Emulsions: Formation, Stability, Industrial Applications

Emulsions: Formation, Stability, Industrial Applications

by Tharwat F. Tadros

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Product Details

ISBN-13: 9783110452174
Publisher: De Gruyter
Publication date: 03/21/2016
Series: De Gruyter Textbook Series
Pages: 242
Product dimensions: 6.69(w) x 9.45(h) x (d)
Age Range: 18 Years

About the Author

Tharwat F. Tadros, Wokingham, UK.

Table of Contents

Preface v

1 Emulsions: Formation, stability, industrial applications 1

1.1 General introduction 1

1.2 Nature of the Emulsifier 1

1.3 Structure of the system 2

1.4 Breakdown processes in emulsions 3

1.5 Creaming and sedimentation 4

1.6 Flocculation 4

1.7 Ostwald ripening (disproportionation) 4

1.8 Coalescence 5

1.9 Phase inversion 5

1.10 Industrial applications of emulsions 5

1.11 Book outline 6

2 Thermodynamics of emulsion formation and breakdown 9

2.1 The interface (Gibbs dividing line) 9

2.2 Thermodynamics of emulsion formation and breakdown 11

3 Interaction forces between emulsion droplets 15

3.1 Van der Waals attraction 15

3.2 Electrostatic repulsion 17

3.3 Steric repulsion 21

3.3.1 Mixing interaction Gmix 23

3.3.2 Elastic interaction Gel 24

3.3.3 Total energy of interaction 25

3.3.4 Criteria for effective steric stabilization 26

4 Adsorption of surfactants at the oil/water interface 29

4.1 Introduction 29

4.2 The Gibbs adsorption isotherm 29

4.3 Equation of state ppproach 32

4.4 The Langmuir, Szyszkowski and Frumkin equations 34

4.5 Effectiveness of surfactant adsorption at the liquid/liquid interface 35

4.6 Efficiency of adsorption of surfactant at the liquid/liquid interface 35

4.7 Adsorption from mixtures of two surfactants 37

4.8 Adsorption of macromolecules 38

4.9 Interfacial tension measurements 40

4.9.1 The Wilhelmy plate method 40

4.9.2 The pendent drop method 41

4.9.3 Sessile drop method 42

4.9.4 The Du Nouy ring method 43

4.9.5 The drop volume (weight) method 43

4.9.6 The spinning drop method 44

5 Mechanism of emulsification and the role of the emulsifier 47

5.1 Introduction 47

5.2 Mechanism of emulsification 47

5.3 Role of surfactants in emulsion formation 50

5.3.1 Role of surfactants in reduction of droplet size 50

5.3.2 Role of surfactants in droplet deformation 53

6 Methods of emulsification 59

6.1 Introduction 59

6.2 Rotor-stator mixers 59

6.2.1 Toothed devices 59

6.2.2 Batch radial discharge mixers 60

6.2.3 Design and arrangement 61

6.3 Flow regimes 63

6.3.1 Laminar flow 64

6.3.2 Turbulent flow 66

6.4 Membrane emulsification 69

6.5 Formulation variables and comparison of various emulsification methods 70

7 Selection of emulsifiers 73

7.1 Introduction 73

7.2 The hydrophilic-lipophile balance (HLB) concept 76

7.3 The phase inversion temperature (PIT) concept 82

7.4 The cohesive energy ratio (CER) concept 85

7.5 The critical packing parameter (CPP) for emulsion selection 86

7.6 Stabilisation by solid particles (Pickering emulsions) 89

8 Creaming/sedimentation of emulsions and its prevention 95

8.1 Introduction 95

8.2 Creaming or sedimentation rates 96

8.2.1 Very dilute emulsions (φ < 0.01) 96

8.2.2 Moderately concentrated emulsions (0.2 > φ > o.1) 97

8.2.3 Concentrated emulsions (φ > 0.2) 98

8.3 Properties of a creamed layer 98

8.4 Prevention of creaming or sedimentation 99

8.4.1 Matching density of oil and aqueous phases 99

