Table of Contents
Preface v
1 General introduction 1
2 General classification of surfactants 5
2.1 Anionic surfactants 5
2.1.1 Carboxytates 6
2.1.2 Sulfates 6
2.1.3 Sulfonates 7
2.1.4 Isethionates 8
2.1.5 Taurates 9
2.1.6 Phosphate-containing anionic surfactants 9
2.2 Cationic surfactants 9
2.3 Amphoteric (zwitterionic) surfactants 11
2.4 Nonionic surfactants 12
2.4.1 Alcohol ethoxytates 12
2.4.2 Alky I phenol ethoxylates 13
2.4.3 Fatty acid ethoxylates 13
2.4.4 Sorbitan esters and their ethoxylated derivatives (Spans and Tweens) 13
2.4.5 Ethoxylated fats and oils 15
2.4.6 Amine ethoxylates 15
2.4.7 Amine oxides 15
2.5 Speciality surfactants 16
2.5.1 Fluorocarbon and silicone surfactants 16
2.5.2 Gemini surfactants 17
2.5.3 Surfactants derived from mono- and polysaccharides 17
2.5.4 Naturally occurring surfactants 18
2.5.5 Biosurfactants 22
2.5.6 Polymeric surfactants 24
3 Aggregation of surfactants, self-assembly structures, liquid crystalline phases 29
3.1 Thermodynamics of micellization 36
3.1.1 Kinetic aspects 36
3.1.2 Equilibrium aspects: Thermodynamics of micellization 37
3.2 Enthalpy and entropy of micellization 39
3.3 Driving force for micelle formation 40
3.4 Micellization in surfactant mixtures (mixed micelles) 42
3.5 Surfactant self-assembly 45
3.5.1 Structure of liquid crystalline phases 45
3.5.2 Hexagonal phase 46
3.5.3 Micellar cubic phase 47
3.5.4 Lamellar phase 47
3.5.5 Bicontinuous cubic phases 47
3.5.6 Reversed structures 47
3.6 Experimental studies of the phase behavior of surfactants 48
4 Surfactant adsorption at interfaces 51
4.1 Introduction 51
4.2 Adsorption of surfactants at the air/liquid (A/L) and liquid/liquid (L/L) interfaces 52
4.2.1 The Gibbs adsorption isotherm 53
4.2.2 Equation of state approach 57
4.2.3 The Langmuir, Szyszkowski and Frumkin equations 58
4.3 Interfacial tension measurements 59
4.3.1 The Wilhelmy plate method 59
4.3.2 The pendent drop method 60
4.3.3 The Du Nouy's ring method 61
4.3.4 The drop volume (weight) method 61
4.3.5 The spinning drop method 61
4.4 Adsorption of surfactants at the solid/liquid interface 62
4.4.1 Adsorption of ionic surfactants on hydrophobic surfaces 64
4.4.2 Adsorption of ionic surfactants on polar surfaces 67
4.4.3 Adsorption of nonionic surfactants 69
5 Surfactants as emulsifiers 73
5.1 Introduction 73
5.1.1 Nature of the emulsifier 73
5.1.2 Structure of the system 74
5.1.3 Breakdown processes in emulsions 74
5.2 Physical chemistry of emulsion systems 77
5.2.1 The interface (Gibbs dividing line) 77
5.2.2 Thermodynamics of emulsion formation and breakdown 78
5.2.3 Interaction energies (forces) between emulsion droplets and their combinations 80
5.3 Mechanism of emulsification 85
5.3.1 Methods of emulsification 86
5.3.2 Role of surfactants in emulsion formation 88
5.3.3 Role of surfactants in droplet deformation 89
5.4 Selection of emulsifiers 92
5.4.1 The Hydrophilic-Lipophile Balance (HLB) concept 92
5.4.2 The Phase Inversion Temperature (PIT) concept 95
5.5 Stabilization of emulsions 97
5.5.1 Creaming or sedimentation and its prevention 97
5.5.2 Flocculation of emulsions and its prevention 98
5.5.3 Ostwald ripening and its reduction 99
5.5.4 Emulsion coalescence and its prevention 100
6 Surfactants as dispersants and stabilization of suspensions 103
6.1 Introduction 103
6.2 Role of surfactants in preparation of solid/liquid dispersions (suspensions) 103
