edited by · 7 dielectric relaxation spectroscopy for polymer nanocomposites 167 chetan chanmal and...
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Polymer Nano-, Micro- & Macrocomposite Series
Mittal, V. (ed.)
Surface Modification of Nanotube FillersSeries: Polymer Nano-, Micro- and Macrocomposites (Volume 1)
2011
ISBN: 978-3-527-32878-9
Mittal, V. (ed.)
In-situ Synthesis of Polymer NanocompositesSeries: Polymer Nano-, Micro- and Macrocomposites (Volume 2)
2012
ISBN: 978-3-527-32879-6
Mittal, V. (ed.)
Modeling and Prediction of Polymer Nanocomposite PropertiesSeries: Polymer Nano-, Micro- and Macrocomposites (Volume 4)
2013
ISBN: 978-3-527-33150-5
Related Titles
Mittal, V. (ed.)
Polymer Nanotube NanocompositesSynthesis, Properties, and Applications
2010
ISBN: 978-0-470-62592-7
Mittal, V. (ed.)
Miniemulsion Polymerization Technology
2010
ISBN: 978-0-470-62596-5
Mittal, Vikas (ed.)
Optimization of Polymer Nanocomposite Properties
2010
ISBN: 978-3-527-32521-4
Thomas, S., Joseph, K., Malhotra, S. K., Goda, K., Sreekala, M. S. (eds.)
Polymer CompositesVolume 1
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ISBN: 978-3-527-32624-2
Cosnier, S., Karyakin, A. (eds.)
ElectropolymerizationConcepts, Materials and Applications
2010
ISBN: 978-3-527-32414-9
Leclerc, M., Morin, J.-F. (eds.)
Design and Synthesis of Conjugated Polymers
2010
ISBN: 978-3-527-32474-3
The Editor
Dr. Vikas MittalThe Petroleum InstituteChemical Engineering DepartmentRoom 2204, Bu Hasa BuildingAbu DhabiUAE
All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.
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©2012 Wiley-VCH Verlag & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany
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Print ISBN: 978-3-527-33148-2ePDF ISBN: 978-3-527-65453-6ePub ISBN: 978-3-527-65452-9mobi ISBN: 978-3-527-65451-2oBook ISBN: 978-3-527-65450-5ISSN: 978-3-527-64011-9
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V
Contents
Preface XIII ListofContributors XV
1 CharacterizationofNanocompositeMaterials:AnOverview 1VikasMittal
1.1 Introduction 11.2 CharacterizationofMorphologyandProperties 21.3 ExamplesofCharacterizationTechniques 5
References 12
2 ThermalCharacterizationofFillersandPolymerNanocomposites 13VikasMittal
2.1 Introduction 132.2 TGAofFillers 132.2.1 QuantificationoftheExtentofSurfaceModification 142.2.2 CleanlinessoftheFillerSurface 142.2.3 ComparingtheStabilityofDifferentFillers 152.2.4 DynamicTGAAnalysisoftheFillers 182.2.5 CharacterizationoftheSurfaceReactions 192.2.6 DifferentMeasurementEnvironments 192.2.7 CorrelationofOrganicMatterwithBasalSpacing 222.3 TGAofPolymerNanocomposites 232.3.1 EffectofFillerConcentration 232.3.2 EffectofCompatibilizer 252.4 DSCofFillers 252.4.1 ThermalTransitionsintheModifiedFillers 262.5 DSCofComposites 262.5.1 TransitionsinComposites 262.5.2 OptimizationofCuringConditions 29
References 32
VI Contents
3 Flame-RetardancyCharacterizationofPolymerNanocomposites 33JosephH.Koo,SiChonLao,andJasonC.Lee
3.1 Introduction 333.2 TypesofFlame-RetardantNanoadditives 333.2.1 One-DimensionalNanomaterials 343.2.1.1 MontmorilloniteClay 343.2.1.2 NanographenePlatelets 353.2.2 Two-DimensionalNanomaterials 363.2.2.1 CarbonNanofibers 363.2.2.2 CarbonNanotubes 363.2.2.3 HalloysiteNanotubes 393.2.3 Three-DimensionalNanomaterials 403.2.3.1 Nanosilica 403.2.3.2 Nanoalumina 403.2.3.3 NanomagnesiumHydroxide 403.2.3.4 PolyhedralOligomericSilsequioxanes 413.3 Thermal,Flammability,andSmokeCharacterizationTechniques 423.3.1 IntroductiontoTestMethods 423.3.2 ThermogravimetricAnalysis(TGA) 