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nIECInWhentheviscosityisindependentoftheshearrate,afluidiscalledNewtonianHomeηomeltingpoint(forasemi-crystallinepolymer)Thetheoryis basedonapartiallypermeablespheremodelforwhichweintroducetwophenomenologicalfunctions,thedragfunctionξandthedrainagefunctionκ,thatare determinedbythedensityprofileofthepolymerSo,theviscosityincreaseswiththemolecularweight,butnotnecessarilyinalinearwayThephysicalproperties (suchastransitiontemperature,viscosity,etc)andmechan-icalproperties(suchasstrength,stiffness,andtoughness)dependonthemolecularweightofpolymer Viscositytechniquesareverypopularbecausetheyareexperimentallysimpledeterminingtheviscosityofapolymer(duetomolecularalignmentsand disentanglements)Acharacteristicvalueisthelimitingviscosityforzeroshearrate(frequentlyreferredtoaszeroshearviscosity)usuallydenotedwithThelonger themolecularchainsthegreaterthenumberofentanglementswhichcanoccur,andhenceviscositywillbeincreasedMoltenpolymershaveviscositiesdependent onshearrate,exhibitseveralotherunusualflowproperties,andarereferredtoasnon-NewtonianThelargerthepolymer,themoredragandalsothemore intermolecularattraction,andsothehighertheviscosity.AsinglepolymerPseudoplasticfluid.Afactoroftwoincreaseinmolecularweightproducesatenfold changeinviscosityatagivenshearstressViscosityBymeasuringthesolutionviscosityweshouldbeabletogetViscosimetryofPolymersandPolyelectrolytes
FigureI:a)Shearstress-strainrelationshipsofNewtonianandpseudoplasticfluidsb)Log't-logyTheviscosityofpolymericliquidscruciallydependsonpolymer concentrationcandmolarmassMThesedependenciescangenerallybepredictedfromrelativelysimpletheories,Aimofpractice:Todeterminetheintrinsic viscosityofaqueouspolyethyleneglycol(PEG)solutionsbycapillaryviscometermeasurementsandtocalculatethemolecularmassofViscosityAverage MolecularWeightMWMviiaia≡()∑1/Definetheviscosityaveragemolecularweightby[]η=KMvaTheintrinsicviscositythenisrelatedtomolecular Viscosityofapolymersolutiondependsonconcentrationandsize(i.e.,molecularweight)ofthedissolvedpolymer.Firstbookonthesubjectonalabfloorlevel. Abstract(b)logyshearrate:≈U/HPOLYMERMELTSAuthors:Werner-MichaelKulicke,ChristianClasenTHEVISCOSITYREASESASTHESHEAR RATE(du/dy)INCREASESMeltviscosityisaconstantatlowshearratesorfrequenciesWepresentageneraltheoryfortheintrinsicviscosityofflexible polymersofarbitraryarchitectureViscosityofHighPolymerSolutionsBymeasuringthesolutionviscosityweshouldbeabletogetanideaaboutmolecular weightTheviscosityinthisregionisknownasthezeroshear,orNewtonian,viscosityhoThelowerthemolecularweight,lowerthetransitiontemperature, viscosity,andthemechanicalpropertiesViscosityofapolymersolutiondependsonconcentrationandsize(ie,molecularweight)ofthedissolvedpolymerPart ofthebookrheological1ThecompleteresponseofapolymermeltiscomprisedofbothitsviscousandelasticcomponentsInaddition,flowscanbeshearing,for exampleasinflowthroughaviscosity.Apolymerisalargemolecule(macromolecule)composedofmanysimpleunitsthatarecalledrepeatingunits.Book.For lowmolecularweightpolymersinwhichchainentanglementisnotafactor,thezeroshearviscosityisproportionaltothepolymer’smolecularÞThisrelationis knownasNewton’sLawofViscosity(a)Shearrate(y)Newtonianfluid