8.4.2 Reduction of droplet size 99

8.4.3 Use of "thickeners" 100

8.4.4 Reduction of creaming/sedimentation of emulsions using associative thickeners 103

8.4.5 Controlled flocculation 106

8.4.6 Depletion flocculation 107

8.4.7 Use of "inert" fine particles 109

8.4.8 Use of mixtures of polymers and finely divided particulate solids 110

8.4.9 Use of liquid crystalline phases 111

9 Flocculation of emulsions 113

9.1 Introduction 113

9.2 Mechanism of emulsion flocculation 113

9.2.1 Flocculation of electrostatically stabilised emulsions 114

9.2.2 Flocculation of sterically stabilised emulsions 118

9.2.3 Weak flocculation of sterically stabilised emulsions 122

9.2.4 Depletion flocculation 123

9.2.5 Bridging flocculation by polymers and polyelectrolytes 124

9.3 General rules for reducing (eliminating) flocculation 127

9.3.1 Charge stabilised emulsions, e.g. using ionic surfactants 127

9.3.2 Sterically stabilised emulsions 127

10 Ostwald ripening in emulsions and its prevention 129

10.1 Driving force for Ostwald ripening 129

10.2 Kinetics of Ostwald ripening 130

10.3 Reduction of Ostwald ripening 134

10.3.1 Addition of a small proportion of highly insoluble oil 134

10.3.2 Modification of the interfacial layer for reduction of Ostwald ripening 136

10.4 Influence of initial droplet size of emulsions on the Ostwald ripening rate 137

11 Emulsion coalescence and its prevention 141

11.1 Introduction 141

11.2 Forces across liquid films 141

11.2.1 Disjoining pressure approach 143

11.2.2 Interfacial tension of liquid films 143

11.3 Film rupture 144

11.4 Rate of coalescence between droplets 146

11.5 Reduction of coalescence 151

11.5.1 Use of mixed surfactant films 151

12 Phase inversion and its prevention 161

12.1 Introduction 161

12.2 Catastrophic inversion 161

12.3 Transitional inversion 163

12.4 The phase inversion temperature (PIT) 165

13 Characterization of emulsions and assessment of their stability 173

13.1 Introduction 173

13.2 Assessment of the structure of the liquid/liquid interface 174

13.2.1 Double layer investigation 174

13.2.2 Measurement of surfactant and polymer adsorption 176

13.3 Assessment of creaming/sedimentation of emulsions 177

13.4 Assessment of flocculation, Ostwald ripening and coalescence 180

13.4.1 Optical microscopy 180

13.4.2 Electron microscopy 182

13.4.3 Confocal laser scanning microscopy (CLSM) 184

13.5 Scattering techniques 184

13.5.1 Light-scattering techniques 184

13.5.2 Turbidity measurements 185

13.5.3 Light diffraction techniques 186

13.5.4 Dynamic tight scattering - photon correlation spectroscopy (PCS) 188

13.5.5 Back-scattering techniques 191

13.6 Measurement of the rate of creaming or sedimentation 191

13.7 Measurement of rate of flocculation 192

13.8 Measurement of incipient flocculation 193

13.9 Measurement of Ostwald ripening 193

13.10 Measurement of the rate of coalescence 194

13.11 Bulk properties of emulsions. Equilibrium cream or sediment volume (or height) 194

14 Industrial applications of emulsions 197

14.1 Introduction 197

14.2 Food emulsions 197

14.2.1 Food grade surfactants 198

14.2.2 Surfactant association structures, micro-emulsions and emulsions in food 207

14.3 Emulsions in cosmetics and personal care formulations 209

14.4 Emulsions in pharmacy 217

14.5 Emulsions in agrochemicals 219

14.6 Rolling oil and lubricant emulsions 220

Index 223

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