Colloids in Agrochemicals: Colloids and Interface Science, Volume 5

293 Pages·2009·2.354 MB·English

by  Prof. Dr. Tharwat F. Tadros(auth.), Tharwat F. Tadros(eds.)

ColloidsandInterfaceScienceSeries
Volume5
ColloidsinAgrochemicals
TharwatF.Tadros
ColloidsandInterfaceScienceSeries,Vol.5
ColloidsinAgrochemicals. TharwatF.Tadros
Copyright62009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:978-3-527-31465-2
Colloids and Interface Science Series
edited by Tharwat F. Tadros
Other Volumes
Volume 1: Colloid Stability – Part I
ISBN978-3-527-31462-1
Volume 2: Colloid Stability – Part II
ISBN978-3-527-31503-1
Volume 3: Colloid Stability and Application in Pharmacy
ISBN978-3-527-31463-8
Volume 4: Colloids in Cosmetics and Personal Care
ISBN978-3-527-31464-5
Forthcoming Volume
Volume 6: Colloids in Paints
ISBN978-3-527-31466-9
Complete Set
Colloids and Interface Science Series
Volumes1–6
ISBN978-3-527-31461-4
Colloids and Interface Science Series
Volume 5
Colloids in Agrochemicals
Colloids and Interface Science
Tharwat F.Tadros
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62009WILEY-VCHVerlagGmbH&Co.KGaA,
Weinheim
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ISBN 978-3-527-31465-2
Thisbookisdedicatedtomygrandchildren:
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VII
Contents
Preface XV
1 GeneralIntroduction 1
FurtherReading 5
2 GeneralClassificationofSurface-activeAgentsUsedin
AgrochemicalFormulations 7
2.1 AnionicSurfactants 7
2.1.1 Carboxylates 8
2.1.2 Sulfates 8
2.1.3 Sulfonates 9
2.1.4 Phosphate-containingAnionicSurfactants 10
2.2 CationicSurfactants 10
2.3 Amphoteric(Zwitterionic)Surfactants 11
2.4 NonionicSurfactants 12
2.4.1 AlcoholEthoxylates 12
2.4.2 AlkylphenolEthoxylates 13
2.4.3 FattyAcidEthoxylates 13
2.4.4 SorbitanEstersandTheirEthoxylatedDerivatives
(SpansandTweens) 14
2.4.5 EthoxylatedFatsandOils 15
2.4.6 AmineEthoxylates 15
2.4.7 SurfactantsDerivedfromMono-andPolysaccharides 15
2.5 SpecialitySurfactants – FluorocarbonandSiliconeSurfactants 16
2.6 PolymericSurfactants 17
2.6.1 EthyleneOxide–PropyleneOxideCopolymers(EO/PO) 17
References 18
3 PhysicalChemistryofSurfactantSolutions 19
3.1 PropertiesofSolutionsofSurfactants 19
3.2 Solubility–TemperatureRelationshipforSurfactants 23
3.3 ThermodynamicsofMicellization 25
ColloidsandInterfaceScienceSeries,Vol.5
ColloidsinAgrochemicals. TharwatF.Tadros
Copyright62009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:978-3-527-31465-2
VIII Contents
3.3.1 KineticAspects 25
3.3.2 EquilibriumAspects:ThermodynamicsofMicellization 26
3.3.3 PhaseSeparationModel 27
3.3.4 MassActionModel 28
3.3.5 EnthalpyandEntropyofMicellization 30
3.3.6 DrivingForceforMicelleFormation 31
3.4 MicellizationinSurfactantMixtures(MixedMicelles) 33
3.4.1 SurfactantMixtureswithNoNetInteraction 33
3.4.2 SurfactantMixtureswithaNetInteraction 34
3.5 Surfactant–PolymerInteraction 35
3.5.1 FactorsInfluencingtheAssociationBetweenSurfactantand
Polymer 36
3.5.2 DrivingForceforSurfactant–PolymerInteraction 37
3.5.3 StructureofSurfactant–PolymerComplexes 38
3.5.4 Surfactant–HydrophobicallyModifiedPolymerInteraction 38
References 39
4 InterfacialAspectsofAgrochemicalFormulations 41