6.2.1 Role of surfactants in condensation methods. Nucleation and growth 104
6.2.2 Emulsion polymerization 105
6.2.3 Dispersion polymerization 107
6.2.4 Role of surfactants in dispersion methods 109
6.3 Assessment of wettability of powders 115
6.3.1 Sinking time, submersion or immersion test 115
6.3.2 Measurement of contact angles of liquids and surfactant solutions on powders 116
6.3.3 List of wetting agents for hydrophobic solids in water 116
6.3.4 Stabilization of suspensions using surfactants 118
7 Surfactants for foam stabilization 121
7.1 Introduction 121
7.2 Foam preparation 121
7.3 Foam structure 122
7.4 Classification of foam stability 123
7.4.1 Drainage and thinning of foam films 124
7.4.2 Theories of foam stability 125
7.5 Foam inhibitors 129
7.5.1 Chemical inhibitors that lower viscosity and increase drainage 130
7.5.2 Solubilized chemicals which cause antifoaming 130
7.5.3 Droplets and oil lenses which cause antifoaming and defoaming 130
7.5.4 Surface tension gradients (induced by antifoamers) 131
7.5.5 Hydrophobic particles as antifoamers 131
7.5.6 Mixtures of hydrophobic particles and oils as antifoamers 132
7.6 Assessment of foam formation and stability 132
7.6.1 Efficiency and effectiveness of a foaming surfactant 133
8 Surfactants in nanoemulsions 135
8.1 Introduction 135
8.2 Fundamental principles of emulsification 137
8.2.1 Methods of emulsification and the role of surfactants 138
8.3 Preparation of nanoemulsions 139
8.3.1 Use of high pressure homogenizers 139
8.3.2 Phase inversion principle methods (low energy emulsification) 140
8.4 Steric stabilization and the role of the adsorbed layer thickness 141
8.5 Ostwald Ripening 144
8.6 Examples of nanoemulsions 145
9 Surfactants in microemulsions 153
9.1 Introduction 153
9.2 Thermodynamic definition of microemulsions 154
9.3 Description of microemulsions using phase diagrams 155
9.4 Thermodynamic theory of microemulsion formation 157
9.5 Characterization of microemulsions using scattering techniques 159
9.5.1 Time average (static) light scattering 159
9.5.2 Dynamic light scattering (photon correlation spectroscopy, PCS) 162
9.6 Characterization of microemulsions using conductivity 163
9.7 NMR measurements 165
9.8 Formulation of microemulsions 165
10 Surfactants as wetting agents 169
10.1 Introduction 169
10.2 The concept of contact angle 170
10.3 Adhesion tension 172
10.4 Work of adhesion Wa 172
10.5 Work of cohesion 172
10.6 The spreading coefficient S 173
10.7 Contact angle hysteresis 173
10.8 Critical surface tension of wetting 174
10.9 Effect of surfactant adsorption 175
10.10 Measurement of contact angles 176
11 Industrial applications of surfactants 179
11.1 Surfactants in the home, personal care and cosmetics 179
11.1.1 Shaving formulations 184
11.1.2 Bar soaps 185
11.1.3 Liquid hand soaps 185
11.1.4 Bath oils 186
11.1.5 Foam (or bubble) baths 186
11.1.6 After bath preparations 186
11.1.7 Skin care products 186
11.1.8 Hair care formulations 188
11.1.9 Sunscreens 191
11.1.10 Make-up products 193
11.2 Surfactants in pharmacy 196
11.2.1 Surface active drugs 197
11.2.2 Naturally occurring micelle-forming systems 198
11.2.3 Biological implications of the presence of surfactants in pharmaceutical formulations 200
11.2.4 Solubilized systems 201
11.2.5 Pharmaceutical aspects of solubilization 202
11.3 Surfactants in agrochemicals 202
11.4 Surfactants in paints and coatings 212
11.5 Surfactants in detergents 217
Index 221
