An Introduction to Surfactants (eBook)

lt;!doctype html public "-//w3c//dtd html 4.0 transitional//en">

Thatwat F. Tadros, Wokingham, UK.

Tharwat F. Tadros, Wokingham, UK.

Preface 5
1 General introduction 13
2 General classification of surfactants 17
2.1 Anionic surfactants 17
2.1.1 Carboxylates 18
2.1.2 Sulfates 18
2.1.3 Sulfonates 19
2.1.4 Isethionates 20
2.1.5 Taurates 21
2.1.6 Phosphate-containing anionic surfactants 21
2.2 Cationic surfactants 21
2.3 Amphoteric (zwitterionic) surfactants 23
2.4 Nonionic surfactants 24
2.4.1 Alcohol ethoxylates 24
2.4.2 Alkyl phenol ethoxylates 25
2.4.3 Fatty acid ethoxylates 25
2.4.4 Sorbitan esters and their ethoxylated derivatives (Spans and Tweens) 25
2.4.5 Ethoxylated fats and oils 27
2.4.6 Amine ethoxylates 27
2.4.7 Amine oxides 27
2.5 Speciality surfactants 28
2.5.1 Fluorocarbon and silicone surfactants 28
2.5.2 Gemini surfactants 29
2.5.3 Surfactants derived from mono- and polysaccharides 29
2.5.4 Naturally occurring surfactants 30
2.5.5 Biosurfactants 34
2.5.6 Polymeric surfactants 36
3 Aggregation of surfactants, self-assembly structures, liquid crystalline phases 41
3.1 Thermodynamics of micellization 48
3.1.1 Kinetic aspects 48
3.1.2 Equilibrium aspects: Thermodynamics of micellization 49
3.2 Enthalpy and entropy of micellization 51
3.3 Driving force for micelle formation 52
3.4 Micellization in surfactant mixtures (mixed micelles) 54
3.5 Surfactant self-assembly 57
3.5.1 Structure of liquid crystalline phases 57
3.5.2 Hexagonal phase 58
3.5.3 Micellar cubic phase 59
3.5.4 Lamellar phase 59
3.5.5 Bicontinuous cubic phases 59
3.5.6 Reversed structures 59
3.6 Experimental studies of the phase behavior of surfactants 60
4 Surfactant adsorption at interfaces 63
4.1 Introduction 63
4.2 Adsorption of surfactants at the air/liquid (A/L) and liquid/liquid (L/L)interfaces 64
4.2.1 The Gibbs adsorption isotherm 65
4.2.2 Equation of state approach 69
4.2.3 The Langmuir, Szyszkowski and Frumkin equations 70
4.3 Interfacial tension measurements 71
4.3.1 The Wilhelmy plate method 71
4.3.2 The pendent drop method 72
4.3.3 The Du Nouy’s ring method 73
4.3.4 The drop volume (weight) method 73
4.3.5 The spinning drop method 73
4.4 Adsorption of surfactants at the solid/liquid interface 74
4.4.1 Adsorption of ionic surfactants on hydrophobic surfaces 76
4.4.2 Adsorption of ionic surfactants on polar surfaces 79
4.4.3 Adsorption of nonionic surfactants 81
5 Surfactants as emulsifiers 85
5.1 Introduction 85
5.1.1 Nature of the emulsifier 85
5.1.2 Structure of the system 86
5.1.3 Breakdown processes in emulsions 86
5.2 Physical chemistry of emulsion systems 89
5.2.1 The interface (Gibbs dividing line) 89
5.2.2 Thermodynamics of emulsion formation and breakdown 90
5.2.3 Interaction energies (forces) between emulsion droplets and their combinations 92
5.3 Mechanism of emulsification 97
5.3.1 Methods of emulsification 98
5.3.2 Role of surfactants in emulsion formation 100
5.3.3 Role of surfactants in droplet deformation 101
5.4 Selection of emulsifiers 104
5.4.1 The Hydrophilic-Lipophile Balance (HLB) concept 104
5.4.2 The Phase Inversion Temperature (PIT) concept 107
5.5 Stabilization of emulsions 109
5.5.1 Creaming or sedimentation and its prevention 109
5.5.2 Flocculation of emulsions and its prevention 110
5.5.3 Ostwald ripening and its reduction 111
5.5.4 Emulsion coalescence and its prevention 112
6 Surfactants as dispersants and stabilization of suspensions 115
6.1 Introduction 115
