Preface ........................................................ XV
1 General Introduction ......................................... 1
Further Reading .............................................. 5
2 General Classification of Surface-active Agents Used in
Agrochemical Formulations .................................... 7
2.1 Anionic Surfactants ..................................... 7
2.1.1 Carboxylates ..................................... 8
2.1.2 Sulfates ......................................... 8
2.1.3 Sulfonates ....................................... 9
2.1.4 Phosphate-containing Anionic Surfactants ........ 10
2.2 Cationic Surfactants ................................... 10
2.3 Amphoteric (Zwitterionic) Surfactants .................. 11
2.4 Nonionic Surfactants ................................... 12
2.4.1 Alcohol Ethoxylates ............................. 12
2.4.2 Alkylphenol Ethoxylates ......................... 13
2.4.3 Fatty Acid Ethoxylates .......................... 13
2.4.4 Sorbitan Esters and Their Ethoxylated
Derivatives (Spans and Tweens) .................. 14
2.4.5 Ethoxylated Fats and Oils ....................... 15
2.4.6 Amine Ethoxylates ............................... 15
2.4.7 Surfactants Derived from Mono- and
Polysaccharides ................................. 15
2.5 Speciality Surfactants - Fluorocarbon and Silicone
Surfactants ............................................ 16
2.6 Polymeric Surfactants .................................. 17
2.6.1 Ethylene Oxide-Propylene Oxide Copolymers
(EO/PO) ......................................... 17
References .................................................. 18
3 Physical Chemistry of Surfactant Solutions .................. 19
3.1 Properties of Solutions of Surfactants ................. 19
3.2 Solubility-Temperature Relationship for Surfactants .... 23
3.3 Thermodynamics of Micellization ........................ 25
3.3.1 Kinetic Aspects ................................. 25
3.3.2 Equilibrium Aspects: Thermodynamics of
Micellization ................................... 26
3.3.3 Phase Separation Model .......................... 27
3.3.4 Mass Action Model ............................... 28
3.3.5 Enthalpy and Entropy of Micellization ........... 30
3.3.6 Driving Force for Micelle Formation ............. 31
3.4 Micellization in Surfactant Mixtures (Mixed
Micelles) .............................................. 33
3.4.1 Surfactant Mixtures with No Net Interaction ..... 33
3.4.2 Surfactant Mixtures with a Net Interaction ...... 34
3.5 Surfactant-Polymer Interaction ......................... 35
3.5.1 Factors Influencing the Association Between
Surfactant and Polymer .......................... 36
3.5.2 Driving Force for Surfactant-Polymer
Interaction ..................................... 37
3.5.3 Structure of Surfactant-Polymer Complexes ....... 38
3.5.4 Surfactant-Нуdrophobically Modified Polymer
Interaction ..................................... 38
References ................................................. 39
4 Interfacial Aspects of Agrochemical Formulations ............ 41
4.1 Introduction ........................................... 41
4.2 Equilibrium Adsorption of Surfactants at the
Air/Liquid and Liquid/Liquid Interfaces ................ 41
4.3 The Gibbs Adsorption Isotherm .......................... 43
4.4 Dynamic Processes of Adsorption ........................ 46
4.4.1 General Theory of Adsorption Kinetics ........... 47
4.4.2 Adsorption Kinetics from Micellar Solutions ..... 49
4.4.3 Experimental Techniques for Studying
Adsorption Kinetics ............................. 51
4.4.3.1 The Drop Volume Technique .............. 51
4.4.3.2 Maximum Bubble Pressure Technique ...... 52
4.5 Adsorption of Surfactants and Polymeric Surfactants
at the Solid/Liquid Interface .......................... 55
4.6 Surfactant Adsorption .................................. 55
4.6.1 Adsorption of Ionic Surfactants on Hydrophobic
Surfaces ........................................ 56
4.6.2 Adsorption of Ionic Surfactants on Polar
Surfaces ........................................ 59
4.6.3 Adsorption of Nonionic Surfactants .............. 60
4.7 Adsorption of Polymeric Surfactants at the Solid/
Liquid Interface ....................................... 62
4.8 Experimental Methods for Measurement of Adsorption
Parameters for Polymeric Surfactants ................... 68
4.8.1 Amount of Polymer Adsorbed, Г - The Adsorption
Isotherms ....................................... 68
