Adsorption mechanism(s) of poly(ethylene oxide) on oxide and silicate surfaces

177 Pages·1996·5.3 MB·English

by  Mathur, Sharad

ADSORPTIONMECHANISM(S)OFPOLYETHYLENEOXIDE)ON
OXIDEANDSILICATESURFACES
By
SHARADMATHUR
ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOLOFTHE
UNIVERSITYOFFLORIDAINPARTIALFULFILLMENTOFTHE
REQUIREMENTSFORTHEDEGREEOFDOCTOROFPHILOSOPHY
UNIVERSITYOFFLORIDA
1996
ACKNOWLEDGMENTS
IwouldliketoexpressmydeepestgratitudetoDr.B.M.Moudgil,mymajor
advisor,forhisinvaluableguidance,assistanceandencouragementthroughthis
investigation.
MysincerethanksgotoDr.DO.Shah,Dr.E.D.Whitney,Dr.CD.Batich,
Dr.H.El-ShallandDr,R.K.Singhforservingonmysupervisorycommittee.
Toallmyfriends-Dr.S.Behl,Dr.R.Damodaran,N.Kulkami,T.S.Prakash,
S.Zhu,R.Kalyanraman,J.AdlerandmanymoreinvolvedintheMaterialsScience
andEngineeringDepartment,Iwouldliketoexpressmythanksfortheirconstructive
suggestions and cheerful assistance during the course of this work. I also
appreciatetheexperimentalhelprenderedbyAdamBogan,JosephPuglisi,Matt
Guyot,RobertPekrulandAndrewGartskiewicz.
IwishtoacknowledgetheNSFEngineeringResearchCenterforParticle
ScienceandTechnologyattheUniversityofFloridaforprovidingfinancialsupport
(through Grant # EEC-94-02989) and a stimulating interdisciplinary research
environment.
Last,butnottheleast,IwouldliketoacknowledgemywifeAnuradhaforher
invaluableassistanceduringthepreparationofthismanuscript.
TABLEOFCONTENTS
ACKNOWLEDGMENTS "
ABSTRACT xii
CHAPTERS
1 INTRODUCTION 1
AdsorptionofPolymersatSolid/LiquidInterface 1
PolymerAdsorption 1
Applications 3
PolymerAdsorptionMechanisms 3
2 BACKGROUND 9
Introduction 9
SourceofIsolatedHydroxylsonDolomite 10
AdsorptionMechanismofPEOonDolomiteSamples 10
DeficienciesintheProposedAdsorptionMechanismofPEO 10
ScopeofthePresentStudy 13
3 EXPERIMENTAL 14
Materials 14
OxideSamples 14
SilicateSamples I4
Polymers 19
OtherChemicals 19
Methods 19
ChemicalComposition 19
ParticleCharacterization 21
PEOCharacterization 23
SurfaceChemicalCharacterization 26
AFMStudies 27
FlocculationStudies 28
AdsorptionStudies 30
4 FLOCCULATIONANDADSORPTIONSTUDIESONOXIDES 33
Introduction 33
in
FlocculationStudies 33
EffectofPolymerMolecularWeight 33
EffectofDosage 33
EffectofFloeDetectionTechnique 36
ElectrokineticStudies 38
EffectofpHonFlocculationofOxideswithPEO 38
AdsorptionStudies 45
AdsorptionKineticsofPEOonOxides 45
AdsorptionIsothermsofPEOonOxides 45
AdsorptionMechanismofPEO 52
EffectofNegativelyChargedSurface 53
EffectofHydratedCounter-Ions 53
AFMStudies 54
RoleofSpecificSurfaceBindingSitesinPEO
AdsorptiononSilica 62
ROLEOFSURFACEACIDITYOFOXIDESINPEOADSORPTION .. 63
Introduction 63
AccessibilityofSurfaceSitestoPEOMolecules 63
ConcentrationofSurfaceHydroxyls 64
HeatofWettingofOxides 66
NatureofSurfaceHydroxyls 66
PointofZeroChargeofOxides 66
CorrelationbetweenHeatofWettingandpzcofOxides 68
RoleofBronstedAcidityinPEOAdsorption 70
ARwdeisltaohtripPotEniOoBnetanwdeeFnloTcycpuleatoifoOnxBiedheavainodriotsfPMooin0t3OafnZdeVro2C5harge . 7713
RoleofLewisAcidSites 82
Oxide/PEO/CCI4system 84
Hematite/Starch/WaterSystem 84
CHARACTERIZATIONOFPEOBINDINGSITES
ONOXIDESURFACES 86
Introduction 86
SurfaceHydroxylsonOxides 88
