Introduction to Applied Colloid and Surface Chemistry

Georgios M. Kontogeorgis and Søren Kiil are both at the Technical University of Denmark, in the Dept of Chemical and Biochemical Engineering. Kontogeorgis is Professor of Applied Thermodynamics, and Kiil is Associate Professor in Coatings Science and Engineering. Prof Kontogeorgis has been teaching the colloid and surface chemistry course for 12 years, for the past 3 co-teaching with Kiil. Both authors have diverse research interests in strongly interconnected fields. Kontogeorgis' research interests are in the fields of thermodynamics, physical chemistry (especially surface science and polymers), while Kiil’s interests are primarily in coatings science and engineering (antifouling-, anticorrosive-, wind turbine blades etc). Both have valuable books publishing experience: Kontogeorgis most recently on thermodynamic models (2010, Wiley); and Kiil has co-authored a textbook on product design (2007, Wiley).

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