Colloid Science Principles, methods and applications

Colloid Science Principles, methods and applications Second Edition Edited by TERENCE COSGROVE School of Chemistry, University of Bristol, Bristol, UK WILEY A John Wiley and Sons, Ltd, Publication

Contents Preface Introduction Acknowledgements List of Contributors xv xvii xix xxi 1 An Introduction to Colloids 1 Roy Hughes 1.1 Introduction 1 1.2 Basic Definitions 5 1.2.1 Concentration 5 1.2.2 Interfacial Area 10 1.2.3 Effective Concentrations 11 1.2.4 Average Separation 12 1.3 Stability 14 1.3.1 Quiescent Systems 15 1.3.2 Sedimentation or Creaming 16 1.3.3 Shearing Flows 17 1.3.4 Other Forms of Instability 17 1.4 Colloid Frontiers 18 References 20 2 Charge in Colloidal Systems 23 David Fermin and Jason Riley 2.1 Introduction 23 2.2 The Origin of Surface Charge 24 2.2.1 Ionisation of Surface Groups 24 2.2.2 Ion Adsorption 25 2.2.3 Dissolution of Ionic Solids 25 2.2.4 Isomorphous Substitution 25 2.2.5 Potential Determining Ions 25 2.3 The Electrochemical Double Layer 26 2.3.1 The Stern-Gouy-Chapman (SGC) Model of the Double Layer 26 2.3.2 The Double Layer at the Hg/Electrolyte Interface 30 2.3.3 Specific Adsorption 34 2.3.4 Interparticle Forces 36

v/77 Contents 2.4 Electrokinetic Properties 36 2.4.1 Electrolyte Flow 36 2.4.2 Streaming Potential Measurements 37 2.4.3 Electro-osmosis 38 2.4.4 Electrophoresis 39 2.4.5 Electroacoustic Technique 42 References 42 3 Stability of Charge-stabilised Colloids 45 John Eastman 3.1 Introduction 45 3.2 The Colloidal Pair Potential 46 3.2.1 Attractive Forces 46 3.2.2 Electrostatic Repulsion 47 3.2.3 Effect of Particle Concentration 49 3.2.4 Total Potential 50 3.3 Criteria for Stability 51 3.3.1 Salt Concentration 51 3.3.2 Counter-ion Valency 52 3.3.3 Zeta Potential 54 3.3.4 Particle Size 54 3.4 Kinetics of Coagulation 55 3.4.1 Diffusion-limited Rapid Coagulation 55 3.4.2 Interaction-limited Coagulation 56 3.4.3 ExperimentalDeterminationofc.ee. 57 3.5 Conclusions 58 References 59 4 Surfactant Aggregation and Adsorption at Interfaces 61 Julian Eastoe 4.1 Introduction 61 4.2 Characteristic Features of Surfactants 61 4.3 Classification and Applications of Surfactants 62 4.3.1 Types of Surfactants 62 4.3.2 Surfactant Uses and Development 64 4.4 Adsorption of Surfactants at Interfaces 66 4.4.1 Surface Tension and Surface Activity 66 4.4.2 Surface Excess and Thermodynamics of Adsorption 67 4.4.3 Efficiency and Effectiveness of Surfactant Adsorption 71 4.5 Surfactant Solubility 73 4.5.1 The Krafft Temperature 73 4.5.2 The Cloud Point 74 4.6 Micellisation 75 4.6.1 Thermodynamics of Micellisation 75

Contents ix 4.6.2 Factors Affecting the CMC 78 4.6.3 Structure of Micelles and Molecular Packing 80 4.7 Liquid Crystalline Mesophases 82 4.7.1 Definition 82 4.7.2 Structures 83 4.7.3 Phase Diagrams 86 4.8 Advanced Surfactants 87 References 88 Microemulsions 91 Julian Eastoe 5.1 Introduction 91 5.2 Microemulsions: Definition and History 91 5.3 Theory of Formation and Stability 93 5.3.1 Interfacial Tension in Microemulsions 93 5.3.2 Kinetic Instability 95 5.4 Physicochemical Properties 95 5.4.1 Predicting Microemulsion Type 95 5.4.2 Surfactant Film Properties 101 5.4.3 Phase Behaviour 107 5.5 Developments and Applications 110 5.5.1 Microemulsions with Green and Novel Solvents 110 5.5.2 Microemulsions as Reaction Media for Nanoparticles 113 References 114 Emulsions Brian Vincent 6.1 Introduction 6.1.1 Definitions of Emulsion Type 6.1.2 Novel Features of Emulsion Systems, Compared to Solid/Liquid Dispersions 6.2 Preparation 6.2.1 6.2.2 6.2.3 6.3 Stability 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6 References Comminution - Batch Comminution - Continuous Nucleation and Growth Introduction Sedimentation and Creaming Aggregation Coalescence Ostwald Ripening Phase Inversion 117 117 117 120 120 120 124 124 126 126 126 127 128 130 131 133