433.3.3 TheUL94VerticalFlameTest 433.3.4 OxygenIndex(LimitingOxygenIndex)(ASTMD2863-97) 443.3.5 ConeCalorimeter(ASTME1354) 443.3.6 MicroscaleCombustionCalorimeter(ASTMD7309) 453.3.7 SteinerTunnelTest(ASTME84) 453.4 ThermalandFlameRetardancyofPolymerNanocomposites 463.4.1 One-DimensionalNanomaterial-BasedNanocomposites 463.4.1.1 Polymer–ClayNanocomposites 463.4.1.2 Polymer–GrapheneNanocomposites 523.4.2 Two-DimensionalNanomaterial-BasedNanocomposites 543.4.2.1 PolymerCarbonNanofiberNanocomposites 543.4.2.2 PolymerCarbonNanotubeNanocomposites 543.4.2.3 PolymerHalloysiteNanotubeNanocomposites 553.4.3 Three-DimensionalNanomaterial-BasedNanocomposites 573.4.3.1 PolymerNanosilicaNanocomposites 573.4.3.2 PolymerNanoaluminaNanocomposites 573.4.3.3 PolymerNanomagnesiumHydroxideNanocomposites 583.4.3.4 PolymerPOSSNanocomposites 603.4.4 MulticomponentFRSystems:PolymerNanocompositesCombined
withAdditionalMaterials 623.4.4.1 Polymer–ClaywithConventionalFRAdditiveNanocomposites 623.4.4.2 Polymer–CarbonNanotubeswithConventionalFRAdditive
Nanocomposites 633.4.4.3 Polymer–Clayand–CarbonNanotubeswithConventionalFRAdditive
Nanocomposites 643.5 FlameRetardantMechanismsofPolymerNanocomposites 66
Contents VII
3.6 ConcludingRemarksandTrendsofPolymerNanocomposites 68Acknowledgments 69References 69
4 PVTCharacterizationofPolymericNanocomposites 75LeszekA.Utracki
4.1 Introduction 754.2 ComponentsofPolymericNanocomposites 764.2.1 Size,SizeDistribution,andShapeoftheClayPlatelets 774.2.2 ChemicalCompositionofClays 784.2.3 Impurities 794.3 Pressure–Volume–Temperature(PVT)Measurements 794.3.1 Transitions 794.3.2 DeterminationofPVT 804.3.3 EffectsofClay,Intercalant,andCompatibilizer 824.4 Derivatives,Compressibility,andThermalExpansionCoefficient 834.4.1 InterpolatingtheData 834.4.2 ComputationoftheThermalExpansionandCompressibility
Coefficients,αandκ 844.4.3 PolymerαandκfromPVT 844.4.4 EffectofClayonαandκinPS-BasedPNC 864.4.5 EffectofClayonαandκinPA-6BasedPNC 874.5 ThermodynamicTheories 894.5.1 Simha–SomcynskyCell-HoleTheory 904.5.2 Simha–SomcynskyeosforMulticomponentSystems 934.5.3 TheVitreousRegion 974.5.4 EquationofStateforSemicrystallinePNC 984.6 ThermodynamicInteractionCoefficients 1004.7 TheoreticalPredictions 1054.8 SummaryandConclusions 1064.8.1 CharacterizationofClays 1074.8.2 PVTMeasurements 1084.8.3 DerivativeProperties 1084.8.4 ThermodynamicTheories 1084.8.5 InteractionParameters 1094.8.6 TheoreticalPredictions 109
References 109
5 FollowingtheNanocompositesSynthesisbyRamanSpectroscopyandX-RayPhotoelectronSpectroscopy(XPS) 115SorinaAlexandraGareaandHoriaIovu
5.1 NanocompositesBasedonPOSSandPolymerMatrix 1155.1.1 Introduction 1155.1.2 RamanSpectroscopyAppliedforFollowingtheSynthesisof
NanocompositesBasedonPolymerMatrixandPOSS 116
VIII Contents
5.1.3 XPSAppliedforCharacterizationofPolymer-POSSNanocomposites 126
5.1.3.1 AnalysisofFunctionalizedPOSSMolecules 1265.1.3.2 CharacterizationofNanocompositeMaterials 1285.1.4 Conclusions 1285.2 RamanandXPSAppliedinSynthesisofNanocompositesBasedon
CarbonNanotubesandPolymers 1295.2.1 Introduction 1295.2.2 X-RayPhotoelectronSpectroscopy(XPS)UsedtoMonitorizethe
SynthesisofPolymer-CNT-BasedNanocomposites 1305.2.2.1 CNTFunctionalizationwithCarboxylicGroups 1315.2.2.2 CNTFunctionalizationwithAmines 1315.2.2.3 CNTFunctionalizationwithBioconjugatedSystemsBasedon
DendriticPolymersandAntitumoralDrug 1335.2.3 Polymer-CNT-BasedNanocompositesSynthesisFollowedbyRaman
Spectroscopy 1355.2.4 Conclusions 137
Acknowledgments 138References 138
6 TribologicalCharacterizationofPolymerNanocomposites 143MarkusEnglertandAloisK.Schlarb