4.8.2 Polymer-bound Fraction p ........................ 71
4.8.3 Adsorbed Layer Thickness S and Segment Density
Distribution p(z) ............................... 72
4.8.4 Hydrodynamic Thickness Determination ............ 72
References ................................................. 74
4.8.1 5 Interaction Forces Between Particles or
Droplets in Agrochemical
5 Dispersions (Suspension Concentrates or Emulsions, EWs)
and Their Role in Colloid Stability ......................... 77
5.1 Introduction ........................................... 77
5.2 van der Waals Attraction ............................... 77
5.3 Electrical Double Layer Repulsion ...................... 79
5.4 Total Energy of Interaction: Deryaguin-Landau-Verwey-
Overbeek E rO) Theory .................................. 81
5.5 Criteriria for Stabilization of Dispersions with
Double Layer action .................................... 83
5.5.1 The Zeta Potential .............................. 83
5.6 Steric Stabilization of Dispersions .................... 85
5.7 Interaction Between Particles or Droplets Containing
Adsorbed Polymeric Surfactant Layers ................... 85
5.7.1 Mixing Interaction, Gmix ........................ 86
5.7.2 Elastic Interaction, Gel ........................ 87
5.7.3 Criteria for Effective Steric Stabilization ..... 89
5.8 Flocculation of Sterically Stabilized Dispersions ...... 90
References .................................................. 91
6 Emulsion Concentrates (EWs) ................................. 93
6.1 Introduction ........................................... 93
6.2 Formation of Emulsions ................................. 94
6.3 Mechanism of Emulsification ............................ 95
6.4 Methods of Emulsification .............................. 96
6.5 Role of Surfactants in Emulsion Formation .............. 97
6.5.1 Role of Surfactants in Droplet Deformation ...... 99
6.6 Selection of Emulsifiers .............................. 100
6.6.1 The Ну drophilic-Lipophilic Balance (HLB)
Concept ........................................ 100
6.6.2 The Phase Inversion Temperature (PIT)
Concept ........................................ 103
6.6.3 The Cohesive Energy Ratio (CER) Concept for
Emulsifier Selection ........................... 105
6.6.4 The Critical Packing Parameter (CPP) for
Emulsifier Selection ........................... 107
6.6.5 Emulsion Stability ............................. 108
6.7 Creaming or Sedimentation of Emulsions ................ 109
6.7.1 Creaming or Sedimentation Rates ................ 110
6.7.1.1 Very Dilute Emulsions (Ø < 0.01) ...... 110
6.7.1.2 Moderately Concentrated Emulsions
(0.2 < Ø < 0.1) ....................... 110
6.7.1.3 Concentrated Emulsions (Ø > 0.2) ...... 111
6.7.2 Prevention of Creaming or Sedimentation ........ 111
6.7.2.1 Matching Density of Oil and Aqueous
Phases ................................ 111
6.7.2.2 Reduction of Droplet Size ............. 111
6.7.2.3 Use of'Thickeners' .................... 112
6.7.2.4 Controlled Flocculation ............... 113
6.7.2.5 Depletion Flocculation ................ 113
6.8 Flocculation of Emulsions ............................. 114
6.8.1 General Rules for Reducing (Eliminating)
Flocculation ................................... 115
6.8.1.1 Charge-stabilized Emulsions, e.g.
Using Ionic Surfactants ............... 115
6.8.1.2 Sterically Stabilized Emulsions ....... 115
6.9 Ostwald Ripening ...................................... 115
6.10 Coalescence of Emulsions .............................. 117
6.10.1 Rate of Coalescence ....................... 119
6.11 Phase Inversion ....................................... 119
6.12 Experimental Methods for Assessment of Emulsion
Stability ............................................. 120
6.12.1 Assessment of Creaming or Sedimentation ....... 121
6.12.2 Assessment of Emulsion Flocculation ........... 122
6.12.3 Assessment of Ostwald Ripening ................ 123
6.12.4 Assessment of Coalescence ..................... 123
6.12.5 Assessment of Phase Inversion ................. 123
References ................................................. 123
7 Suspension Concentrates (SCs) .............................. 125
7.1 Introduction .......................................... 125
7.2 Preparation of Suspension Concentrates and the Role
of Surfactants/Dispersing Agents ...................... 126
7.3 Wetting of the Agrochemical Powder .................... 126