4.1 Introduction 41
4.2 EquilibriumAdsorptionofSurfactantsattheAir/Liquidand
Liquid/LiquidInterfaces 41
4.3 TheGibbsAdsorptionIsotherm 43
4.4 DynamicProcessesofAdsorption 46
4.4.1 GeneralTheoryofAdsorptionKinetics 47
4.4.2 AdsorptionKineticsfromMicellarSolutions 49
4.4.3 ExperimentalTechniquesforStudyingAdsorptionKinetics 51
4.4.3.1 TheDropVolumeTechnique 51
4.4.3.2 MaximumBubblePressureTechnique 52
4.5 AdsorptionofSurfactantsandPolymericSurfactantsatthe
Solid/LiquidInterface 55
4.6 SurfactantAdsorption 55
4.6.1 AdsorptionofIonicSurfactantsonHydrophobicSurfaces 56
4.6.2 AdsorptionofIonicSurfactantsonPolarSurfaces 59
4.6.3 AdsorptionofNonionicSurfactants 60
4.7 AdsorptionofPolymericSurfactantsattheSolid/LiquidInterface 62
4.8 ExperimentalMethodsforMeasurementofAdsorptionParameters
forPolymericSurfactants 68
4.8.1 AmountofPolymerAdsorbed,G – TheAdsorptionIsotherms 68
4.8.2 Polymer–boundFractionp 71
4.8.3 AdsorbedLayerThicknessdandSegmentDensityDistributionr(z) 72
4.8.4 HydrodynamicThicknessDetermination 72
References 74
Contents IX
5 InteractionForcesBetweenParticlesorDropletsinAgrochemical
Dispersions(SuspensionConcentratesorEmulsions,EWs)and
TheirRoleinColloidStability 77
5.1 Introduction 77
5.2 vanderWaalsAttraction 77
5.3 ElectricalDoubleLayerRepulsion 79
5.4 TotalEnergyofInteraction:Deryaguin–Landau–Verwey–Overbeek
(DLVO)Theory 81
5.5 CriteriaforStabilizationofDispersionswithDoubleLayer
Interaction 83
5.5.1 TheZetaPotential 83
5.6 StericStabilizationofDispersions 85
5.7 InteractionBetweenParticlesorDropletsContainingAdsorbed
PolymericSurfactantLayers 85
5.7.1 MixingInteraction,G 86
mix
5.7.2 ElasticInteraction,G 87
el
5.7.3 CriteriaforEffectiveStericStabilization 89
5.8 FlocculationofStericallyStabilizedDispersions 90
References 91
6 EmulsionConcentrates(EWs) 93
6.1 Introduction 93
6.2 FormationofEmulsions 94
6.3 MechanismofEmulsification 95
6.4 MethodsofEmulsification 96
6.5 RoleofSurfactantsinEmulsionFormation 97
6.5.1 RoleofSurfactantsinDropletDeformation 99
6.6 SelectionofEmulsifiers 100
6.6.1 TheHydrophilic–LipophilicBalance(HLB)Concept 100
6.6.2 ThePhaseInversionTemperature(PIT)Concept 103
6.6.3 TheCohesiveEnergyRatio(CER)ConceptforEmulsifier
Selection 105
6.6.4 TheCriticalPackingParameter(CPP)forEmulsifierSelection 107
6.6.5 EmulsionStability 108
6.7 CreamingorSedimentationofEmulsions 109
6.7.1 CreamingorSedimentationRates 110
6.7.1.1 VeryDiluteEmulsions(f50.01) 110
6.7.1.2 ModeratelyConcentratedEmulsions(0.25f50.1) 110
6.7.1.3 ConcentratedEmulsions(f40.2) 111
6.7.2 PreventionofCreamingorSedimentation 111
6.7.2.1 MatchingDensityofOilandAqueousPhases 111
6.7.2.2 ReductionofDropletSize 111
6.7.2.3 Useof‘Thickeners’ 112
6.7.2.4 ControlledFlocculation 113
6.7.2.5 DepletionFlocculation 113
X Contents
6.8 FlocculationofEmulsions 114
6.8.1 GeneralRulesforReducing(Eliminating)Flocculation 115
6.8.1.1 Charge-stabilizedEmulsions,e.g.UsingIonicSurfactants 115
6.8.1.2 StericallyStabilizedEmulsions 115
6.9 OstwaldRipening 115
6.10 CoalescenceofEmulsions 117
6.10.1 RateofCoalescence 119
6.11 PhaseInversion 119
6.12 ExperimentalMethodsforAssessmentofEmulsionStability 120
