Introduction to Applied Colloid and Surface Chemistry

Colloid and Surface Chemistry is a subject of immense importance and implications both to our everyday life and numerous industrial sectors, ranging from coatings and materials to medicine and biotechnology. How do detergents really clean? (Why can't we just use water?) Why is milk "milky"? Why do we use eggs so often for making sauces? Can we deliver drugs in better and controlled ways? Coating industries wish to manufacture improved coatings e.g. for providing corrosion resistance, which are also environmentally friendly i.e. less based on organic solvents and if possible exclusively on water. Food companies want to develop healthy, tasty but also long-lasting food products which appeal to the environmental authorities and the consumer. Detergent and enzyme companies are working to develop improved formulations which clean more persistent stains, at lower temperatures and amounts, to the benefit of both the environment and our pocket. Cosmetics is also big business! Creams, lotions and other personal care products are really just complex emulsions. All of the above can be explained by the principles and methods of colloid and surface chemistry. A course on this topic is truly valuable to chemists, chemical engineers, biologists, material and food scientists and many more.

Table of Contents:
Preface xi Useful Constants xvi Symbols and Some Basic Abbreviations xvii About the Companion Web Site xx 1 Introduction to Colloid and Surface Chemistry 1 1.1 What are the colloids and interfaces? Why are they important? Why do we study them together? 1 1.1.1 Colloids and interfaces 3 1.2 Applications 4 1.3 Three ways of classifying the colloids 5 1.4 How to prepare colloid systems 6 1.5 Key properties of colloids 7 1.6 Concluding remarks 7 Appendix 1.1 8 Problems 9 References 10 2 Intermolecular and Interparticle Forces 11 2.1 Introduction – Why and which forces are of importance in colloid and surface chemistry? 11 2.2 Two important long-range forces between molecules 12 2.3 The van der Waals forces 15 2.3.1 Van der Waals forces between molecules 15 2.3.2 Forces between particles and surfaces 16 2.3.3 Importance of the van der Waals forces 21 2.4 Concluding remarks 25 Appendix 2.1 A note on the uniqueness of the water molecule and some of the recent debates on water structure and peculiar properties 26 References for the Appendix 2.1 28 Problems 29 References 33 3 Surface and Interfacial Tensions – Principles and Estimation Methods 34 3.1 Introduction 34 3.2 Concept of surface tension – applications 34 3.3 Interfacial tensions, work of adhesion and spreading 39 3.3.1 Interfacial tensions 39 3.3.2 Work of adhesion and cohesion 43 3.3.3 Spreading coefficient in liquid–liquid interfaces 44 3.4 Measurement and estimation methods for surface tensions 45 3.4.1 The parachor method 46 3.4.2 Other methods 48 3.5 Measurement and estimation methods for interfacial tensions 50 3.5.1 “Direct” theories (Girifalco–Good and Neumann) 51 3.5.2 Early “surface component” theories (Fowkes, Owens–Wendt, Hansen/Skaarup) 52 3.5.3 Acid–base theory of van Oss–Good (van Oss et al., 1987) – possibly the best theory to-date 57 3.5.4 Discussion 59 3.6 Summary 60 Appendix 3.1 Hansen solubility parameters (HSP) for selected solvents 61 Appendix 3.2 The “φ” parameter of the Girifalco–Good equation (Equation 3.16) for liquid–liquid interfaces. Data from Girifalco and Good (1957, 1960) 66 Problems 67 References 72 4 Fundamental Equations in Colloid and Surface Science 74 4.1 Introduction 74 4.2 The Young equation of contact angle 74 4.2.1 Contact angle, spreading pressure and work of adhesion for solid–liquid interfaces 74 4.2.2 Validity of the Young equation 77 4.2.3 Complexity of solid surfaces and effects on contact angle 78 4.3 Young–Laplace equation for the pressure difference across a curved surface 79 4.4 Kelvin equation for the vapour