6.1 Introduction 1436.2 TribologicalFundamentals 1446.2.1 TribologicalSystem 1456.2.2 WearMechanisms 1466.2.3 TransferFilmFormation 1486.2.4 TemperatureIncrease 1486.3 WearExperiments 1496.3.1 SelectedWearModels 1506.3.2 CharacteristicValuesofTribologicalSystems 1506.3.2.1 WearRate 1526.4 SelectionCriteria 1526.5 DesignofPolymerNanocompositesandMultiscale
Composites 1536.6 SelectedExperimentalResults 1536.6.1 ParticulateFillers 1536.6.2 ShortFibers 1556.6.3 CombinationofFillers 1566.6.3.1 InternalLubricantsandShortCarbonFibers 1566.6.3.2 ShortCarbonFibersandNanoparticles 1576.6.4 WearMechanisms 1616.6.4.1 BallBearing(“Rolling”)EffectonaSubmicroScale 1616.6.5 Summary 163
References 165
Contents IX
7 DielectricRelaxationSpectroscopyforPolymerNanocomposites 167ChetanChanmalandJyotiJog
7.1 Introduction 1677.2 TheoryofDielectricRelaxationSpectroscopy 1687.2.1 DielectricRelaxationsinPolymerNanocomposites 1687.2.2 FittingtoExperimentalData 1697.2.3 ActivationEnergyoftheRelaxationProcess 1697.2.4 ModulusFormalism 1707.3 PVDF/ClayNanocomposites 1717.3.1 FrequencyDependenceofDielectricPermittivity 1717.3.2 Vo–ShiModelFittingtoDielectricPermittivity 1727.3.3 RoleofInterface 1737.3.4 FrequencyDependenceofDielectricRelaxationSpectra 1737.4 PVDF/BaTiO3Nanocomposites 1757.4.1 FrequencyDependenceofDielectricRelaxationSpectra 1757.4.2 ElectricModulusPresentationofDielectricRelaxationSpectra 1767.4.3 ActivationEnergyofCrystallineandMWSRelaxation
Processes 1777.5 PVDF/Fe3O4Nanocomposites 1777.5.1 Low-TemperatureDielectricRelaxationSpectra 1787.5.2 ActivationEnergyofGlassTransitionRelaxation 1807.5.3 NormalizedSpectraofDielectricRelaxation 1807.6 ComparativeAnalysisofPVDFNanocomposites 1817.7 Conclusions 182
Acknowledgment 182Nomenclature 182References 183
8 AFMCharacterizationofPolymerNanocomposites 185KenNakajima,DongWang,andToshioNishi
8.1 AtomicForceMicroscope(AFM) 1858.1.1 PrincipleofAFM 1858.1.2 PrincipleofTappingModeAFM 1888.1.3 PhaseandEnergyDissipation 1918.2 ElasticityMeasuredbyAFM 1938.2.1 SampleDeformation 1938.2.2 ContactMechanics 1948.2.3 Sneddon’sElasticContact 1948.2.4 NanopalpationRealizedbyAFM 1978.2.5 AdhesiveContact 1988.2.6 NanomechanicalMapping 2008.3 ExampleStudies 2018.3.1 CarbonNanotubes-ReinforcedElastomerNanocomposites 2018.3.2 InvestigationoftheReactivePolymer–PolymerInterface 2078.3.3 NanomechanicalPropertiesofBlockCopolymers 213
X Contents
8.4 Conclusion 225References 225
9 ElectronParamagneticResonanceandSolid-StateNMRStudiesoftheSurfactantInterphaseinPolymer–ClayNanocomposites 229GunnarJeschke
9.1 Introduction 2299.2 NMR,EPR,andSpinLabelingTechniques 2309.2.1 Solid-StateNMRSpectroscopy 2309.2.2 EPRSpectroscopy 2319.2.3 SpinLabelEPR 2329.2.4 SpinLabelingoftheSurfactantInterphase 2369.3 CharacterizationofOrganicallyModifiedLayeredSilicates 2379.3.1 HeterogeneityofOrganoclays 2379.3.2 HeterogeneityandPositionDependenceofSurfactant
Dynamics 2389.3.3 FurtherFeaturesofSurfactantDynamics 2399.3.4 StructuralAspectsoftheSurfactantLayer 2409.4 CharacterizationofNanocomposites 2429.4.1 IntercalatedNanocompositesandNonintercalatedComposites 2429.4.2 InfluenceofthePolymeronSurfactantDynamics 2439.4.3 InfluenceofthePolymeronSurfactantLayerStructure 2449.5 Conclusion 247
Acknowledgments 248References 248
10 CharacterizationofRheologicalPropertiesofPolymerNanocomposites 251MoSongandJieJin
10.1 Introduction 25110.2 FundamentalRheologicalTheoryforStudyingPolymer
Nanocomposites 25210.3 CharacterizationofRheologicalPropertiesofPolymer
Nanocomposites 25710.4 Conclusions 279
References 280
