL LETTERS.
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This work is dedicated to: Christine Betty Jimmy Linda CONTENTS Preface to the Second Edition xvii Preface to the First Edition xix 1 Surfaces and Colloids: The Twilight Zone 1 1.1 Introduction: The World of Neglected Dimensions 1 1.2 An Historical Prospective 5 1.3 A View to the Future 6 Problems 7 2 Surfaces and Interfaces: General Concepts 8 2.1 The Nature of Interfaces 8 2.2 Surface Free Energy 10 2.1 The Work of Cohesion and Adhesion 13 2.2 Standard Reference States 18 2.3 The Molecular Nature of the Interfacial Region 18 Problems 20 3 Surface Activity and Surfactant Structures 21 3.1 Basic Structural Requirements for Surface Activity 21 3.2 Surfactant Structures and Sources 23 3.1 The Classification of Surfactants 24 3.2 Building Blocks for Surfactant Molecules 25 3.3 Surfactant Solubilizing Groups 29 3.4 Common Surfactant Hydrophobic Groups 30 3.3 The Economic Importance of Surfactants 34 3.4 Surfactants in the Environment 36 3.1 Biodegradation of Surfactants 36 3.2 Rules for Biodegradation 37 Problems 38 4 Attractive Forces 40 4.1 Chemical and Physical Interactions 40 4.2 The Importance of Long-Range Physical Forces 41 vii viii CONTENTS 4.3 Classification of Physical Forces 42 4.1 Coulombic or Electrostatic Interactions 43 4.2 Other Interactions Involving Ions 45 4.4 van der Waals Forces 55 4.1 Dipole–Dipole Interactions 55 4.2 Angle-Averaged Dipolar Interactions 57 4.3 Dipole-Induced Dipole Interactions 57 4.4 The London–van der Waals (Dispersion) Force 58 4.5 Total van der Waals Interactions between Polar Molecules 62 4.6 Effects of a Nonvacuum Medium 64 4.5 Interactions between Surfaces and Particles 66 4.1 Surface Interactions in Nonvacuum Media 67 4.2 Dipole, Induced Dipole, and Hydrogen Bonding (Acid–Base) Interactions at Interfaces 68 4.6 Lifshitz Theory: A Continuum Approach 69 4.1 Some Shortcomings of the Hamaker and Lifshitz Theories 72 4.2 Hard Sphere Diameter Effects 72 4.7 Hydrodynamic Flow Effects in Interfacial Interactions 74 Problems 77 5 Electrostatic Forces and the Electrical Double Layer 79 5.1 Sources of Interfacial Charge 79 5.1 Differential Ion Solubility 81 5.2 Direct Ionization of Surface Groups 81 5.3 Substitution of Surface Ions 82 5.4 Specific-Ion Adsorption 82 5.2 Electrostatic Theory: Coulomb’s Law 83 5.1 Boltzman’s Distribution and the Electrical Double Layer 84 5.2 Double-Layer Thickness: The Debye Length 85 5.3 Specific-Ion Adsorption and the Stern Layer 88 5.2 Moving-Boundary Electrophoresis 93 5.3 Gel (Zone) Electrophoresis 93 CONTENTS ix 5.4 Some Practical Comments on Electrokinetic Characteristics 94 Problems 96 6 Capillarity 97 6.1 Fluid Properties and Dynamics 97 6.3 Capillary Driving Forces in Liquid–Fluid Systems 101 6.1 Solid–Liquid–Fluid Systems: the Effect of Contact Angle 103 6.2 Capillary Flow and Spreading Processes 104 6.3 Geometric Considerations in Capillary Flow 107 6.4 Measurement of Capillary Driving Forces 109 6.5 Complications to Capillary Flow Analysis 112 6.6 Rates and Patterns of Capillary Flow 117 6.4 Some Practical Capillary Systems 118 6.1 Wetting in Woven Fibers and Papers 118 6.2 Waterproofing or Repellency Control 121 6.3 Capillary Action in Detergency Processes 122 Problems 123 7 Solid Surfaces 125 7.1 Surface Mobility in Solids 125 7.2 ‘‘History’’ and the Characteristics of Solid Surfaces 129 7.3 Solid Surface Free Energy vs Surface Tension 130 7.4 The Formation of Solid Surfaces 132 7.3 Amorphous Solid Surfaces 135 Problems 138 8 Liquid–Fluid Interfaces 140 8.1 The Nature of a Liquid Surface: Surface Tension 140 8.2 Temperature Effects on Surface Tension 143 x CONTENTS 8.3 The Effect of Surface Curvature 144 8.4 Dynamic Surface Tension 145 8.2 Surface Tensions of Solutions 147 8.1 Surfactants and the Reduction of Surface Tension 150 8.2 Effects of Phase Densities 151 8.3 Surfactant Adsorption and Gibbs Monolayers 