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Formulation of Disperse Systems: Science and Technology

ISBN: 978-3-527-33682-1
504 pages
August 2014
Formulation of Disperse Systems: Science and Technology  (3527336826) cover image

Description

This book presents comprehensively the science and technology behind the formulation of disperse systems like emulsions, suspensions, foams and others. Starting with a general introduction, the book covers a broad range of topics like the role of different classes of surfactants, stability of disperse systems, formulation of different dispersions, evaluation of formulations and many more. Many examples are included, too. Written by the experienced author and editor Tharwart Tadros, this book is indispensable for every scientist working in the field.

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Table of Contents

Preface XVII

1 General Introduction 1

1.1 Suspensions 1

1.2 Latexes 2

1.3 Emulsions 2

1.4 Suspoemulsions 3

1.5 Multiple Emulsions 3

1.6 Nanosuspensions 4

1.7 Nanoemulsions 4

1.8 Microemulsions 5

1.9 Pigment and Ink Dispersions 5

1.10 Foams 5

References 9

2 Surfactants Used in Formulation of Dispersions 11

2.1 General Classification of Surface-Active Agents 12

2.1.1 Anionic Surfactants 13

2.1.1.1 Carboxylates 13

2.1.1.2 Sulphates 14

2.1.1.3 Sulphonates 15

2.1.1.4 Phosphate-Containing Anionic Surfactants 16

2.1.2 Cationic Surfactants 16

2.1.3 Amphoteric (Zwitterionic) Surfactants 17

2.1.4 Nonionic Surfactants 18

2.1.4.1 Alcohol Ethoxylates 19

2.1.4.2 Alkyl Phenol Ethoxylates 19

2.1.4.3 Fatty Acid Ethoxylates 20

2.1.4.4 Sorbitan Esters and Their Ethoxylated Derivatives (Spans and Tweens) 20

2.1.4.5 Ethoxylated Fats and Oils 21

2.1.4.6 Amine Ethoxylates 21

2.1.4.7 Amine Oxides 21

2.1.5 Specialty Surfactants 22

2.1.5.1 Fluorocarbon and Silicone Surfactants 22

2.1.5.2 Gemini Surfactants 23

2.1.5.3 Surfactants Derived from Monosaccharides and Polysaccharides 23

References 24

3 Physical Chemistry of Surfactant Solutions and the Process of Micellisation 27

3.1 Thermodynamics of Micellisation 33

3.1.1 Kinetic Aspects 34

3.1.2 Equilibrium Aspects: Thermodynamics of Micellisation 35

3.2 Enthalpy and Entropy of Micellisation 37

3.2.1 Driving Force for Micelle Formation 38

3.2.2 Micellisation in Surfactant Mixtures (Mixed Micelles) 40

References 43

4 Dispersants and Polymeric Surfactants 45

4.1 Solution Properties of Polymeric Surfactants 46

4.2 General Classification of Polymeric Surfactants 50

4.3 Polyelectrolytes 53

References 54

5 Adsorption of Surfactants at the Air/Liquid, Liquid/Liquid, and Solid/Liquid Interfaces 55

5.1 Introduction 55

5.2 Adsorption of Surfactants at the Air/Liquid (A/L) and Liquid/Liquid (L/L) Interfaces 56

5.3 The Gibbs Adsorption Isotherm 57

5.4 Equation of State Approach 60

5.5 The Langmuir, Szyszkowski, and Frumkin Equations 62

5.6 Interfacial Tension Measurements 63

5.6.1 The Wilhelmy Plate Method 63

5.6.2 The Pendant Drop Method 64

5.6.3 The Du Nouy’s Ring Method 64

5.6.4 The Drop Volume (Weight) Method 65

5.6.5 The Spinning Drop Method 65

5.7 Adsorption of Surfactants at the Solid/Liquid (S/L) Interface 66

5.7.1 Adsorption of Ionic Surfactants on Hydrophobic Surfaces 68

5.7.2 Adsorption of Ionic Surfactants on Polar Surfaces 71

5.7.3 Adsorption of Nonionic Surfactants 72

References 74

6 Adsorption of Polymeric Surfactants at the Solid/Liquid Interface 77

6.1 Theories of Polymer Adsorption 80

6.2 Experimental Techniques for Studying Polymeric Surfactant Adsorption 88

6.2.1 Measurement of the Adsorption Isotherm 88

6.2.2 Measurement of the Fraction of Segments, p 89

6.3 Determination of Segment Density Distribution ρ(z) and Adsorbed Layer Thickness δh 89

6.4 Examples of the Adsorption Isotherms of Nonionic Polymeric Surfactants 92

6.4.1 Adsorbed Layer Thickness Results 96

6.4.2 Kinetics of Polymer Adsorption 98

References 98

7 Colloid Stability of Disperse Systems Containing Electrical Double Layers 101

7.1 Origin of Charge on Surfaces 101

7.1.1 Surface Ions 101

7.1.2 Isomorphic Substitution 102

7.2 Structure of the Electrical Double Layer 103

7.2.1 Diffuse Double layer (Gouy and Chapman) 103

7.3 Stern–Grahame Model of the Double Layer 104

7.4 Distinction between Specific and Nonspecific Adsorbed Ions 104

7.5 Electrical Double Layer Repulsion 105

7.6 van der Waals Attraction 106

7.7 Total Energy of Interaction 109

7.7.1 Deryaguin–Landau–Verwey–Overbeek (DLVO) Theory 109

7.8 Flocculation of Suspensions 111

7.9 Criteria for Stabilisation of Dispersions with Double Layer Interaction 113

References 114

8 Stability of Disperse Systems Containing Adsorbed Nonionic Surfactants or Polymers: Steric Stabilisation 115

8.1 Introduction 115

8.2 Interaction between Particles Containing Adsorbed Nonionic and Polymeric Surfactant Layers (Steric Stabilisation) 116