6.12.1 AssessmentofCreamingorSedimentation 121
6.12.2 AssessmentofEmulsionFlocculation 122
6.12.3 AssessmentofOstwaldRipening 123
6.12.4 AssessmentofCoalescence 123
6.12.5 AssessmentofPhaseInversion 123
References 123
7 SuspensionConcentrates(SCs) 125
7.1 Introduction 125
7.2 PreparationofSuspensionConcentratesandtheRoleof
Surfactants/DispersingAgents 126
7.3 WettingoftheAgrochemicalPowder 126
7.3.1 MeasurementofContactAnglesofLiquidsandSurfactant
SolutionsonPowders 129
7.3.2 DispersionandMilling 129
7.3.3 EffectofSurfactantAdsorption 130
7.4 ControlofthePhysicalStabilityofSuspensionConcentrates 132
7.4.1 StabilityAgainstAggregation 136
7.4.2 OstwaldRipening(CrystalGrowth) 138
7.4.3 StabilityAgainstClayingorCaking 139
7.4.4 SettlingofSuspensions 139
7.4.5 PreventionofSettlingandClaying 144
7.4.5.1 BalanceoftheDensityofDispersePhaseandMedium 144
7.4.5.2 UseofHighMolecularWeightPolymers(‘Thickeners’) 144
7.4.5.3 Useof‘Inert’FineParticles 145
7.4.5.4 UseofMixturesofPolymersandFinelyDividedSolids 146
7.4.6 ControlledFlocculation 146
7.4.7 DepletionFlocculation 146
7.5 CharacterizationofSuspensionConcentratesandAssessment
ofTheirLong-termPhysicalStability 147
7.5.1 AssessmentoftheStructureoftheSolid/LiquidInterface 148
7.5.1.1 DoubleLayerInvestigations 148
7.5.1.2 SurfactantandPolymerAdsorption 149
7.5.2 AssessmentoftheStateoftheDispersion 149
7.5.2.1 MeasurementofRateofFlocculation 149
7.5.2.2 MeasurementofIncipientFlocculation 150
Contents XI
7.5.2.3 MeasurementofCrystalGrowth(OstwaldRipening) 150
7.6 BulkPropertiesofSuspensionConcentrates 151
7.6.1 EquilibriumSedimentVolume(orHeight)andRedispersion 151
7.6.2 RheologicalMeasurements 151
7.6.2.1 AssessmentofSedimentation 152
7.6.2.2 AssessmentofFlocculation 155
7.6.3 TimeEffectsDuringFlow – Thixotropy 157
7.6.4 ConstantStress(Creep)Experiments 158
7.6.5 Dynamic(Oscillatory)Measurements 159
References 164
8 Oil-basedSuspensionConcentrates 165
8.1 Introduction 165
8.2 StabilityofSuspensionsinPolarMedia 166
8.3 StabilityofSuspensionsinNonpolarMedia 168
8.3.1 CharacterizationoftheAdsorbedPolymerLayer 169
8.4 TheoryofStericStabilization 169
8.4.1 CriteriaforEffectiveStericStabilization 172
8.5 SettlingofSuspensions 172
8.5.1 PreventionofFormationofDilatantSediments 172
8.5.2 ExamplesofSuspendingAgentsThatCanBeAppliedforPrevention
ofSettlinginNon-aqueousSuspensions 174
8.6 EmulsificationofOil-basedSuspensions 176
8.6.1 MechanismofSpontaneousEmulsificationandtheRoleofMixed
SurfactantFilm 176
8.6.2 PolymericSurfactantsforOil-basedSuspensionsandtheChoice
ofEmulsifiers 180
8.6.3 EmulsificationintoAqueousElectrolyteSolutions 180
8.7 ProperChoiceoftheAntisettlingSystem 181
8.8 RheologicalCharacteristicsoftheOil-basedSuspensions 181
References 182
9 Suspoemulsions 183
9.1 Introduction 178
9.2 SystemsInvestigated 184
9.3 ExperimentalMethods 185
9.4 ResultsandDiscussion 185
9.4.1 Creaming/SedimentationofSuspoemulsions 185
9.4.2 ReductionofInteractionsinSuspoemulsions 187
9.4.3 ReductionofHeteroflocculation 188
9.4.4 ReductionofEmulsionCoalescence 188
9.4.5 SummaryoftheCriteriaforPreparationofaStable
Suspoemulsion 189
9.4.6 PreparationofSuspoemulsionbyEmulsificationoftheOil
intotheSuspension 189