x Contents Polymers and Polymer Solutions 135 Terence Cosgrove 7.1 Introduction 135 7.2 Polymerisation 135 7.2.1 Condensation 136 7.2.2 Free Radical 136 7.2.3 Ionic Methods 137 7.3 Copolymers 137 7.4 Polymer Physical Properties 138 7.4.1 Entanglements 138 7.5 Polymer Uses 138 7.6 Theoretical Models of Polymer Structure 138 7.6.1 Radius of Gyration 139 7.6.2 Worm-like Chains 141 7.6.3 Radius of Gyration in Ideal Solution 142 7.6.4 Excluded Volume 142 7.6.5 Scaling Theory: Blobs 143 7.6.6 Polyelectrolytes 144 7.7 Measuring Polymer Molecular Weight 144 7.7.1 Viscosity 146 7.8 Flory-Huggins Theory 146 7.8.1 Polymer Solutions 146 7.8.2 Polymer Melts 150 7.8.3 Copolymers 150 References 150 Polymers at Interfaces 151 Terence Cosgrove 8.1 Introduction 151 8.1.1 Steric Stability 152 8.1.2 The Size and Shape of Polymers in Solution 152 8.1.3 Adsorption of Small Molecules 154 8.2 Adsorption of Polymers 155 8.2.1 Configurational Entropy 155 8.2.2 The Flory Surface Parameter ^s 155 8.3 Models and Simulations for Terminally Attached Chains 156 8.3.1 Atomistic Modelling 156 8.3.2 Exact Enumeration: Terminally Attached Chains 157 8.3.3 Approximate Methods: Terminally Attached Chains 160 8.3.4 Scaling Models for Terminally Attached Chains (Brushes) 160 8.3.5 Physically Adsorbed Chains: Scheutjens and Fleer Theory 161 8.3.6 Scaling Theory for Physical Adsorption 165 8.4 Experimental Aspects 166 8.4.1 Volume Fraction Profiles 166 8.4.2 Adsorption Isotherms 167

Contents xi 8.4.3 The Bound Fraction 170 8.4.4 The Layer Thickness 171 8.5 Copolymers 175 8.5.1 Liquid/Liquid Interfaces 176 8.6 Polymer Brushes 177 8.7 Conclusions 179 References 180 9 Effect of Polymers on Colloid Stability 181 Jeroen van Duijneveldt 9.1 Introduction 181 9.1.1 Colloid Stability 181 9.1.2 Limitations of Charge Stabilisation 182 9.1.3 Effect of Polymers on Interactions 182 9.2 Particle Interaction Potential 182 9.2.1 Measuring Surface Forces 183 9.3 Steric Stabilisation 183 9.3.1 Theory 183 9.3.2 Steric Stabiliser Design 186 9.3.3 Marginal Solvents 187 9.4 Depletion Interactions 189 9.5 Bridging Interactions 192 9.6 Conclusion 193 References 194 10 Wetting of Surfaces 197 Paul Reynolds 10.1 Introduction 197 10.2 Surfaces and Definitions 198 10.3 Surface Tension 198 10.4 Surface Energy 199 10.5 Contact Angles 199 10.6 Wetting 200 10.7 Liquid Spreading and Spreading Coefficients 202 10.8 Cohesion and Adhesion 203 10.9 Two Liquids on a Surface 204 10.10 Detergency 207 10.11 Spreading of a Liquid on a Liquid 207 10.12 Characterisation of a Solid Surface 210 10.13 Polar and Dispersive Components 210 10.14 Polar Materials 211 10.15 Wettability Envelopes 212 10.16 Measurement Methods 214 10.17 Conclusions 216 References 216