8.3 Mixing Interaction Gmix 117

8.4 Elastic Interaction Gel 118

8.5 Total Energy of Interaction 119

8.6 Criteria for Effective Steric Stabilisation 120

8.7 Flocculation of Sterically Stabilised Dispersions 121

8.7.1 Weak Flocculation 121

8.7.2 Incipient Flocculation 121

8.7.3 Depletion Flocculation 122

References 123

9 Formulation of Solid/Liquid Dispersions (Suspensions) 125

9.1 Introduction 125

9.2 Preparation of Suspensions 126

9.3 Condensation Methods: Nucleation and Growth 126

9.4 Dispersion Methods 128

9.4.1 Wetting of Powders by Liquids 129

9.4.2 Structure of the Solid/Liquid Interface and the Electrical Double Layer 131

9.4.2.1 Electrical Double Layer Repulsion 132

9.4.2.2 van der Waals Attraction 132

9.4.2.3 Total Energy of Interaction 133

9.4.2.4 Criteria for Stabilisation of Suspensions with Double Layer Interaction 135

9.4.2.5 Electrokinetic Phenomena and the Zeta-Potential 135

9.4.2.6 Calculation of the Zeta-Potential 136

9.4.2.7 Measurement of the Zeta-Potential 137

9.4.3 Dispersing Agents for Formulation of Suspensions 139

9.4.4 Adsorption of Surfactants at the Solid/Liquid Interface 139

9.4.5 Steric Stabilisation of Suspensions 141

9.4.6 Flocculation of Sterically Stabilised Suspensions 143

9.4.7 Properties of Concentrated Suspensions 144

9.4.8 Characterisation of Suspensions and Assessment of their Stability 149

9.4.8.1 Optical Microscopy 150

9.4.8.2 Electron Microscopy 151

9.4.8.3 Confocal Laser Scanning Microscopy 151

9.4.8.4 Scattering Techniques 151

9.5 Bulk Properties of Suspensions 152

9.5.1 Rheological Measurements 152

9.5.2 Sedimentation of Suspensions and Prevention of Formation of Dilatant Sediments (Clays) 153

9.5.3 Prevention of Sedimentation and Formation of Dilatant Sediments 156

References 159

10 Formulation of Liquid/Liquid Dispersions (Emulsions) 161

10.1 Introduction 161

10.1.1 Creaming and Sedimentation 161

10.1.2 Flocculation 162

10.1.3 Ostwald Ripening (Disproportionation) 162

10.1.4 Coalescence 163

10.1.5 Phase Inversion 163

10.2 Industrial Applications of Emulsions 163

10.3 Physical Chemistry of Emulsion Systems 164

10.3.1 The Interface (Gibbs Dividing Line) 164

10.3.2 Thermodynamics of Emulsion Formation and Breakdown 165

10.3.3 Interaction Energies (Forces) between Emulsion Droplets and Their Combinations 166

10.3.3.1 van der Waals Attractions 166

10.3.3.2 Electrostatic Repulsion 167

10.3.3.3 Steric Repulsion 170

10.4 Adsorption of Surfactants at the Liquid/Liquid Interface 172

10.4.1 Mechanism of Emulsification 174

10.4.2 Methods of Emulsification 175

10.4.3 Role of Surfactants in Emulsion Formation 177

10.4.4 Role of Surfactants in Droplet Deformation 179

10.5 Selection of Emulsifiers 183

10.5.1 The Hydrophilic–Lipophilic Balance (HLB) Concept 183

10.5.2 The Phase Inversion Temperature (PIT) Concept 186

10.6 Creaming or Sedimentation of Emulsions 187

10.6.1 Creaming or Sedimentation Rates 188

10.6.1.1 Very Dilute Emulsions ( < 0.01) 188

10.6.1.2 Moderately Concentrated Emulsions (0.2 < < 0.1) 189

10.6.1.3 Concentrated Emulsions ( > 0.2) 189

10.6.2 Prevention of Creaming or Sedimentation 190

10.6.2.1 Matching the Density of Oil and Aqueous Phases 190

10.6.2.2 Reduction of Droplet Size 190

10.6.2.3 Use of ‘Thickeners’ 190

10.6.2.4 Controlled Flocculation 191

10.6.2.5 Depletion Flocculation 191

10.7 Flocculation of Emulsions 192

10.7.1 Mechanism of Emulsion Flocculation 193

10.7.1.1 Flocculation of Electrostatically Stabilised Emulsions 193

10.7.1.2 Flocculation of Sterically Stabilised Emulsions 195

10.8 General Rules for Reducing (Eliminating) Flocculation 196

10.8.1 Charge-Stabilised Emulsions (e.g., Using Ionic Surfactants) 196

10.8.2 Sterically Stabilised Emulsions 196

10.9 Ostwald Ripening 196

10.10 Emulsion Coalescence 198

10.10.1 Rate of Coalescence 200

10.11 Phase Inversion 200

References 201

11 Formulation of Suspoemulsions (Mixtures of Suspensions and Emulsions) 203

11.1 Introduction 203

11.2 Suspoemulsions in Paints 204

11.2.1 Suspoemulsions in Sunscreens and Colour Cosmetics 207

11.3 Suspoemulsions in Agrochemicals 219

11.3.1 Model Suspoemulsion of Polystyrene Latex and Isoparaffinic Oil stabilised with Synperonic PE (PEO–PPO–PEO A-B-A Block Copolymer) 225

