Lecture-Polymer-PhysicsPPT课件

.,1,LectureatECUST:PolymerPhysics,ShanfengWang,Ph.D.AssistantProfessor,TheUniversityofTennessee,Knoxville,DepartmentofMaterialsSciencetheissueofexperimentaltemperature;theircorrelation.,.,4,AFewImportantIssuesinPolymerScience,Glasstransitiontemperature(Tg);Viscoelasticity;Time-temperaturesuperposition;Modelsfordescribingpolymerdynamicswhenpolymerchainisatdifferentlengths.,.,5,LengthScaleandTimeScale,“ScalingconceptsinPolymerPhysics”byP.G.deGennes.,“Rheology:Principles,Measurements,andApplications”byChristopherW.Macosko.,“Variousanimalsattemptingtofollowascalinglaw”,“EventhemountainsflowedbeforetheLord”FromthesongofDeborahafterherVictoryoverthePhilistines,Judges5:5,.,6,MaterialsDesignStrategy:LengthScaleReallyMatters,Fabricationmethodsandproductdesign,Mechanicalproperties,biodegradability,etc,Kuhnlength,Packinglength,Entanglementlength,Radiusofgyration,Chainrigidity,Crystallization,Phaseseparation,Chainpacking,Self-assembledstructure,etc,A,o,nm,mm,mm,.,7,PolymerPhysics,CondensedStatePhysics,SoftMatter(orComplexFluid)Physics,StructureNatureofintermolecularbonding;Chainflexibility:segmentalmobilityishighlydependentonchainstiffness;Sidechainsubstitution:(1)ShortbulkygroupsincreaseTg(stiffenchainbyhinderingrotation);(2)LonglinearflexiblependantgroupslowerTg(internaldiluents,hinderpacking,increasefreevolume);(3)Non-symmetricalorsymmetricaldi-substitution.,.,14,Examples,Tg(oC),Dipole-dipole,Hydrogenbonding,ionic,Strongerionic,.,15,EffectofSideChainLengthonTgofPolymethacrylates,.,16,SummaryofFactorsThatAffectTg,IncreaseTg,IntermolecularforcesHighCohesiveEnergyDensityIntrachainsterichindranceBulky,stiffsidegroups,DecreaseTg,In-chaingroupspromotingflexibility(double-bondsandetherlinkages)FlexiblesidegroupsSymmetricalsubstitution,.,17,Plasticizers,Plasticizersarelowmolecularweightdiluents.TheyareusedtoincreasefreevolumeanddecreaseTg.Plasticizers:organic,highboilingpoint,weaklypolar.Tg:-150to50oC.Aromaticdiesters,phosphates.Example:PVC(polyvinylchloride)Tg=87oC.PlasticizerlowersTgandbroadenstransitionregionbetweenglassyandrubberyregion.,.,18,EffectofCopolymerizationorBlendingonTg,TheTgofablendorarandomcopolymercanbeestimatedfromthefollowingequationwhereDCpreferstothechangeinheatcapacityattheglasstransitionandMiisthemassfractionofcomponenti;ThisrelationisoftensimplifiedtotheFoxequation:BothoftheseequationsalsoapplytoplasticizerswhicharesmallmoleculesaddedtopolymerstoreduceTg.,.,19,GlassTransitionTemperatureofPolymerBlends,.,20,FiveRegionsofViscoelasticBehavior,Solidline:amorphouspolymer;Dashedline:semi-crystallinepolymer;Dottedline:crosslinkedamorphouspolymer.,.,21,RegionsofViscoelasticBehavior,Differenceisintherangeofmolecularmotionsthatarepossible.Glassregion:onlyvibrationalorshortrangerotationalmotions(1to4chainatomsinvolved).Glasstransitionregion:onsetoflongrangecoordinatedmotions(10-50chainatomsinvolved).Rubberyplateau:rapidcoordinatedmotionsofmuchofthechain:(1)forsemi-crystallineandcrosslinkedpolymersthechainsegmentsbetweencrystallitesorcrosslinksmoveinacoordinatedmanner;(2)forlinearamorphouspolymersthechainsegmentsbetweenentanglementscanmove.Flowregion:onlyexistsintheabsenceofcrosslinks,entirechaincanmoveinacoordinatedfashion(reptation).,.,22,EffectofMolecularWeightonLengthofPlateau,Thewidthoftheplateauisgovernedprimarilybythemolecularweight.Thehigherthemolecularweight,thelongeristheplateau.WhenthemolecularweightislowerthanNo.4,itispossiblefortheplateautodisappearduetothelackof“entanglement”.,.,23,Time-TemperatureSuperposition,Time-temperatureequivalenceimpliesthattheviscoelasticbehaviorcanberelatedtothatatanothertemperaturebyachangeinthetime-scaleonly!,.,24,AmorphousPolymers,Temperature,Deformation,Tg,Tf,Glassyregion,Glassytransitionregion,Rubberyplateauregion,Rubberyflowregion,Liquidflowregion,Glassyregion,Glassytransitionregion,Rubberyplateauregion,Rubberyflowregion,Liquidflowregion,.,25,DifferentPolymerSpecies(RubberorPlastics),-100,0,100,.,26,CrystallinePolymers,Crystallinity:1,234;Molecularweight:21,3,4,Crystallitescanbeconsideredasfillerstoincreasetheelasticmodulusandthereforetodecreasethedeformationwhenthesamestressisapplied.,.,27,EffectofCrosslinkingDensity,Crosslinkingdensity:123,PlasticizersaretodecreaseTg.,Plasticizersarelowmolecularweightdiluents.TheyareusedtoincreasefreevolumeanddecreaseTg.Plasticizers:organic,highboilingpoint,weaklypolar.Tg:-150to50oC.Aromaticdiesters,phosphates.Example:PVC(polyvinylchloride)Tg=87oC.PlasticizerlowersTgandbroadenstransitionregionbetweenglassyandrubberyregion.,.,29,MolecularWeight,Molecularweight:1234567,.,30,HowDoesViscosityhVarywithMolecularWeight?,Mc=2-3Me,Solid:experimentaldata;Dotted:Theoreticalpredictions.,.,31,PolymerDynamicsandRheology,(1)UnentangledSystemsa.Rousetheory-“free-draining”-beadandspring-pureunentangledmelt,DN-1tN2hN,(2)EntangledSystemsReptationtheory:Tube,DN-2thN3,Modification:Freevolumetheory(oriso-frictioncorrection),Modification:Contourlengthfluctuation,ConstraintRelease.,.,32,WhatisRheologyAnyway?,Rhe-:reiGreekfor“flow”;-ology:“studyof”.,“WhatisRheologyAnyway?”FaithA.Morrison.TheIndustrialPhysicist,10(2)29-31,April/May2004,Rheology=thestudyofdeformationandflow,“TheDeborahNumber”M.Reiner.PhysicsToday,62,January1964,.,33,PolymericMaterialsAreViscoelastic,ExhibitbothviscousandelasticbehaviorElastic-characteristicofsolids-reactlikeaspring,stressimmediatelydeformstostrain-recoversoriginaldimensionswhenstressremoved-strainisproportionaltotheappliedstress,butindependentoftherateofdeformationViscous-characteristicofliquids-instantresponsetostressisflow-tendtoirreversibledeformation-stressisproportionaltotherateofstrain.,.,34,Classicelasticandviscouslaws:HookeanLaw：NewtonianLaw：,Simplification:homogenous,isotropic,E:Elasticmodulus;G:Shearmodulus.,h:viscosity.,.,35,HookeansolidNewtonianLiquid,“Rheology:Principles,Measurements,andApplications”byChristopherW.Macosko.,AtshorttimesSillyPuttybehaveslikeaHookeansolid,butatlongtimesitbehavesmorelikeaNewtonianliquid.Thisbehaviorcanbenicelymodeledbyamodulusthatrelaxeswithtime,G(t).,.,36,“Rheology:Principles,Measurements,andApplications”byChristopherW.Macosko.,Mayonnaisespreadseasilyatthehighshearstressofthemovingknife,butleftaloneitwillsitinalumponapieceofbread.,HookeansolidNewtonianLiquid,ShearThinning,.,37,ShearThinning,Viscosity(h,Pa.s),Shearrate(g,1/s),tg1,.,.,tg1,.,.,.,38,RodClimbing(WeissenbergEffect),Normalforce,.,39,RodClimbingisnotasubtleeffect,asdemonstratedonthecoverbyPh.D.studentSylvanaGarcia-RodriguesfromColumbia.Ms.Garcia-RodriguesisstudyingrheologyintheMechanicalEngineeringDepartmentatU.ofWisconsin-Madison,USA.TheApparatusshownwascreatedbyUWMadisonProfessorsEmeritiJohnL.SchragandArthurS.Lodge.Thefluidshownisa2%aqueouspolyacrylamidesolution,andtherotationalspeedisnominally0.5Hz.PhotobyCarlosArangoSabogal(2006),RodClimbing,.,40,(N):FortheNewtonianfluidsthesurfaceneartherodisslightlydepressedandactsasasensitivemanometerforthesmallerpressureneartherodgeneratedbycentrifugalforce.,(N),(P),(P):ThePolymericfluidsexhibitanextratensionalongthestreamlines,thatis,inthe“”direction.Intermsofchemicalstructure,thisextratensionarisesfromthestretchingandalignmentofthepolymermoleculesalongthestreamlines.Thethermalmotionsmakethepolymermoleculesactassmall“rubberbands”wantingtosnapback.,PhenomenologicalInterpretation,.,41,ApplicationofWeissenbergEffect,Feedthepolymer,Rotateandmix,Extrudethepolymeroutfromtheexit,Weissenbergeffectoccurshere,.,42,DieSwell(BarusEffect),“UnderstandingRheology”byFaithA.Morrison.,dj/D1,Elasticrecovery,AstheliquidpolymerexitsAdie,thediameteroftheliquidIncreasesbyuptoanorderofmagnitude.Itiscausedbytherelaxationofextendedpolymercoilsasthestressinapolymericliquidreducesfromthehigh,flow-producingstressespresentwithinthedietothelowstressesassociatedwiththeextrudedstreammovingthroughambientair.,.,43,CapillaryFlowInstabilities,“UnderstandingRheology”byFaithA.Morrison.,Shapeslikeshark-skin,bamboo,etc.Shear:edgefracture(meniscusinstability)whenshearstressis104Pa.,.,44,SecondaryFlow,Secondaryfloweffectsmayoccurwhenmeasuringlow-viscosityfluidsathighshearratesandcanleadtoturbulences.However,theadvantageofsecondaryflowistomixthepolymersbetterinprocessing.,.,45,DuctlessSiphon:ExtensionalThickening,“Rheology:Principles,Measurements,andApplications”byChristopherW.Macosko.,Somenon-Newtonianfluidscanbestretchedoutofforshorttimeslikeasolid.WhenasiphonisslowlyremovedfromaNewtonianfluid,itbreaksveryclosetothesurface,butsomecomplexfluidscanbepulledupmanycentimetersabovethefreesurface.Polymericandothercomplexliquidscanshowmuchhigherviscositiesinextensionthaninshear.,Applications:Fiberspinningandfilmforming,.,46,Flow-inducedChange,Flow-inducedcrystallization.Associatingpolymersolutions.Micelles.Shearmixingandde-mixing.,Shear-inducedmixingisinterpretedasbeingadisruptionofslightlyentangledclustersundertheinfluenceoftheshearenergy.,.,47,NewtonianFluids,Newtonianfluidsshowtherelationshipbetweenshearstressandshearrateandthefluidsviscosityatavaryingshearrate.TypicalNewtonianfluidsincludewaterandthinmotoroils.,So,atagiventemperaturetheviscosityofaNewtonianfluidremainsconstantregardlessofwhichviscometermodel,spindleorspeedisusedtomeasureit.ThebehaviorofNewtonianliquidsinexperimentsconductedatconstanttemperatureandpressurehasthefollowingfeatures:theonlystressgeneratedinsimpleshearflowistheshearstress,thetwonormalstressdifferencesarezerotheshearviscositydoesntvarywithshearrate;theviscosityisconstantwithrespecttothetimeofshearingandthestressinliquidfallstozeroimmediatelytheshearingisstopped;theviscositiesmeasuredindifferenttypesofdeformationarealwaysinsimpleproportiontooneanother.Aliquidshowinganydeviationfromtheabovefeaturesisnon-Newtonian.,/phabdas/physics/rheo.html,.,48,Non-NewtonianFluids:Pseudoplastic,Theviscosityofnon-Newtonianfluidschangesastheshearrateisvaried.Thus,theparametersofviscometermodel,spindleandrotationalspeedallhaveaneffectonthemeasuredviscosity.Thismeasuredviscosityiscalledapparentviscosityandisaccuratewhenexplicitexperimentalparametersareadheredto.Thereareseveraltypesofnon-Newtonianflowbehavior,characterizedbythewayafluidsviscositychangesinresponsetovariationsinshearrate.,/phabdas/physics/rheo.html,Pseudoplastic:Fluiddisplaysadecreasingviscositywithanincreasingshearrate,someexamplesincludepaintsandemulsions.Thistypeofbehavioriscalledshear-thinning.,.,49,/phabdas/physics/rheo.html,Non-NewtonianFluids:Dilatant,Dilatant:Itischaracterizedbyanincreasingviscositywithanincreaseinshearra