151 8.1 Efficiency, Effectiveness, and Surfactant Structure 152 8.4 Insoluble Monomolecular Films 158 8.5 The Physical States of Monolayer Films 162 8.4 Some Factors Affecting the Type of Film Formed 167 8.5 Mixed-Film Formation 170 8.6 Surface Films of Polymers and Proteins 171 8.7 Monolayer Films at Liquid–Liquid Interfaces and on Nonaqueous Liquids 172 8.8 Deposited Monolayers and Multilayer Films 173 8.6 A Final Comment 174 Problems 174 9 Adsorption 179 9.1 The Gibbs Surface Excess 180 9.2 The Gibbs Adsorption Equation 183 9.2 Adsorption at the Solid–Vapor Interface 186 9.1 Energetic Considerations: Physical Adsorption versus Chemisorption 187 9.2 Chemisorption and Heterogeneous Catalysis 190 9.3 Catalytic Promoters and Poisons 193 9.3 Solid–Vapor Adsorption Isotherms 193 9.1 Classification of Adsorption Isotherms 194 9.2 The Langmuir Isotherm 196 9.3 The Freundlich Adsorption Isotherm 197 CONTENTS xi 9.4 The Brunauer–Emmett–Teller (BET) Isotherm 198 9.5 Surface Areas from the BET Isotherm 198 9.4 Adsorption at Solid–Liquid Interfaces 199 9.5 The Adsorption Model 200 9.6 Quantification of Surfactant Adsorption 202 9.1 Adsorption Isotherms in Solid–Liquid Systems 202 9.2 Adsorption and Modification of the Solid–Liquid Interface 204 9.3 Adsorption and Nature of the Adsorbent Surface 204 9.4 Environmental Effects on Adsorption 208 9.5 Effects of Adsorption on the Nature of the Solid Surface 210 Problems 211 10 Colloids and Colloidal Stability 214 10.1 The Importance of Colloids and Colloidal Phenomena 214 10.2 Colloids: A Working Definition 215 10.3 Some Points of Nomenclature 218 10.3 Mechanisms of Colloid Formation 219 10.1 Comminution or Dispersion Methods 219 10.4 The ‘‘Roots’’ of Colloidal Behavior 222 10.5 Ground Rules for Colloidal Stability 223 10.1 A Problem of Semantics 225 10.2 Mechanisms of Stabilization 226 10.3 A Review of Basic Intermolecular Forces 226 10.4 Fundamental Interparticle Forces 228 10.5 Attractive Interactions in Nonvacuum Media 229 10.6 Sources of Colloidal Stability 230 10.1 Charged Surfaces and the Electrical Double Layer 231 10.2 Some Complicating Factors 231 10.7 Steric or Enthalpic Stabilization 233 10.1 The Mechanism of Steric Stabilization 234 10.2 Solvent Effects in Steric Stabilization 236 10.3 Effects of Polymer Molecular Weight 237 10.4 Depletion Flocculation 238 xii CONTENTS 10.1 Kinetics of Particle Collisions: Fast Coagulation 239 10.3 Critical Coagulation Concentration 243 10.4 The Deryagin–Landau–Verwey–Overbeek (DLVO) Theory 244 10.5 Reversible Flocculation and the Secondary Minimum 247 10.9 The Complete Interaction Curve 248 Problems 248 11 Emulsions 253 11.1 Fundamental Concepts in Emulsion Science and Technology 253 11.3 Emulsions and the Liquid–Liquid Interface 255 11.1 Classification of Emulsifiers and Stabilizers 256 11.2 What Determines Emulsion Types? 258 11.4 Adsorption at Liquid–Liquid Interfaces 259 11.5 General Considerations of Emulsion Formation and Stability 261 11.6 Some Mechanistic Details of Stabilization 262 11.1 Polymeric Emulsifiers and Stabilizers 263 11.4 Surfactant Structure and Emulsion Performance 265 11.5 Liquid Crystals and Emulsion Stability 266 11.6 Mixed Surfactant Systems and Interfacial Complexes 267 11.8 The Hydrophile–Lipophile Balance (HLB) 270 11.9 Cohesive Energies and the Solubility Parameter 273 11.7 Solubility Parameters, Surfactants, and Emulsions 278 11.8 The Relationship between HLB and Solubility Parameter 281 11.9 The Geometric Approach 282 11.1 Phase Inversion Temperature (PIT) 283 11.2 Application of HLB and PIT in Emulsion Formulation 284 11.3 Some Other Factors Affecting Stability 286 CONTENTS xiii 11.1 Nomenclature for Multiple Emulsions 289 11.2 Preparation and Stability of Multiple Emulsions 289 11.3 Primary Emulsion Breakdown 291 11.4 The Surfactants and Phase Components 293 Problems 293 12 Foams 293 12.1 The Importance of Foams 295 12.3 