11 SegmentalDynamicsofPolymersinPolymer/ClayNanocompositesStudiedbySpin-LabelingESR 283YoheiMiwa,ShulamithSchlick,andAndrewR.Drews
11.1 Introduction 28311.2 SpinLabeling:BasicPrinciples 28411.2.1 ESRSpectraofNitroxideRadicals 28411.2.2 LineShapeAnalysisofNitroxideRadicals 28511.3 ExfoliatedPoly(methylacrylate)(PMA)/ClayNanocomposites 286
Contents XI
11.3.1 PreparationofExfoliatedNanocompositesintheAbsenceofSurfactants 286
11.3.2 StructureofExfoliatedNanocomposites 28711.3.3 SegmentalDynamicsofPMAinNanocomposites 28811.3.3.1 TheGlassTransitionTemperature 28811.3.3.2 RestrictedMolecularMotionatthePMA/ClayInterface 28911.3.3.3 ThicknessoftheInterfacialRegion 29111.4 IntercalatedPoly(ethyleneoxide)(PEO)/ClayNanocomposites 29311.4.1 PreparationofIntercalatedPEO/ClayNanocomposites 29311.4.2 StructureofIntercalatedNanocomposites 29411.4.2.1 IntercalationofPEOinClayGalleriesofThickness<1nm 29411.4.2.2 InhibitedCrystallization 29511.4.2.3 DisappearanceoftheGlassTransition 29511.4.2.4 HinderedHydrogenBonding 29611.4.3 SegmentalDynamicsofPEOinClayGalleries 29811.4.3.1 SimulationofESRSpectraandDeterminationofDynamic
Parameters 29811.4.3.2 EffectofGalleryThicknessontheSegmentalMobilityof
IntercalatedPEO 30011.4.3.3 EffectofMolecularWeightontheSegmentalMobilityof
IntercalatedPEO 30011.5 Conclusions 300
Acknowledgments 301References 301
12 CharacterizationofPolymerNanocompositeColloidsbySedimentationAnalysis 303VikasMittal
12.1 Introduction 30312.2 MaterialsandExperimentalMethods 30512.2.1 HybridColloidDispersions 30512.2.2 TurbidityandInterferenceAUC 30512.2.3 StaticDensityGradients 30612.2.4 PreparativeUltracentrifugation 30612.3 ResultsandDiscussion 30712.4 Conclusions 319
Acknowledgments 320References 320
13 BiodegradabilityCharacterizationofPolymerNanocomposites 323KatherineM.Dean,ParveenSangwan,CameronWay,andMelissaA.L.Nikolic
13.1 Introduction 32313.2 MethodsofMeasuringBiodegradation 32313.2.1 AnalyticalTechniques 324
XII Contents
13.2.1.1 Morphological 32413.2.1.2 Microscopic 32413.2.1.3 Gravimetric 32413.2.1.4 PhysicalandThermal 32413.2.1.5 Spectroscopic 32413.2.1.6 Chromatographic 32513.2.1.7 Respirometry 32513.2.2 OxygenDemand 32713.2.3 MicrobiologicalTechniques 32813.2.3.1 DirectCellCount 32813.2.3.2 Clear-Zone 32813.2.3.3 PourPlate/StreakPlate 32913.2.3.4 Turbidity 32913.2.4 EnzymaticTechniques 32913.2.5 MolecularTechniques 32913.3 StandardsforBiodegradation 33113.4 BiodegradableNanocomposites 33113.4.1 PLANanocomposites 33313.5 StarchNanocomposites 33613.6 PCLNanocomposites 33713.7 PHA/PHBNanocomposites 33913.8 NanocompositesofPetrochemical-BasedPolymer 34213.9 Conclusions 343
References 343
Index 347
XIII
Preface
Polymer layered silicate nanocomposites are relatively a new class of nanoscale materials, in which at least one dimension of the filler phase is smaller than 100 nm. They offer an opportunity to explore new behaviors and functionalities beyond that of conventional materials. A large number of advancements have been made in the techniques to modify the filler surface as well as to synthesize the polymer nanocomposites. Such advances need to be supplemented with robust characterization of the resulting composite morphology and properties to gain insights into the various factors affecting the nanocomposite microstructure and properties to be able to design them according to the need. The book summarizes a large number of characterization techniques that have been employed to analyze various aspects of polymer nanocomposites. The aim of the book is also to estab-lish right practices for characterizing the nanocomposite materials with any spe-cific technique.