IsolatedHydroxylsandPEOAdsorption 92
EffectofHeatPretreatment 94
AdsorptionofPEOonHeatTreatedSamples 97
CharacterizationofSurfaceAcidityofOxides 101
DRIFTSpectraofAdsorbedPyridineonOxides 101
AcidityofSilanolGroups .104
IV
SurfaceAnalysisofSilicaandAdsorptionofPEO 104
SpecificityofHydrogen-BondingofIsolatedSilanols 104
EffectofpH 107
7 ADSORPTIONANDFLOCCULATIONBEHAVIOROFSILICATES
WITHPEO 109
Introduction 109
AdsorptionandFlocculationStudies 109
FlocculationofSilicates 109
EffectofFlocculantDosage 110
AdsorptionStudiesonSilicates 113
AFMStudiesofAdsorbedMoleculesonTremoliteandAugite 122
SurfaceCharacterizationofSilicateMinerals 135
CorrelationbetweenIsolatedHydroxylsandAdsorption 138
AdsorptionMechanism(s)ofPEOonSilicates 140
8 CONCLUSIONSANDFUTUREWORK 146
Summary 146
SuggestionsforFutureWork 150
REFERENCES 152
BIOGRAPHICALSKETCH 161
.
LISTOFFIGURES
Figure Page
1.1. Conformationoftheadsorbedpolymermolecule 2
1.2. Schematicillustratingstericstabilizationofparticles 4
1.3. Schematicofbridgingflocculationofparticles 5
1.4. Schematicillustratingtheselectiveflocculationprocess 6
3.1. Crystalstructuresofsilicatesamples 18
3.2. SizedistributionofPEOsamples 25
3.3. CalibrationcurvesforanalysisofPEOinsolution 32
4.1 Flocculationbehaviorofoxidesamplesasafunctionof
molecularweightofPEO(dosage0.5mg/g;pH=9.5) 34
4.2. dFlooscacguleatoifoPnEbOehaofviMorWof8,o0x0id0e,0s0a0maptlepsHa9s.5afunctionof 35
4.3. BedvolumeofsilicasedimentasafunctionofPEOdosage
(MW=5,000,000)atpH9.5 37
4.4. ElectrokineticbehaviorofoxidesasafunctionofpH
(I=0.03kmol/m3) 39
4.5. (FlPoEcOculMatWion=b5e,h0a00v,i0o0r0o;fdsiolsicaagsea=mp0l.e5smga/sga)functionofpH 41
4.6. FlocculationbehaviorofsilicaAasafunctionofPEO
molecularweightatdifferentpH(PEOdosage=0.5mg/g) 43
4.7. ElectrokineticbehaviorofsilicaAwithandwithoutPEO
(1=0.03kmol/m3) 44
4.8. (EqPuEiOlibMriWum=ad8s,o0r0p0t,i0o0n0;tipmHe=for9.P5)EOonoxides 46
vi
.
4.9. A(dPsEoOrpMtiWon=is5o,t0h0e0r,m0s00f)oroxide-PEOsystematpH9.5 47
4.10 A(dPsEoOrpMtiWon=is5o,t0h0e0r,m0s00f)oroxide-PEOsystematpH3.0 48
4.11 AdsorptionisothermofPEO(MW=8,000,000)onsilicaAatpH9.5. .51
4.12. AFMimageofthebaresilicasurface 55
4.13. AFMTappingModetopographicimageofadsorbedPEO
(MW=5,000,000atpH3.0) 56
4.14. AFMTappingModetopographicimageofadsorbedPEO
atpH9.5after1 hourofdesorption 58
4.15. AFMTappingModetopographicimageofadsorbedPEO
atpH9.5after2hourofdesorption 59
4.16. EffectofpHoninterparticleforcesbetweensilicasphere
andaflatplatewithandwithoutPEO(MW=5,000,000) 61
5.1. SchematicofBronstedacidsites 69
5.2. Heatofwettingofoxidesasafunctionoftheirpointofzerocharge.
(After[Hea65]) 70
5.3. fEulneccttirooknionfetpicHbehaviorofMo03andV2 5suspensionsas 75
5.4. A(dPsEoOrpMtiWon=is5o,t0h0e0r,m0s00o;fpPHE=O3o.0n)Mo03andV2 5suspensions 76
5.5. SaturationadsorptiondensityofPEO(MW=5,000,000)atpH3.0
asafunctionofthepointofzerochargeofoxides 77
5.6. FlocculationbehaviorofMo03andV2 5asafunctionof
molecularweight(dosage=0.5mg/gatpH3.0) 79
5.7. FlocculationofMo03andV2 5asafunctionofPEOdosage(pH3.0). 80
5.8. SchematicshowingaLewisacidsite 84
6.1 Schematicshowingsurfacehydroxylationonvariousfacesofanatase. 88
6.2. DRIFTspectraofoxidesinthehydroxylregion 90
vii
.