Basic Properties of Foams 297 12.4 Foam Stability or Persistence 298 12.1 Thermodynamic Conditions for Stability 302 12.5 Practical Control of Foamability and Persistence 303 12.1 Monomeric Surfactant Stabilization 306 12.2 Polymers and Foam Stabilization 306 12.6 Foam Formation and Surfactant Structure 307 12.7 Liquid Crystals and Foam Stability 309 12.8 The Effects of Additives on Surfactant Foaming Properties 310 12.9 Foam Inhibition 312 Problems 314 13 Aerosols 317 13.1 The Importance of Aerosols 317 13.2 Colloidal Properties of Aerosols 318 13.1 Dynamics of the Aerosol Movement 319 13.2 Colloidal Interactions in Aerosols 321 13.3 Liquid Aerosols: Mists and Fogs 323 13.1 Spraying and Related Mechanisms of Mist and Fog Formation 324 13.2 Inertial Processes for Drop Formation 325 13.5 Aerosol Formation by Condensation 328 13.4 Solid Aerosols: Dust and Smoke 331 13.5 The Destruction of Aerosols 333 Problems 337 xiv CONTENTS 14 Polymers at Interfaces 339 14.1 The Solubility of Macromolecules 339 14.1 Statistics of Polymer Chain Conformations in Solution 340 14.2 Problems with Random Walks 341 14.2 Adsorption of Polymers at Interfaces 341 14.3 Polymer–Surfactant Interactions 344 14.1 Mechanisms of Polymer–Surfactant Complex Formation 346 14.2 Polymers, Surfactants, and Solubilization 354 14.3 Emulsion Polymerization 354 Problems 356 15 Association Colloids: Micelles, Vesicles, and Membranes 358 15.1 Surfactant Solubility, Krafft Temperature, and Cloud Point 359 15.2 Surfactant Liquid Crystals 362 15.1 Manifestations of Micelle Formation 366 15.2 Classic Thermodynamics of Micelle Formation 369 15.3 Free Energy of Micellization 371 15.4 Molecular Geometry and the Formation of Association Colloids 373 15.5 Some Correlations between Surfactant Structure, Environment, and Micellization 378 15.2 The Critical Micelle Concentration 380 15.3 The Effect of Additives 384 15.4 Micelle Formation in Mixed-Surfactant Systems 387 15.5 Micelle Formation in Nonaqueous Media 388 15.6 Vesicles and Bilayer Membranes 390 15.2 Polymerized Vesicles and Lipid Bilayers 392 15.1 Membrane Surfactants or Lipids 393 15.2 Membrane Dynamics 395 Problems 395 16 Solubilization, Micellar Catalysis, and Microemulsions 397 16.1 Solubilization 397 CONTENTS xv 16.1 The ‘‘Geography’’ of Solubilization 398 16.2 The Solubilization Process 400 16.3 Generalizations on Surfactant Structure and Solubilizing Power 401 16.4 Solubilization and the Nature of the Additive 402 16.5 The Effect of Temperature on Solubilization 402 16.7 The Effects of Added Electrolyte 403 16.8 Miscellaneous Factors Affecting Solubilization 404 16.2 Solubilization and Nutrition 405 16.1 Catalysis in Aqueous Solvent 407 16.2 Catalysis in Nonaqueous Solvents 409 16.1 Micelle, Microemulsion, or Macroemulsion? 410 16.2 Negative Interfacial Tensions 412 Problems 413 17 Wetting and Spreading 415 17.1 The Contact Angle 415 17.1 Contact Angle Measurement Techniques 419 17.2 Contact Angle Hysteresis 419 17.3 The Effects of Surface Roughness on Contact Angles and Wetting 420 17.5 Kinetic Aspects of Hysteresis 422 17.2 The Thermodynamics of Wetting 423 17.2 The Spreading Coefficient 425 17.3 Classification of Wetting Processes 426 17.4 Additional Useful Thermodynamic Relationships for Wetting 428 17.3 Contact Angles and Calculation of Solid Surface Energies 430 17.1 The Critical Surface Tension of Wetting 432 17.2 Some Practical Drawbacks 434 17.4 The Kinetics of Wetting 435 17.1 Factors Affecting Dynamic Wetting Phenomena 437 xvi CONTENTS 17.6 Effects of Surfactants on Wetting Processes 439 17.1 Surfactant Effects on Nonpolar Surfaces 441 17.2 Surfactants and Wetting on Polar Surfaces 442 Problems 445 18 Friction, Lubriation, and Wear 448 18.2 Friction and the Nature of the Surface 451 18.1 Metals and Metal Oxides 452 18.2 Crystals with Relatively Isotropic Structures 453 18.3 Anisotropic or Layered Crystalline Materials 453 18.