Chapter 1 provides an overview of the most common characterization tech-niques for the polymer nanocomposites including thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and permeation resistance. Chapter 2 details the thermal characterization of the modified fillers as well as nanocomposites. Correlations of the thermal information with other techniques like X-ray diffrac-tion have also been presented. Chapter 3 focuses on the flame retardancy charac-terization of nanocomposites. Various flame retardants as well as flammability tests have been described in light of a large number of polymer clay nanocompos-ites. PVT characterization of the polymer nanocomposites is described in Chapter 4. The chapter deals with characterization of clays, PVT measurements, derivative properties, thermodynamic theories, interaction parameters, and theoretical predictions. Chapter 5 reports on the nanocomposites synthesis analysis by Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Both POSS and nanotube-based polymer nanocomposites are reviewed. Tribological characteriza-tion of the nanocomposites is described in Chapter 6. First, the basics of tribology are discussed, followed by the description of possibilities in order to develop tri-bologically optimized nanocomposites. Afterward their characterization by special tribological methods is focused as well as selected results in respect of the tribo-logical properties of nanocomposites. Chapter 7 reports on the use of dielectric
XIV Preface
relaxation spectroscopy for polymer nanocomposites based on poly(vinylidene fluoride) (PVDF). A variety of nanofillers such as clay with platelet structure and functional nanoparticles like BaTiO3 and Fe3O4 is explored. Chapter 8 is devoted to describing how atomic force microscope (AFM) is used to characterize polymer nanocomposites. In particular, a newly developed AFM-based technique is intro-duced to obtain Young’s modulus map for various types of polymeric materials. Electron paramagnetic resonance and solid-state NMR studies of the surfactant interphase in polymer–clay nanocomposites are described in Chapter 9. The infor-mation from NMR and EPR on structure and dynamics of surfactant molecules in OMLS is used to provide a solid foundation for discussion of the more complex interphase behavior in the nanocomposites. Chapter 10 focuses on the rheological characterization of polymer nanocomposites. Basic rheological theories are intro-duced and a brief review of the current status of the understanding of rheological properties of polymer nanocomposites is provided. Chapter 11 reports on the segmental dynamics of polymers in polymer clay nanocomposites studied by spin-labeling electron spin resonance (ESR). This is a powerful technique for discerning properties of specific labeled regions or components in complex systems and can provide information on the dynamics on time scales in the range 10−11–10−7 s.
Chapter 12 reports the characterization of the polymer inorganic hybrid colloidal particles by the use of analytical and preparative ultracentrifugation. Biodegrada-bility characterization of nanocomposites is focused on in Chapter 13. The meth-odologies used to measure and understand biodegradation of nanocomposites are discussed. The standards associated with methods are also described followed by a discussion on the biodegradation of a number of nanocomposites types.
I am grateful to Wiley VCH for their kind acceptance to publish the book. I dedicate this book to my mother for being a constant source of inspiration. I express heartfelt thanks to my wife Preeti for her continuous help in co-editing the book as well as for her ideas to improve the manuscript.
Vikas Mittal
XV
ListofContributors
Chetan ChanmalNational Chemical LaboratoryPolymer Science and Engineering DivisionDr. Homi Bhabha RoadPashanPune, Maharashtra 411008India
Katherine M. DeanCSIRO Materials Science and EngineeringGate 5 Normanby RdClayton, Vic. 3168Australia
Andrew R. DrewsFord Motor CompanyFord Research and Advanced EngineeringMD 3179P.O. Box 2053Dearborn, MI 48121USA
Markus EnglertUniversity of KaiserslauternGottlieb Daimler StrasseGebäude 4467663 KaiserslauternGermany
Sorina Alexandra GareaUniversity Politehnica of BucharestAdvanced Polymer Materials Group149 Calea Victoriei010072 BucharestRomania
Horia IovuUniversity Politehnica of BucharestAdvanced Polymer Materials Group149 Calea Victoriei010072 BucharestRomania
Gunnar JeschkeLab. Phys. Chem.ETH ZürichWolfgang-Pauli-Strasse 108093 ZürichSwitzerland
Jie JinLoughborough UniversityDepartment of MaterialsAshby RoadLoughborough LE11 3TUUK
XVI ListofContributors
Jyoti JogNational Chemical LaboratoryPolymer Science and Engineering DivisionDr. Homi Bhabha RoadPashanPune, Maharashtra 411008India
Joseph H. KooThe University of Texas at AustinDepartment of Mechanical EngineeringTexas Materials InstituteCenter for Nano and Molecular Science and Technology1 University StationC2200Austin, TX 78712-0292USA