pressure, P, of a droplet (curved surface) over the “ordinary” vapour pressure Psat for a flat surface 80 4.4.1 Applications of the Kelvin equation 81 4.5 The Gibbs adsorption equation 82 4.6 Applications of the Gibbs equation (adsorption, monolayers, molecular weight of proteins) 83 4.7 Monolayers 86 4.8 Conclusions 89 Appendix 4.1 Derivation of the Young–Laplace equation 90 Appendix 4.2 Derivation of the Kelvin equation 91 Appendix 4.3 Derivation of the Gibbs adsorption equation 91 Problems 93 References 95 5 Surfactants and Self-assembly. Detergents and Cleaning 96 5.1 Introduction to surfactants – basic properties, self-assembly and critical packing parameter (CPP) 96 5.2 Micelles and critical micelle concentration (CMC) 99 5.3 Micellization – theories and key parameters 106 5.4 Surfactants and cleaning (detergency) 112 5.5 Other applications of surfactants 113 5.6 Concluding remarks 114 Appendix 5.1 Useful relationships from geometry 115 Appendix 5.2 The Hydrophilic–Lipophilic Balance (HLB) 116 Problems 117 References 119 6 Wetting and Adhesion 121 6.1 Introduction 121 6.2 Wetting and adhesion via the Zisman plot and theories for interfacial tensions 122 6.2.1 Zisman plot 122 6.2.2 Combining theories of interfacial tensions with Young equation and work of adhesion for studying wetting and adhesion 124 6.2.3 Applications of wetting and solid characterization 130 6.3 Adhesion theories 141 6.3.1 Introduction – adhesion theories 141 6.3.2 Adhesive forces 144 6.4 Practical adhesion: forces, work of adhesion, problems and protection 147 6.4.1 Effect of surface phenomena and mechanical properties 147 6.4.2 Practical adhesion – locus of failure 148 6.4.3 Adhesion problems and some solutions 149 6.5 Concluding remarks 154 Problems 155 References 160 7 Adsorption in Colloid and Surface Science – A Universal Concept 161 7.1 Introduction – universality of adsorption – overview 161 7.2 Adsorption theories, two-dimensional equations of state and surface tension–concentration trends: a clear relationship 161 7.3 Adsorption of gases on solids 162 7.3.1 Adsorption using the Langmuir equation 163 7.3.2 Adsorption of gases on solids using the BET equation 164 7.4 Adsorption from solution 168 7.4.1 Adsorption using the Langmuir equation 168 7.4.2 Adsorption from solution – the effect of solvent and concentration on adsorption 171 7.5 Adsorption of surfactants and polymers 173 7.5.1 Adsorption of surfactants and the role of CPP 173 7.5.2 Adsorption of polymers 174 7.6 Concluding remarks 179 Problems 180 References 184 8 Characterization Methods of Colloids – Part I: Kinetic Properties and Rheology 185 8.1 Introduction – importance of kinetic properties 185 8.2 Brownian motion 185 8.3 Sedimentation and creaming (Stokes and Einstein equations) 187 8.3.1 Stokes equation 187 8.3.2 Effect of particle shape 188 8.3.3 Einstein equation 190 8.4 Kinetic properties via the ultracentrifuge 191 8.4.1 Molecular weight estimated from kinetic experiments (1 = medium and 2 = particle or droplet) 193 8.4.2 Sedimentation velocity experiments (1 = medium and 2 = particle or droplet) 193 8.5 Osmosis and osmotic pressure 193 8.6 Rheology of colloidal dispersions 194 8.6.1 Introduction 194 8.6.2 Special characteristics of colloid dispersions’ rheology 196 8.7 Concluding remarks 198 Problems 198 References 201 9 Characterization Methods of Colloids – Part II: Optical Properties (Scattering, Spectroscopy and Microscopy) 202 9.1 Introduction 202 9.2 Optical microscopy 202 9.3 Electron microscopy 204 9.4 Atomic force microscopy 206 9.5 Light scattering 207 9.6 Spectroscopy 209 9.7 Concluding remarks 210 Problems 210 References 210 10 Colloid Stability – Part I: The Major Players (van der Waals and Electrical Forces) 211 10.1 Introduction – key forces and potential energy plots – overview 211 10.1.1 Critical coagulation concentration 213 10.2 van der Waals forces between particles and surfaces – basics 214 10.3 Estimation of effective Hamaker constants 215 10.4 vdW forces for different geometries – some examples 217 10.4.1 Complex fluids 219 10.5 Electrostatic forces: the electric double layer and the origin of surface charge 219 10.6 Electrical forces: key parameters (Debye length and zeta potential) 222 10.6.1 Surface or zeta potential and electrophoretic experiments 223 10.6.2 The Debye length 225 10.7 Electrical forces 228 10.7.1 Effect of particle concentration in a dispersion 229 10.8 Schulze–Hardy rule and the critical coagulation concentration (CCC) 230 10.9 Concluding remarks on colloid stability, the vdW and electric forces 233 10.9.1 vdW forces 233 10.9.2 Electric forces 234 Appendix 10.1 A note on the terminology of colloid stability 235 Appendix 10.2 Gouy–Chapman theory of the diffuse electrical double-layer 236 Problems 238 References 242 11 Colloid Stability – Part II: The DLVO Theory – Kinetics of Aggregation 243 11.1 DLVO theory – a rapid overview 243 11.2 DLVO theory – effect of various parameters 244 11.3 DLVO theory – experimental verification and applications 245 11.3.1 Critical coagulation concentration and the Hofmeister series 245 11.3.2 DLVO, experiments and limitations 247 11.4 Kinetics of aggregation 255 11.4.1 General – the Smoluchowski model 255 11.4.2 Fast (diffusion-controlled) coagulation 255 11.4.3 Stability ratio W 255 11.4.4 Structure of aggregates 257 11.5 Concluding remarks 264 Problems 265 References 268 12 Emulsions 269 12.1 Introduction 269 12.2 Applications and characterization of emulsions 269 12.3 Destabilization of emulsions 272 12.4 Emulsion stability 273 12.5 Quantitative representation of the steric stabilization 275 12.5.1 Temperature-dependency of steric stabilization 276 12.5.2 Conditions for good stabilization 277 12.6 Emulsion design 278 12.7 PIT – Phase inversion temperature of emulsion based on non-ionic emulsifiers 279 12.8 Concluding remarks 279 Problems 280 References 282 13 Foams 283 13.1 Introduction 283 13.2 Applications of foams 283 13.3 Characterization of foams 285 13.4 Preparation of foams 287 13.5 Measurements of foam stability 287 13.6 Destabilization of foams 288 13.6.1 Gas diffusion 289 13.6.2 Film (lamella) rupture 290 13.6.3 Drainage of foam by gravity 291 13.7 Stabilization of foams 293 13.7.1 Changing surface viscosity 293 13.7.2 Surface elasticity 293 13.7.3 Polymers and foam stabilization 295 13.7.4 Additives 296 13.7.5 Foams and DLVO theory 296 13.8 How to avoid and destroy foams 296 13.8.1 Mechanisms of antifoaming/defoaming 297 13.9 Rheology of foams 299 13.10 Concluding remarks 300 Problems 301 References 302 14 Multicomponent Adsorption 303 14.1 Introduction 303 14.2 Langmuir theory for multicomponent adsorption 304 14.3 Thermodynamic (ideal and real) adsorbed solution theories (IAST and RAST) 306 14.4 Multicomponent potential theory of adsorption (MPTA) 312 14.5 Discussion. Comparison of models 315 14.5.1 IAST – literature studies 315 14.5.2 IAST versus Langmuir 315 14.5.3 MPTA versus IAST versus Langmuir 317 14.6 Conclusions 317 Acknowledgments 319 Appendix 14.1 Proof of Equations 14.10a,b 319 Problems 319 References 320 15 Sixty Years with Theories for Interfacial Tension – Quo Vadis? 321 15.1 Introduction 321 15.2 Early theories 321 15.3 van Oss–Good and Neumann theories 331 15.3.1 The two theories in brief 331 15.3.2 What do van Oss–Good and Neumann say about their own theories? 333 15.3.3 What do van Oss–Good and Neumann say about each other’s theories? 334 15.3.4 What do others say about van Oss–Good and Neumann theories? 335 15.3.5 What do we believe about the van Oss–Good and Neumann theories? 338 15.4 A new theory for estimating interfacial tension using the partial solvation parameters (Panayiotou) 339 15.5 Conclusions – Quo Vadis? 344 Problems 345 References 349 16 Epilogue and Review Problems 352 Review Problems in Colloid and Surface Chemistry 353 Index 358