6.3. DRIFTspectraofsilicaBandhematiteinthehydroxylregion 91
6.4. DRIFTspectraofheattreatedsilicasamples 96
6.5. Schematicofi)amorphoussilicasurfaceshowingtheringstructure
andii)influenceofsurfacecurvatureonH-bonding 97
6.6. DRIFTspectrashowingeffectofheattreatmentonthesurface
hydroxylationofaluminaA 99
6.7. A(dPsEoOrpMtiWon=i5s,o0t0h0e,r0m0s0)ofPEOforheattreatedoxidesatpH9.5 100
6.8. DRIFTspectraofpyridinetreatedMo03,V2 5andSi02samples. ... 104
6.9. Plotofthechangeinfrequencyofisolatedsilanolsagainstthe
specificheatofadsorptionforseveralvaporsadsorbedonsilica
surface(dataafter[Kis65]andAnd[65a] 107
7.1 FlocculationofsilicatesasafunctionofmolecularweightofPEO
(pH=9.5;dosage=1mg/g) 110
7.2. FlocculationbehaviorofaugiteasafunctionofPEOdosage
atpH9.5 113
7.3. FlocculationbehavioroftremoliteasfunctionofPEOdosage
atpH=9.5 115
7.4. KineticsofPEOadsorptionontremoliteandaugite 116
7.5. A(dPsEoOrpMtiWon=is5o,t0h0e0r,m0s00o)fPEOonchainandorthosilicatesatpH9.5 117
7.6. A(dPsEoOrpMtiWon=is5o,t0h0e0r,m0s00o)fPEOonclaysatpH9.5 118
7.7. AFMimageofbaretremolitesurface 124
7.8. AFMimageofadsorbedPEOontremolite 125
7.9. AFMFrictionimageofadsorbedPEOontremolite 126
7.10. HistogramofparkingareaofPEOmoleculesontremolite 127
7.11 AFMimageofbareaugitesurface 131
VIII
7.12. AFMimageofadsorbedPEOonaugite 132
7.13. AFMFrictionimageofadsorbedPEOonaugite 133
7.14. HistogramofparkingareaofPEOmoleculesonaugite 134
7.15. DRIFTspectraofchainandlayeredsilicatesinthehydroxylregion... 137
7.16. DRIFTspectraoforthosilicatemineralsinthehydroxylregion 138
7.17. AdsorptionofPEOonclaysbyinteractionoftheetheroxygenofPEO
withthehydrationshelloftheexchangeableion(Bronstedacidsite). 143
IX
LISTOFTABLES
Table Page
2.1. Correlationbetweentheintensityoftheisolatedhydroxylgroupson
dolomitesampleswithflocculationandthesaturationadsorption
densityofPEOof5,000,000MW[Beh93a] 11
3.1. Oxidesamplesandtheirsources 15
3.2. StructuralUnitsObservedinCrystallineSilicates(After[Kin76]) 16
3.3. Silicatesamplesselectedandtheiridealizedchemicalcomposition. ..17
3.4. CharacteristicsofthePolymersusedinthisstudy 20
3.5. PhysicalCharacteristicsoftheoxidesamples 22
3.6. Physicalcharacteristicsofthesilicatesamples 24
3.7. Dimensionsoftheflocculationcell 29
4.1. IsoelectricPointofOxidesdeterminedbyElectrokineticStudies 40
4.2. SaturationadsorptiondensityofPEO(MW=5,000,000)onoxide
samplesatdifferentpH 49
5.1. Concentrationofsurfacehydroxylgroups[And82] 65
5.2. HeatofWettingvaluesforoxidesinwater[Che59;Hea65] 67
5.3. Probablerangesofpzcofdifferenttypesofoxides[Par65] 73
5.4. DissolutionbehaviorofMo03and V2 5powdersandthe
adsorptionofdissolvedionsonotheroxides 82
6.1. aSdusrofrapcteiohnyddreonxsyiltsyoonfPdiEffOerentoxidesandthesaturation 94