11.3.2 Model Systems of Polystyrene Latex with Grafted PEO Chains and Hexadecane Emulsions 227

References 230

12 Formulation of Multiple Emulsions 231

12.1 Introduction 231

12.2 Preparation of Multiple Emulsions 232

12.3 Types of Multiple Emulsions 233

12.4 Breakdown Processes of Multiple Emulsions 233

12.5 Factors Affecting Stability of Multiple Emulsions, and Criteria for Their Stabilisation 235

12.6 General Description of Polymeric Surfactants 237

12.7 Interaction between Oil or Water Droplets Containing an Adsorbed Polymeric Surfactant: Steric Stabilisation 238

12.8 Examples of Multiple Emulsions Using Polymeric Surfactants 246

12.9 Characterisation of Multiple Emulsions 247

12.9.1 Droplet Size Measurements 247

12.10 Rheological Measurements 248

References 249

13 Preparation of Nanosuspensions 251

13.1 Introduction 251

13.2 Nucleation and Growth, and Control of Particle Size Distribution 252

13.3 Preparation of Nanosuspensions by Bottom-Up Processes 254

13.3.1 Solvent–Antisolvent Method 255

13.3.2 Use of a Nanoemulsion 255

13.3.3 Mixing Two Microemulsions 256

13.3.4 Preparation of Polymer Nanoparticles by Miniemulsion or Minisuspension polymerisation 256

13.4 Preparation of Nanosuspensions Using the Bottom-Down Process 257

13.4.1 Wetting of the Bulk Powder 257

13.4.2 Breaking of Aggregates and Agglomerates into Individual Units 260

13.4.3 Wet Milling or Comminution 260

13.4.4 Stabilisation of the Resulting Dispersion 261

13.4.5 Prevention of Ostwald Ripening (Crystal Growth) 268

References 268

14 Formulation of Nanoemulsions 271

14.1 Introduction 271

14.2 Mechanism of Emulsification 273

14.3 Methods of Emulsification and the Role of Surfactants 275

14.4 Preparation of Nanoemulsions 276

14.4.1 High-Pressure Homogenisation 276

14.4.2 Phase Inversion Composition (PIC) Principle 277

14.4.3 Phase Inversion Temperature (PIT) Principle 277

14.4.4 Preparation of Nanoemulsions by Dilution of Microemulsions 279

14.5 Steric Stabilisation and the Role of the Adsorbed Layer Thickness 281

14.5.1 Ostwald Ripening 283

14.5.2 Practical Examples of Nanoemulsions 284

14.5.3 Nanoemulsions Based on Polymeric Surfactants 293

References 299

15 Formulation of Microemulsions 301

15.1 Introduction 301

15.2 Thermodynamic Definition of Microemulsions 302

15.3 Mixed-Film and Solubilisation Theories of Microemulsions 303

15.3.1 Mixed-Film Theories 303

15.3.2 Solubilisation Theories 305

15.4 Thermodynamic Theory of Microemulsion Formation 307

15.4.1 Reason for Combining Two Surfactants 308

15.4.2 Factors Determining W/O versus O/W Microemulsions 309

15.5 Characterisation of Microemulsions Using Scattering Techniques 311

15.5.1 Time-Average (Static) Light Scattering 311

15.5.2 Calculation of Droplet Size from Interfacial Area 313

15.5.3 Dynamic Light Scattering (Photon Correlation Spectroscopy; PCS) 314

15.6 Characterisation of Microemulsions Using Conductivity 315

15.7 NMR Measurements 316

15.8 Formulation of Microemulsions 317

15.8.1 The HLB System 318

15.8.2 Phase Inversion Temperature (PIT) Method 319

15.8.3 The Cohesive Energy Ratio (CER) Concept 320

15.8.4 Cosurfactant Partitioning 322

References 322