Contents Aerosols 219 Nana-Owusua A. Kwamena and Jonathan P. Reid 11.1 Introduction 219 11.2 Generating and Sampling Aerosols 222 11.2.1 Generating Aerosols 222 11.2.2 Sampling Aerosol 224 11.3 Determining the Particle Concentration and Size 225 11.3.1 Determining the Number Concentration 226 11.3.2 Determining the Mass Concentration 226 11.3.3 Determining Particle Size 227 11.4 Determining Particle Composition 230 11.4.1 Off-line Analysis 230 11.4.2 Real-time Analysis 231 11.5 The Equilibrium State of Aerosols 234 11.5.1 Deliquescence and Efflorescence 234 11.5.2 Köhler Theory 235 11.5.3 Measurements of Hygroscopic Growth 237 11.5.4 Other Phases 238 11.6 The Kinetics of Aerosol Transformation 238 11.6.1 Steady and Unsteady Mass and Heat Transfer 239 11.6.2 Uptake of Trace Species and Heterogeneous Chemistry 240 11.7 Concluding Remarks 242 References 242 Practical Rheology Roy Hughes 12.1 12.2 Introduction Making Measurements 245 245 12.2.1 12.2.2 12.2.3 12.2.4 12.2.5 Definitions Designing an Experiment Geometries Viscometry Shear Thinning and Thickening Behaviour 246 248 250 252 254 12.3 Rheometry and Viscoelasticity 256 12.3.1 12.3.2 12.3.3 12.3.4 12.3.5 Viscoelasticity and Deborah Number Oscillation and Linearity Creep Compliance Liquid and Solid Behaviour Sedimentation and Storage Stability 256 257 258 259 261 12.4 Examples of Soft Materials 263 12.4.1 12.4.2 12.4.3 12.4.4 Simple Particles and Polymers Networks and Functionalisation Polymeric Additives Particle Additives 264 267 268 268 12.5 Summary 271 References 272 245

Contents xiii 13 Scattering and Reflection Techniques 273 Robert Richardson 13.1 Introduction 273 13.2 The Principle of a Scattering Experiment 274 13.3 Radiation for Scattering Experiments 275 13.4 Light Scattering 276 13.5 Dynamic Light Scattering 278 13.6 Small Angle Scattering 279 13.7 Sources of Radiation 279 13.8 Small Angle Scattering Apparatus 280 13.9 Scattering and Absorption by Atoms 282 13.10 Scattering Length Density 283 13.11 Small Angle Scattering from a Dispersion 284 13.12 Form Factor for Spherical Particles 285 13.13 Determining Particle Size from SANS and SAXS 285 13.14 Guinier Plots to Determine Radius of Gyration 286 13.15 Determination of Particle Shape 286 13.16 Polydispersity 287 13.17 Determination of Particle Size Distribution 288 13.18 Alignment of Anisotropic Particles 289 13.19 Concentrated Dispersions 289 13.20 Contrast Variation Using SANS 290 13.21 High Q Limit: Porod Law 292 13.22 Introduction to X-Ray and Neutron Reflection 294 13.23 Reflection Experiment 295 13.24 A Simple Example of a Reflection Measurement 295 13.25 Conclusion 297 References 297 14 Optical Manipulation 299 Paul Bartlett 14.1 Introduction 299 14.2 Manipulating Matter with Light 299 14.3 Force Generation in Optical Tweezers 302 14.4 Nanofabrication 304 14.5 Single Particle Dynamics 305 14.5.1 Measuring Nanometer Displacements 305 14.5.2 Brownian Fluctuations in an Optical Trap 306 14.5.3 Dynamical Complexity in Colloidal Gels 307 14.6 Conclusions 308 References 308 15 Electron Microscopy 311 Sean Davis 15.1 General Features of (Electron) Optical Imaging Systems 311

xiv Contents 15.2 Conventional ТЕМ 313 15.2.1 Background 313 15.2.2 Practical Aspects 314 15.2.3 Polymer Latex Particles 315 15.2.4 Core/Shell Particles 316 15.2.5 Internal Structure 317 15.3 Conventional SEM 321 15.3.1 Background 321 15.3.2 Types of Signal 321 15.3.3 Practical Aspects 321 15.4 Summary 327 References 327 16 Surface Forces 329 Wuge Briscoe 16.1 Introduction 329 16.1.1 Intermolecular Forces 329 16.1.2 From Intermolecular Forces to Surface Forces 330 16.1.3 Why Measure Surface Forces? 333 16.2 Forces and Energy; Size and Shape 334 16.2.1 Pressure, Force and Energy 334 16.2.2 The Derjaguin Approximation 335 16.3 Surface Force Measurement Techniques 339 16.3.1 Optical Tweezers 339 16.3.2 Total Internal Reflection Microscopy (TIRM) 340 16.3.3 Atomic Force Microscope (AFM) 340 16.3.4 Surface Force Apparatus (SFA) 341 16.3.5 Other Techniques 341 16.4 Different Types of Surface Forces 342 16.4.1 van der Waals Forces 343 16.4.2 Electric Double Layer Forces in a Polar Liquid 344 16.4.3 The DLVO Theory 345 16.4.4 Non-DLVO Forces 345 16.4.5 Neutral Polymer-mediated Surface Forces 352 16.4.6 Surface Forces in Surfactant Solutions 355 16.5 Recent Examples of Surface Force Measurement 356 16.5.1 Counter-ion Only (CIO) Electric Double Layer Interactions in a Non-polar Liquid 357 16.5.2 Interactions Between Surface-grown Biomimetic Polymer Brushes in Aqueous Media 358 16.5.3 Boundary Lubrication Under Water 358 16.6 Future Challenges 360 References 361 Index 363