Si Chon LaoThe University of Texas at AustinDepartment of Mechanical EngineeringTexas Materials InstituteCenter for Nano and Molecular Science and Technology1 University StationC2200Austin, TX 78712-0292USA
Jason C. LeeInstitute for Soldier NanotechnologiesDepartment of Chemical EngineeringMassachusetts Institute of Technology77 Massachusetts Ave.Cambridge, MA 02139USA
Vikas MittalThe Petroleum InstituteChemical Engineering DepartmentRoom 2204, Bu Hasa BuildingAbu DhabiUnited Arab Emirates
Yohei MiwaUniversity of Detroit MercyDepartment of Chemistry and Biochemistry4001 West McNichols RoadDetroit, MI 48221-3038USA
Ken NakajimaWPI-Advanced Institute forMaterials Research (WPI-AIMR)Tohoku University2-1-1 Katahira, Aoba-ku, SendaiMiyagi 980-8577Japan
Melissa A.L. NikolicCSIRO Materials Science and EngineeringGate 5 Normanby RdClayton, Vic. 3168Australia
Toshio NishiWPI-Advanced Institute forMaterials Research (WPI-AIMR)Tohoku University2-1-1 Katahira, Aoba-ku, SendaiMiyagi 980-8577Japan
ListofContributors XVII
Parveen SangwanCSIRO Materials Science and EngineeringGate 5 Normanby RdClayton, Vic. 3168Australia
Alois K. SchlarbUniversity of KaiserslauternGottlieb Daimler StrasseGebäude 4467663 KaiserslauternGermany
Shulamith SchlickUniversity of Detroit MercyDepartment of Chemistry and Biochemistry4001 West McNichols RoadDetroit, MI 48221-3038USA
Mo SongLoughborough UniversityDepartment of MaterialsAshby RoadLoughborough LE11 3TUUK
Leszek A. UtrackiNational Research Council CanadaIndustrial Materials Institute75 de MortagneBoucherville, QCCanada J4B 6Y4
Dong WangWPI-Advanced Institute forMaterials Research (WPI-AIMR)Tohoku University2-1-1 Katahira, Aoba-ku, SendaiMiyagi 980-8577Japan
Cameron WayCSIRO Materials Science and EngineeringGate 5 Normanby RdClayton, Vic. 3168Australia
1
1
Characterization Techniques for Polymer Nanocomposites, First Edition. Edited by Vikas Mittal.© 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.
CharacterizationofNanocompositeMaterials:AnOverviewVikasMittal
1.1Introduction
Polymer layered silicate nanocomposites are relatively new class of nanoscale materials, in which at least one dimension of the filler phase is smaller than 100 nm [1–9]. They offer an opportunity to explore new behaviors and functionali-ties beyond that of conventional materials. Owing to nanometer thick platelets in layered silicates, incorporation of such fillers strongly influences the properties of the composites at very low volume fractions because of much smaller interparticle distances and the conversion of a large fraction of the polymer matrix near their surfaces into an interphase of synergistically improved properties. As a result, the desired properties are usually reached at low filler volume fraction, which allows the nanocomposites to retain the macroscopic homogeneity and low density of the polymer.
Montmorillonite has been a layered silicate of choice for most of the studies on polymer nanocomposites. Montmorillonite is an expandable dioctahedral smectite belonging to the family of the 2 : 1 phyllosilicates [10, 11] with a general formula of Mx(Al4−xMgx)Si8O20(OH)4. The particles in montmorillonites consist of stacks of 1 nm thick aluminosilicate layers (or platelets) held electrostatically with each other with a regular gap in between (interlayer). Each layer consists of a central Al-octahedral sheet fused to two tetrahedral silicon sheets. Isomorphic substitutions of aluminum by magnesium in the octahedral sheet generate negative charges, which are compensated for by alkaline-earth or hydrated alkali-metal cations. Based on the extent of the substitutions in the silicate crystals, a term called layer charge density is defined. Montmorillonites have a mean layer charge density of 0.25–0.5 equiv. mol−1. The layer charge is also not constant and can vary from layer to layer; therefore, it should be considered more of an average value. The electro-static and van der Waals forces holding the layers together are relatively weak in smectites and the interlayer distance varies depending on the radius of the cation present and its degree of hydration. As a result, the stacks swell in water and the
2 1 CharacterizationofNanocompositeMaterials:AnOverview
1 nm thick layers can be easily exfoliated by shearing, giving platelets with high aspect ratio. This thus helps to easily exchange their inorganic cations with organic ions (e.g., alkylammonium) to give organically modified montmorillonite (OMMT) [12, 13]. An exchange of inorganic cations with organic cations renders the silicate organophilic and hydrophobic and lowers the surface energy of the platelets and increases the basal-plane or interlayer spacing (d-spacing) [12–16]. This improves the wetting, swelling, and exfoliation of the aluminosilicate in the polymer matrix. Alkyl ammonium ions like octadecyltrimethylammonium, dioctadecyldimethyl-ammonium, etc., have been conventionally used for the organic modification of silicates.