7.3.1 Measurement of Contact Angles of Liquids and
Surfactant Solutions on Powders ................ 129
7.3.2 Dispersion and Milling ......................... 129
7.3.3 Effect of Surfactant Adsorption ................ 130
7.4 Control of the Physical Stability of Suspension
Concentrates .......................................... 132
7.4.1 Stability Against Aggregation .................. 136
7.4.2 Ostwald Ripening (Crystal Growth) .............. 138
7.4.3 Stability Against Claying or Caking ............ 139
7.4.4 Settling of Suspensions ........................ 139
7.4.5 Prevention of Settling and Claying ............. 144
7.4.5.1 Balance of the Density of Disperse
Phase and Medium ...................... 144
7.4.5.2 Use of High Molecular Weight
Polymers ('Thickeners') ............... 144
7.4.5.3 Use of 'Inert' Fine Particles ......... 145
7.4.5.4 Use of Mixtures of Polymers and
Finely Divided Solids ................. 146
7.4.6 Controlled Flocculation ........................ 146
7.4.7 Depletion Flocculation ......................... 146
7.5 Characterization of Suspension Concentrates and
Assessment of Their Long-term Physical Stability ...... 147
7.5.1 Assessment of the Structure of the Solid/
Liquid Interface ............................... 148
7.5.1.1 Double Layer Investigations ........... 148
7.5.1.2 Surfactant and Polymer Adsorption ..... 149
7.5.2 Assessment of the State of the Dispersion ...... 149
7.5.2.1 Measurement of Rate of Flocculation ... 149
7.5.2.2 Measurement of Incipient
Flocculation .......................... 150
7.5.2.3 Measurement of Crystal Growth
(Ostwald Ripening) .................... 150
7.6 Bulk Properties of Suspension Concentrates ............ 151
7.6.1 Equilibrium Sediment Volume (or Height) and
Redispersion ................................... 151
7.6.2 Rheological Measurements ....................... 151
7.6.2.1 Assessment of Sedimentation ........... 152
7.6.2.2 Assessment of Flocculation ............ 155
7.6.3 Time Effects During Flow - Thixotropy .......... 157
7.6.4 Constant Stress (Creep) Experiments ............ 158
7.6.5 Dynamic (Oscillatory) Measurements ............. 159
References ................................................. 164
8 Oil-based Suspension Concentrates .......................... 165
8.1 Introduction .......................................... 165
8.2 Stability of Suspensions in Polar Media ............... 166
8.3 Stability of Suspensions in Nonpolar Media ............ 168
8.3.1 Characterization of the Adsorbed Polymer
Layer .......................................... 169
8.4 Theory of Steric Stabilization ........................ 169
8.4.1 Criteria for Effective Steric Stabilization .... 172
8.5 Settling of Suspensions ............................... 172
8.5.1 Prevention of Formation of Dilatant
Sediments ...................................... 172
8.5.2 Examples of Suspending Agents That Can Be
Applied for Prevention of Settling in
Non-aqueous Suspensions ........................ 174
8.6 Emulsification of Oil-based Suspensions ............... 176
8.6.1 Mechanism of Spontaneous Emulsification and
the Role of Mixed Surfactant Film .............. 176
8.6.2 Polymeric Surfactants for Oil-based
Suspensions and the Choice ofEmulsifiers ....... 180
8.6.3 Emulsification into Aqueous Electrolyte
Solutions ...................................... 180
8.7 Proper Choice of the Antisettling System .............. 181
8.8 Rheological Characteristics of the Oil-based
Suspensions ........................................... 181
References ............................................ 182
9 Suspoemulsions ............................................. 183
9.1 Introduction .......................................... 178
9.2 Systems Investigated .................................. 184
9.3 Experimental Methods .................................. 185
9.4 Results and Discussion ................................ 185
9.4.1 Creaming/Sedimentation of Suspoemulsions ....... 185
9.4.2 Reduction of Interactions in Suspoemulsions .... 187
9.4.3 Reduction of Heteroflocculation ................ 188
9.4.4 Reduction of Emulsion Coalescence .............. 188
9.4.5 Summary of the Criteria for Preparation of
a Stable Suspoemulsion ......................... 189
9.4.6 Preparation of Suspoemulsion by
Emulsification of the Oil into the
Suspension ..................................... 189
9.4.7 Prevention of Crystallization .................. 190
9.4.8 Model Suspoemulsion of Polystyrene Latex and