Further Reading 323

16 Formulation of Foams 325

16.1 Introduction 325

16.2 Foam Preparation 326

16.3 Foam Structure 327

16.4 Classification of Foam Stability 328

16.5 Drainage and Thinning of Foam Films 329

16.6 Theories of Foam Stability 330

16.6.1 Surface Viscosity and Elasticity Theory 330

16.6.2 The Gibbs–Marangoni Effect Theory 330

16.6.3 Surface Forces Theory (Disjoining Pressure π) 331

16.6.4 Stabilisation by Micelles (High Surfactant Concentrations > cmc) 334

16.6.5 Stabilisation by Lamellar Liquid Crystalline Phases 334

16.6.6 Stabilisation of Foam Films by Mixed Surfactants 334

16.7 Foam Inhibitors 335

16.7.1 Chemical Inhibitors That Lower Viscosity and Increase Drainage 335

16.7.2 Solubilised Chemicals Which Cause Antifoaming 335

16.7.3 Droplets and Oil Lenses Which Cause Antifoaming and Defoaming 336

16.7.4 Surface Tension Gradients (Induced by Antifoamers) 336

16.7.5 Hydrophobic Particles as Antifoamers 337

16.7.6 Mixtures of Hydrophobic Particles and Oils as Antifoamers 338

16.8 Physical Properties of Foams 338

16.8.1 Mechanical Properties 338

16.8.2 Rheological Properties 339

16.8.3 Electrical Properties 340

16.8.4 Electrokinetic Properties 340

16.8.5 Optical Properties 341

16.9 Experimental Techniques for Studying Foams 341

16.9.1 Studies on Foam Films 341

16.9.2 Structural Parameters of Foams 342

16.9.3 Foam Drainage 342

16.9.4 Foam Collapse 343

References 343

17 Formulation of Latexes 345

17.1 Introduction 345

17.2 Emulsion Polymerisation 346

17.2.1 Mechanism of Emulsion Polymerisation 348

17.2.2 Block Copolymers as Stabilisers in Emulsion Polymerisation 349

17.2.3 Graft Copolymers as Stabilisers in Emulsion Polymerisation 352

17.3 Polymeric Surfactants for Stabilisation of Preformed Latex Dispersions 356

17.4 Dispersion Polymerisation 360

17.4.1 Mechanism of Dispersion Polymerisation 362

17.4.2 Influence of Polymeric Surfactant Concentration and Molecular Weight on Particle Formation 363

17.4.3 Effect of Monomer Solubility and Concentration in the Continuous Phase 363

17.4.4 Stability/Instability of the Resulting Latex 364

17.4.5 Particle Formation in Polar Media 364

References 365

18 Formulation of Pigment and Ink Dispersions 367

18.1 Introduction 367

18.2 Powder Wetting 370

18.2.1 Effect of Surfactant Adsorption 374

18.2.2 Wetting of Powders by Liquids 375

18.2.3 Measurement of Wettability of Powders 377

18.2.3.1 Submersion Test: Sinking Time or Immersion Time 377

18.2.4 Measurement of Contact Angles of Liquids and Surfactant Solutions on Powders 378

18.2.5 Wetting Agents for Hydrophobic Pigments 379

18.2.6 Dynamics of Processing of Adsorption and Wetting 380

18.2.7 Experimental Techniques for Studying Adsorption Kinetics 384

18.3 Breaking of Aggregates and Agglomerates (Deagglomeration) 387

18.4 Classification of Dispersants 388

18.4.1 Surfactants 388

18.4.2 Polymeric Surfactants 389

18.4.3 Polyelectrolytes 390

18.4.4 Assessment and Selection of Dispersants 391

18.4.4.1 Adsorption Isotherms 391

18.4.4.2 Measurement of Dispersion and Particle Size Distribution 392

18.4.4.3 Wet Milling (Comminution) 392

18.4.4.4 Bead Mills 394

References 395