Nanocomposites with practically all the polymer matrices have been reported with varying degrees of property enhancements. Polar polymers have been gener-ally reported to achieve better filler dispersion owing to better match of the surface polarities of filler and polymers. On the other hand, the dispersion of filler in the nonpolar polymers like polyethylene, polypropylene, etc., is challenging owing to the absence of any positive interactions between the organic and inorganic phases. To circumvent these difficulties, either low molecular weight compatibilizers are added to the system or the filler surface is specifically modified by additional chemical or physical processes. The synthesis of nanocomposites has also been reported by a number of different ways, for example, melt compounding, in situ synthesis, solution mixing, gas phase processing, living polymerization, etc. All the different techniques to modify the filler surface as well as to synthesize the polymer nanocomposites need to be supplemented with robust characterization of these processes as well as resulting composite properties to gain insights into the various factors affecting the nanocomposite microstructure and properties so as to be able to design them according to the need.
1.2CharacterizationofMorphologyandProperties
Characterization of the nanocomposite materials is necessary to understand/analyze various facets of polymer nanocomposites. A few of them are listed as follows:
a) quality of dispersion of filler in the polymer matrix along with its orientation or alignment related to the processing method used,
b) effect of filler surface modification on filler dispersion and composite properties,
c) interactions of the filler modification with the polymer chains including chem-ical reactions between the two,
d) changes in the process parameters on the resulting morphology and proper-ties, and
e) apart from that, analysis of a wide spectrum of properties to ascertain the application potential of the nanocomposites.
1.2 CharacterizationofMorphologyandProperties 3
It is also, in many instances, necessary to employ more than one characteriza-tion technique in order to accurately characterize the nanocomposite material. For example, over the years, it has become common to divide the nanocomposites into intercalated and exfoliated types based on the reflections observed in the detection range of wide-angle X-ray diffraction (WAXRD). However, this classifica-tion is arbitrary because the observation of a peak in the diffractogram depends not only on the periodicity but also on other factors, such as the concentration and orientation of the aluminosilicates, and does not exclude the presence of exfoliated part. Its absence also does not exclude the presence of small or randomly oriented intercalated particles and, therefore, does not indicate complete exfolia-tion as often postulated. Figure 1.1 shows an example of polyurethane nanocom-posites generated with montmorillonite filler modified with different surface modifications [17]. The nanocomposites were synthesized by a solution casting method. The X-ray diffractograms of the filler Nanofil 804 (modified with bis(2-hydroxyethyl) hydrogenated tallow ammonium) as well as polyurethane nanocom-posites with different filler volume fractions are shown. The diffraction signals of the filler in the composites were shifted to lower angles confirming the intercalation of the polymer in the interlayers; however, the presence of diffrac-tion peaks also signified that the filler was not exfoliated. The extent of filler intercalation or exfoliation could not be quantified. When the same nanocompos-ites were characterized by transmission electron microscopy as shown in Figure 1.2, extensive filler exfoliation was noticed. The intercalated platelets also had varying thicknesses. Thus, to generate better insights into the nanocomposite microstructures, synergistic combinations of different characterization techniques are useful.
A number of different nanocomposite characterization methods are available which include thermogravimetric analysis, differential scanning calorimetry,
Figure1.1 X-ray diffractograms of the Nanofil 804 filler as well as polyurethane nanocompos-ites with different filler volume fractions. Reproduced from reference [17] with permission from American Chemical Society.
4 1 CharacterizationofNanocompositeMaterials:AnOverview
transmission electron microscopy, scanning electron microscopy, X-ray diffrac-tion, nuclear magnetic resonance, IR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, dielectric relaxation spectroscopy, atomic force microscopy, electron spin resonance, continuous-wave and pulsed ESR spectros-copy, etc. Apart from that, numerous characterization techniques to ascertain nanocomposite properties like mechanical performance, fire behavior, barrier performance, biodegradability, rheological properties, PVT characterization, tribo-
Figure1.2 TEM micrographs of the 2.86 vol% Nanofil 804-PU composite. Reproduced from reference [17] with permission from American Chemical Society.
1.3 ExamplesofCharacterizationTechniques 5
logical behavior, etc., are also used. The following section shows the overview examples of nanocomposite characterization performed with a few of these tech-niques; however, this section is not meant to be exhaustive.
1.3ExamplesofCharacterizationTechniques
Figure 1.3 [18] shows an example of thermogravimetric analysis (TGA) of the modified fillers. The characterization was carried out to ascertain the filler surface cleanliness so as to use them in high-temperature compounding or in in situ
Figure1.3 TGA thermograms of the (a) commercially modified BzC16; (b) self-treated BzC16; (c) commercially modified 2C18, and (d) self-treated 2C18. Reproduced from reference [18] with permission from Springer.