Isoparaffmic Oil Stabilized with Synperonic
PE(PEO-PPO-PEO A-B-A Block Copolymer) .......... 191
9.4.9 Model Systems of Polystyrene Latex with
Grafted PEO Chains and Hexadecane Emulsions .... 192
9.5 Conclusions ........................................... 195
References ............................................ 196
10 Microemulsions ............................................. 197
10.1 Introduction .......................................... 197
10.2 Thermodynamic Definition of Microemulsions ............ 198
10.3 Application in Agrochemicals .......................... 199
10.4 Basic Principles of Microemulsion Formation and
Thermodynamic Stability ............................... 200
10.4.1 Mixed Film Theories ............................ 200
10.4.2 Solubilization Theories ........................ 202
10.4.3 Thermodynamic Theory of Microemulsion
Formation and Stability ........................ 204
10.4.4 Reason for Combining Two Surfactants ........... 205
10.4.5 Factors Determining W/O Versus O/W
Microemulsions ................................. 206
10.5 Characterization of Microemulsions Using Scattering
Techniques ............................................ 207
10.5.1 Time-averaged (Static) Light Scattering ........ 208
10.5.1.1 Calculation of Droplet Size from
Interfacial Area ...................... 210
10.5.2 Dynamic Light Scattering (Photon Correlation
Spectroscopy, PCS) ............................. 211
10.6 Characterization of Microemulsions Using
Conductivity .......................................... 222
10.7 NMR Measurements ...................................... 214
10.8 Selection of Surfactants for Formulation of
Microemulsions ........................................ 215
10.9 Role of Microemulsions in Enhancement of Biological
Efficacy .............................................. 215
References .................................................... 218
11 Multiple Emulsions ......................................... 219
11.1 Introduction .......................................... 219
11.1.1 Preparation of Multiple Emulsions .............. 219
11.1.2 Types of Multiple Emulsions .................... 220
11.1.3 Breakdown Processes of Multiple Emulsions ...... 221
11.1.4 Factors Affecting Stability of Multiple
Emulsions and Criteria for Their
Stabilization .................................. 222
11.2 General Description of Polymeric Surfactants .......... 223
11.3 Interaction Between Oil or Water Droplets Containing
an Adsorbed Polymeric Surfactant - Steric
Stabilization ......................................... 225
11.4 Examples of Multiple Emulsions Using Polymeric
Surfactants ........................................... 232
References ................................................. 233
12 Controlled-release Formulations ............................ 235
12.1 Introduction .......................................... 235
12.2 Microencapsulation .................................... 235
12.3 Mechanism of Release of Active Ingredient from
Microcapsules ......................................... 237
12.4 Encapsulation by Phase Separation from Aqueous
Solution .............................................. 237
12.5 Microencapsulation of Solid Particles ................. 238
12.6 Controlled Release of Agrochemicals from Matrix-
based Microparticles .................................. 239
12.7 Mechanism of Controlled Release from Microparticles ... 240
12.8 Controlled Release from Granules ...................... 242
References ................................................... 245
13 Basic Principles of Selection of Adjuvants in
Agrochemical Formulations .................................. 247
13.1 I ntroduction ......................................... 247
13.2 Interactions at the Air/Solution Interface and Their
Effect on Droplet Formation ........................... 251
13.3 Spray Impaction and Adhesion .......................... 255
13.4 Droplet Sliding and Spray Retention ................... 258
13.5 Wetting and Spreading ................................. 262
13.6 Evaporation of Spray Drops and Deposit Formation ...... 266
13.7 Solubilization and its Effect on Transport ............ 268
13.8 Interaction Between Surfactant, Agrochemical and
Target Species ........................................ 271
References ................................................. 272
Subject Index ................................................. 273
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