19 Methods of Evaluating Formulations after Dilution 397

19.1 Introduction 397

19.2 Assessment of the Structure of the Solid/Liquid Interface 398

19.2.1 Double Layer Investigation 398

19.2.1.1 Analytical Determination of Surface Charge 398

19.2.1.2 Electrokinetic and Zeta-Potential Measurements 399

19.2.2 Measurement of Surfactant and Polymer Adsorption 400

19.3 Assessment of Sedimentation of Suspensions 403

19.4 Assessment of Flocculation and Ostwald Ripening (Crystal Growth) 405

19.4.1 Optical Microscopy 406

19.4.1.1 Phase-Contrast Microscopy 406

19.4.1.2 Differential Interference Contrast (DIC) microscopy 407

19.4.1.3 Polarised Light Microscopy 407

19.4.1.4 Sample Preparation for Optical Microscopy 407

19.4.1.5 Particle Size Measurements Using Optical Microscopy 407

19.4.2 Electron Microscopy 408

19.4.2.1 Transmission Electron Microscopy 408

19.4.2.2 Scanning Electron Microscopy 409

19.4.3 Confocal Laser Scanning Microscopy 409

19.4.4 Scanning Probe Microscopy 409

19.4.5 Scanning Tunneling Microscopy 410

19.4.6 Atomic Force Microscopy 410

19.5 Scattering Techniques 411

19.5.1 Light-Scattering 411

19.5.1.1 Time-Average Light Scattering 411

19.5.1.2 Rayleigh–Gans–Debye Regime (RGD) λ/20 < R < λ 412

19.5.2 Turbidity Measurements 412

19.5.3 Light-Diffraction Techniques 413

19.5.4 Dynamic Light Scattering (DLS): Photon Correlation Spectroscopy (PCS) 415

19.5.5 Back-Scattering Techniques 418

19.6 Measurement of Rate of Flocculation 418

19.7 Measurement of Incipient Flocculation 419

19.8 Measurement of Crystal Growth (Ostwald Ripening) 420

19.9 Bulk Properties of Suspensions: Equilibrium Sediment Volume (or Height) and Redispersion 420

References 421

20 Evaluating Formulations without Dilution: Rheological Techniques 423

20.1 Introduction 423

20.2 Steady-State Measurements 424

20.2.1 Rheological Models for Analysis of Flow Curves 424

20.2.1.1 Newtonian Systems 424

20.2.1.2 Bingham Plastic Systems 425

20.2.1.3 Pseudoplastic (Shear Thinning) System 425

20.2.1.4 Dilatant (Shear Thickening) System 425

20.2.1.5 Herschel–Bulkley General Model 426

20.2.1.6 The Casson Model 426

20.2.1.7 The Cross Equation 426

20.2.2 Time Effects during Flow: Thixotropy and Negative (or Anti-) Thixotropy 426

20.3 Constant Stress (Creep) Measurements 429

20.3.1 Analysis of Creep Curves 430

20.3.1.1 Viscous Fluid 430

20.3.1.2 Elastic Solid 430

20.3.2 Viscoelastic Response 430

20.3.2.1 Viscoelastic Liquid 430

20.3.2.2 Viscoelastic Solid 431

20.3.3 Creep Procedure 431

20.4 Dynamic (Oscillatory) Measurements 432

20.4.1 Analysis of Oscillatory Response for a Viscoelastic System 433

20.4.2 Vector Analysis of the Complex Modulus 434

20.4.2.1 Dynamic viscosity η′ 434

20.4.2.2 Strain Sweep 434

20.4.2.3 Frequency Sweep 434

20.4.3 The Cohesive Energy Density Ec 436

20.4.4 Application of Rheological Techniques to Assess and Predict the Physical Stability of Suspensions 436

20.4.4.1 Rheological Techniques to Assess Sedimentation and Syneresis 436

20.4.4.2 Role of Thickeners 437

20.4.5 Assessment of Flocculation Using Rheological Techniques 438

20.4.5.1 Strain Sweep Measurements 440

20.4.5.2 Oscillatory Sweep Measurements 441

References 442

