Roughness o f g r owt h faces o f polymer

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1、Roughnessofgrowthfacesofpolymercrystals:EvidencefrommorphologyandimplicationsforgrowthmechanismsandtypesoffoldingDavidM.SadlerH.H.WillsPhysicsLaboratory,UniversityofBristol,RoyalFort,TyndallAvenue,BristolBS81TL,UK(Received6October1982;revised18January1983)Itisproposedthatthegrowthfacesoflamel

2、larpolymercrystalscanhaveanequilibriumroughness(orcrenellation).Thiscanexplainwhysomepolymercrystalsshownoevidenceoffaceting.Supportforthisideacomesfromtheextensivetheoreticaldevelopmentsonthenatureofcrystalsurfaces.Thecharacteristichabitsofpolyethyleneareanalysedintermsofaroughnesswhich,onth

3、e{110}faces,increasesprogressivelyoveratemperaturerangeofabout100.C.Atatemperaturenear110"Ctheroughnessbecomessufficientfortheretobenofreeenergypenaltyforarbitrarycrystalshapes(e.g.rounded)comparedwithoneboundedby{110}faces.Abovethistemperatureofcrystallizationmostof.thehabitswhichareobserved

4、areleaf-shaped,withanapexalong(010~.Below110.C{110}facets(ormicrofacets)arenormallyseen.Thereisnopositiveevidencethatfacesapproximatelyparallelto(100)planes,observedforcrystallizationtemperaturesintherange80"-110"C,areeverotherthanrough.Therelativeratesofgrowthonthe{110}comparedwiththe(100)in

5、creasewithtemperature,since{110}facespredominateatlowbutnothightemperaturesofcrystallization.Thesechangesareattributedtotheincreaseinroughnesswithtemperatureonthe{110}faces.Theexistenceofsurfacedisorder(roughness)requiresthatthebindingenergybetweenunitsinthecrystaliscomparablewithkT.Hencethis

6、unitisprobablyseveralmonomerunitsofpolyethylene(ratherthan,forexample,acompletestemwhichcontainsahundredormoremonomers).Thereisthereforeasurfacelatticeonthegrowthfaceswithtwentyormoreunitsinthedirectionperpendiculartothelamellae.MonteCarlocalculationsarecitedforlatticesof20by50units.Theseshow

7、thatacooperativeincreaseinsurfaceroughnesswithtemperatureandatransitionbetweenfacetedandnon-facetedgrowthcanbeexpectedforlatticesofsuchlimitedextents.Noexplicitallowancehasbeenmadeasyetfortheconsequencesoftheunitsbeinglinkedintochainsand,fort