Positronannihilationstudyonthinfilmcompo

Positronannihilationstudyonthin-filmcompositepervaporationmembranes:CorrelationbetweenpolyamidefinestructureanddifferentinterfacialpolymerizationconditionsShu-HsienHuangb,**,Wei-SongHunga,Der-JangLiawc,Hui-AnTsaid,GeorgeJ.Jiangb,Kueir-RarnLeea,*,Juin-YihLaiaaR&DCenterforMembraneTechnology,DepartmentofChemicalEngineering,ChungYuanUniversity,ChungLi32023,TaiwanbDepartmentofChemicalandMaterialsEngineering,NationalIlanUniversity,I-Lan26047,TaiwancDepartmentofChemicalEngineering,NationalTaiwanUniversityofScienceandTechnology,Taipei10607,TaiwandDepartmentofMaterialandFiber,NanyaInstituteofTechnology,ChungLi32034,TaiwanarticleinfoArticlehistory:Received27June2009Receivedinrevisedform17January2010Accepted30January2010Availableonline4February2010Keywords:InterfacialpolymerizationPolyamidePositronannihilationspectroscopy(PAS)abstractToinvestigatethevariationinthefinestructureofpolyamidethin-filmcomposite(TFC)membranespreparedviatwodifferentinterfacialpolymerizationconditions(IP-IandIP-II),experimentsonScanningElectronMicroscopy(SEM),AtomicForceMicroscopy(AFM),watercontactangle,andpositronannihila-tionspectroscopy(PAS)coupledtoaslowpositronbeamwereconducted.PolyamideTFCmembraneswerepreparedviatheinterfacialpolymerizationreactionbetweentriethylenetetramine(TETA)andtrimesoylchloride(TMC)onthesurfaceofamodifiedpolyacrylonitrile(mPAN)membrane.ComparedwiththepolyamideTFCmembranepreparedviaIP-I,thepolyamidelayerpreparedviaIP-IIshowedashorterSplateaulength(thinnerthickness),ahighero-PsintensityI3value(higherfree-volumeconcentration),andasmallero-Pslifetimes3value(smallerfree-volumesize),resultinginhigherpermeationrateandsepa-rationfactorobtainedfromthepervaporativeseparationofa70wt%isopropanolaqueoussolutionat25C.2010ElsevierLtd.Allrightsreserved.1.IntroductionInterfacialpolymerizationisbasedonareactionthatformsapolymerfilmattheinterfacebetweentwoimmisciblephases.Ineachofthesephases,ahighlyreactivemonomerisdissolved.PolyamideTFCmembranes,whicharepreparedbytheinterfacialpolymerizationofaminesandacylchloridesonporoussupportmembranes,arestudiedusuallyinreverseosmosis[1–5]ornano-filtration[6–10]processes.However,therehavebeenfewreportsonpervaporation[11,12].PolyamideTFCmembranesaremultilayered.Characterizationofmultilayeredmembranesincludesmostlychemicalandphysicalstructures.Characterizationofchemicalstructuresusinginstru-mentssuchasFourierTransformInfraredSpectroscopy(FTIR)[13,14]andElectronSpectroscopyforChemicalAnalysis(ESCA)[15],resultsinthedetectionofconfigurationandconformationalvaria-tions.CharacterizationofphysicalstructuresusinginstrumentssuchasAtomicForceMicroscopy(AFM)[16,17],ScanningElectronMicroscopy(SEM)[16]andTransmissionElectronMicroscopy(TEM)[18]resultsintheprobeofpropertiessuchasmorphologyandsurfaceroughness.Eachanalyticaltechniquehasitsadvantagesandshortcomingsinstructuraldeterminationandelementalsensitivity.Itisessentialtocharacterizemultilayeredmembranesbyusingseveraltechniques.Anovelphysicaltechnique,positronannihilationspectroscopy(PAS),canbeutilizedtomeasurephysicalpropertiesofmembraneswithmultiplelayers,suchasfreevolumes[19,20]attheatomicandmolecularlevelsasafunctionofchemicalchangesandmolecularmodificationsatdifferentdepthsinamultilayersystem.PASisapotentialphysicaltechnique.ThisisbecausemanystudiesonthephysicalpropertiesofpolymericmaterialsprobedbyPAShavebeeninvestigatedrecently[21–26].However,therearefewstudiesonpolymericTFCpervaporationmembranesinvestigatedwithPAS[20,27,28].Inthisstudy,thepolyamideTFCmembraneswerepreparedviatwodifferentinterfacialpolymerizationconditions(IP-IandIP-II)oftriethylenetetramine(TETA)andtrimesoylchloride(TMC)onamodifiedasymmetricpolyacrylonitrile(mPAN)membraneandwereappliedinpervaporationseparationprocess.Howtoprepareahighperformancepervaporationmembraneviathesimplestinterfacialpolymerizationprocessparameters,suchasthesup-portingmembraneandmembrane-makingconditions,reaction*Correspondingauthor.Tel.:þ88632654190;fax:þ88632654198.**Correspondingauthor.Tel.:þ88639357400;fax:þ88639357025.E-mailaddresses:[e-mail](S.-H.Huang),[e-mail](K.-R.Lee).ContentslistsavailableatScienceDirectPolymerjournalhomepage:–seefrontmatter2010ElsevierLtd.Allrightsreserved.doi:10.1016/j.polymer.2010.01.064Polymer51(2010)1370–1376time,monomerconcentration,andpost-treatmentconditions,isthemaingoalandoriginalideaofourpresentstudy.InthecaseofIP-I,adrymPANmembranewasusedtoprepareapolyamideTFCmembraneforpervaporation.ThisTFCpervaporationmembranepreparedviaIP-Iexhibitedgoodseparationperformance,butitrequiredhighermonomerconcentration,longerpolymerizationtime,andevenmoresevereannealingcondition,incomparisontothemembranefabricatedviaIP-II.However,inthecaseoftherevisedconditionsIP-II,asopposedtoIP-I,onlylowermonomerconcentrationandshorterpolymerizationtimeatroomtempera-turewererequiredtoprepareahighperformancepolyamideTFCpervaporationmembrane.BasedontheTFCmembranehavinggoodpervaporationperformance,itisinterestingtounderstandthecorrelationbetweenthepolyamide