Further Reading 442

21 Assessment and Prediction of Creaming, Sedimentation, Flocculation, and Coalescence of Formulations 443

21.1 Assessment and Prediction of Creaming and Sedimentation 443

21.1.1 Introduction 443

21.1.2 Accelerated Tests and Their Limitations 443

21.1.3 Application of High-Gravity (g) Forces 444

21.1.4 Rheological Techniques for Prediction of Sedimentation or Creaming 445

21.1.5 Separation of Formulation (‘‘Syneresis’’) 445

21.1.6 Examples of Correlation of Sedimentation or Creaming with Residual (Zero Shear) Viscosity 446

21.1.6.1 Model Suspensions of Aqueous Polystyrene Latex 446

21.1.6.2 Sedimentation in Non-Newtonian Liquids 448

21.1.6.3 Role of Thickeners 448

21.1.6.4 Prediction of Emulsion Creaming 449

21.1.6.5 Creep Measurements for Prediction of Creaming 450

21.1.6.6 Oscillatory Measurements for Prediction of Creaming 451

21.2 Assessment and Prediction of Flocculation Using Rheological Techniques 452

21.2.1 Introduction 452

21.2.2 Wall Slip 452

21.2.3 Steady-State Shear Stress-Shear Rate Measurements 452

21.2.4 Influence of Ostwald Ripening and Coalescence 453

21.2.5 Constant Stress (Creep) Experiments 453

21.2.6 Dynamic (Oscillatory) Measurements 454

21.2.6.1 Strain Sweep Measurements 454

21.2.6.2 Oscillatory Sweep Measurements 455

21.2.7 Examples of the Application of Rheology for Assessment and Prediction of Flocculation 456

21.2.7.1 Flocculation and Restabilisation of Clays Using Cationic Surfactants 456

21.2.7.2 Flocculation of Sterically Stabilised Dispersions 457

21.2.7.3 Flocculation of Sterically Stabilised Emulsions 458

21.3 Assessment and Prediction of Emulsion Coalescence Using Rheological Techniques 459

21.3.1 Introduction 459

21.3.2 Rate of Coalescence 459

21.3.3 Rheological Techniques 460

21.3.3.1 Viscosity Measurements 460

21.3.3.2 Measurement of Yield Value as a Function of Time 461

21.3.3.3 Measurement of Storage Modulus G′ as a Function of Time 461

21.3.4 Correlation between Elastic Modulus and Coalescence 462

21.3.5 Cohesive Energy Ec 463

References 463

Index 465

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Author Information

Tharwat F. Tadros is a consultant for various chemical industries. After finishing his PhD at Alexandria University, he was appointed lecturer in Physical Chemistry (1962-1966) at the same university. Between 1966 and 1969, he spent a sabbatical at the Agricultural University of Wageningen and T.N.O in Delft, the Netherlands. Thereafter he worked at I.C.I. and ZENECA until 1994, where he researched various fields of surfactants, emulsions, suspensions, microemulsions, wetting spreading and adhesion, and rheology. During that period he was also appointed visiting professor at Imperial College London, Bristol University and Reading University. In 1992, he was elected President of the International Association of Colloid and Interface Science. Since leaving ZENECA, Dr. Tadros has worked as a consultant and also given several courses in his specialized field. He is the recipient of two medals from the Royal Society of Chemistry in the UK, and has more than 250 scientific papers to his name.
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