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6 1 CharacterizationofNanocompositeMaterials:AnOverview
polymerization processes. Fillers modified with sioctadecyldimethylammonium chloride (2C18) and benzylhexadecyldimethylammonium chloride (BzC16) were analyzed. As can be observed, the commercially treated fillers had an additional low-temperature degradation peak, which indicated the presence of excess surface modification molecules in the filler interlayers which were not ionically attached to the filler surface, but were physically trapped in the modification monolayers, thus forming pseudo bilayers. On the other hand, the self-treated fillers were free from any such excess molecules as no low-temperature degradation signal was observed in their thermograms.
Figure 1.4 shows an example of differential scanning calorimetry (DSC) char-acterization of pure polymer to generate information on the melting and crystal-lization transitions as well as to obtain information on the extent of crystallinity from the area under the melting transition (melt enthalpy). The nanocomposite materials can be similarly analyzed to know the effect of fillers on the crystalliza-tion behavior of the pure polymer. The organically modified fillers are also char-acterized by DSC in order to obtain information on the phase dynamics and transitions associated with the monolayers present on the filler surface.
Figure 1.5 [19] presents the WAXRD patterns of octadecytrimethylammonium (C18), dioctadecyldimethylammonium (2C18), and trioctadecylmethylammonium (3C18) modified fillers and their 3 vol% polypropylene nanocomposites. The analy-sis is used to ascertain the increase in interlayer spacing of the fillers after com-
Figure1.4 DSC thermograms of polypropylene using heating rate of 10 °C min−1 and cooling rate of (A) 10 °C min−1 and (B) 40 °C min−1.
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1.3 ExamplesofCharacterizationTechniques 7
pounding with polymers, which is related to the shifting of the diffraction peaks to lower diffraction angles. However, as mentioned earlier, the method does not provide quantification of the extent of intercalation and exfoliation. The filler in the composites in Figure 1.5 was observed to have similar basal plane spacing (as minimal shift in the diffraction peak angle) as the filler powders indicating no intercalation, but the tactoid thickness was observed to be decreased in the micro-scopy analysis and a partial exfoliation of the filler was achieved. The peak intensity in the diffractograms is also not an accurate indication of the extent of intercalation
Figure1.5 Wide angle X-ray diffractograms of (a) 1-3C18 ammonium modified fillers and (b) their PP nanocomposites. Reproduced from reference [19] with permission from Sage Publishers.
8 1 CharacterizationofNanocompositeMaterials:AnOverview
as it depends on other factors like filler concentration, filler orientation, defects in the crystal, and sample preparation methods, etc. Small-angle X-ray analysis is also carried out to analyze the materials in a very low diffraction angle range, which is not possible in the wide-angle X-ray techniques.
Microscopy is commonly used to complement the findings from X-ray diffrac-tion. Figures 1.6 and 1.7 show the scanning and transmission electron microscopy analysis of polymer nanocomposites [19, 20]. It should be noted that the filler
Figure1.6 SEM micrographs of 3 vol% 2C18 modified filler-PP nanocomposites. The filler platelets are visible in different orientation states. Reproduced from reference [19] with permission from Sage Publishers.
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1.3 ExamplesofCharacterizationTechniques 9
platelets are generally observed to be randomly aligned. Apart from misalignment, the platelets are also occasionally bent and folded. The particles of different thick-nesses also indicate that varying degrees of polymer intercalation in the filler interlayers takes place.
Similarly, out of a number of techniques available for characterization of func-tional properties of nanocomposites, two examples of gas barrier property and mechanical property characterization are shown in Figures 1.8 and 1.9, respectively
Figure1.7 TEM micrographs of the 3.5 vol% BzC16 filler – epoxy nanocomposite. The dark lines are cross-sections of aluminosilicate layers. Reproduced from reference [20] with permission from American Chemical Society.
10 1 CharacterizationofNanocompositeMaterials:AnOverview
[17, 21]. The oxygen permeation of the polyurethane nanocomposites as shown in Figure 1.8 is an interesting example as out of the three different fillers, two caused a decrease in oxygen permeation through the polymer, whereas the third filler led to an increase in the oxygen permeation as a function of filler volume fraction. The filler that led to an increase in the permeation was observed to have a least increase in the basal lane spacing as compared to the other two fillers. Also, the microscopy analysis had revealed minimum filler exfoliation in this case. Thus, such microstructure characterizations of the system could also be related to the resulting properties of the nanocomposites. In the example of the mechanical property characterization shown in Figure 1.9 for polypropylene nanocomposites generated with imidazolium modified filler, tensile modulus was observed to increase as a function of filler content, whereas the yield stress was observed to decrease. It indicated that though the load transfer from the polymer chains to the filler particles could take place resulting in an increase in modulus, the filler was still partially exfoliated and the thicker filler tactoids led to reduction in yield stress, which also corresponded with the microscopic characterization of the morphology which was partially exfoliated.
Figure1.8 Dependence of the oxygen transmission rate through the PU-nanocomposites on the inorganic volume fraction. Reproduced from reference [17] with permission from American Chemical Society.