6.2 Role of surfactants in preparation of solid/liquid dispersions (suspensions) 115
6.2.1 Role of surfactants in condensation methods. Nucleation and growth 116
6.2.2 Emulsion polymerization 117
6.2.3 Dispersion polymerization 119
6.2.4 Role of surfactants in dispersion methods 121
6.3 Assessment of wettability of powders 127
6.3.1 Sinking time, submersion or immersion test 127
6.3.2 Measurement of contact angles of liquids and surfactant solutions on powders 128
6.3.3 List of wetting agents for hydrophobic solids in water 128
6.3.4 Stabilization of suspensions using surfactants 130
7 Surfactants for foam stabilization 133
7.1 Introduction 133
7.2 Foam preparation 133
7.3 Foam structure 134
7.4 Classification of foam stability 135
7.4.1 Drainage and thinning of foam films 136
7.4.2 Theories of foam stability 137
7.5 Foam inhibitors 141
7.5.1 Chemical inhibitors that lower viscosity and increase drainage 142
7.5.2 Solubilized chemicals which cause antifoaming 142
7.5.3 Droplets and oil lenses which cause antifoaming and defoaming 142
7.5.4 Surface tension gradients (induced by antifoamers) 143
7.5.5 Hydrophobic particles as antifoamers 143
7.5.6 Mixtures of hydrophobic particles and oils as antifoamers 144
7.6 Assessment of foam formation and stability 144
7.6.1 Efficiency and effectiveness of a foaming surfactant 145
8 Surfactants in nanoemulsions 147
8.1 Introduction 147
8.2 Fundamental principles of emulsification 149
8.2.1 Methods of emulsification and the role of surfactants 150
8.3 Preparation of nanoemulsions 151
8.3.1 Use of high pressure homogenizers 151
8.3.2 Phase inversion principle methods (low energy emulsification) 152
8.4 Steric stabilization and the role of the adsorbed layer thickness 153
8.5 Ostwald Ripening 156
8.6 Examples of nanoemulsions 157
9 Surfactants in microemulsions 165
9.1 Introduction 165
9.2 Thermodynamic definition of microemulsions 166
9.3 Description of microemulsions using phase diagrams 167
9.4 Thermodynamic theory of microemulsion formation 169
9.5 Characterization of microemulsions using scattering techniques 171
9.5.1 Time average (static) light scattering 171
9.5.2 Dynamic light scattering (photon correlation spectroscopy, PCS) 174
9.6 Characterization of microemulsions using conductivity 175
9.7 NMR measurements 177
9.8 Formulation of microemulsions 177
10 Surfactants as wetting agents 181
10.1 Introduction 181
10.2 The concept of contact angle 182
10.3 Adhesion tension 184
10.4 Work of adhesionWa 184
10.5 Work of cohesion 184
10.6 The spreading coefficient S 185
10.7 Contact angle hysteresis 185
10.8 Critical surface tension of wetting 186
10.9 Effect of surfactant adsorption 187
10.10 Measurement of contact angles 188
11 Industrial applications of surfactants 191
11.1 Surfactants in the home, personal care and cosmetics 191
11.1.1 Shaving formulations 196
11.1.2 Bar soaps 197
11.1.3 Liquid hand soaps 197
11.1.4 Bath oils 198
11.1.5 Foam (or bubble) baths 198
11.1.6 After bath preparations 198
11.1.7 Skin care products 198
11.1.8 Hair care formulations 200
11.1.9 Sunscreens 203
11.1.10 Make-up products 205
11.2 Surfactants in pharmacy 208
11.2.1 Surface active drugs 209
11.2.2 Naturally occurring micelle-forming systems 210
11.2.3 Biological implications of the presence of surfactants in pharmaceutical formulations 212
11.2.4 Solubilized systems 213
11.2.5 Pharmaceutical aspects of solubilization 214
11.3 Surfactants in agrochemicals 214
11.4 Surfactants in paints and coatings 224
11.5 Surfactants in detergents 229
Index 233