PorometryStudiesofthePolysulfoneMembranesonAdditio

J.Mex.Chem.Soc.2008,52(2),140-144©2008,SociedadQuímicadeMéxicoISSN1870-249XArticlePorometryStudiesofthePolysulfoneMembranesonAdditionofPoly(ethyleneGlycol)inGelationBathDuringPreparationS.Javiya,Yogesh,S.Gupta,K.Singh,andA.Bhattacharya*ReverseOsmosisDiscipline,CentralSaltandMarineChemicalsResearchInstitute,CouncilofScientificandIndustrialResearch,Bhavnagar,Gujarat,India.E-mail:[e-mail]24deenerode2008;aceptadoel19demayode2008Abstract.Polysulfonemembranesarepreparedthroughphasesepara-tiontechnique,introducedbyLoeb-Sourirajan.Theviscouspolymersolution(indimethylformamide)isfirstspreadintothethinfilm,andthenimmersedingelationmedium(water).Theinfluenceofpoly-mericadditive,(poly(ethyleneglycol)(PEG))intheformationoftheporesduringphaseseparationingelationbath(i.e.fromthepolymerpoorphase,whichappearsatthephaseseparation)isexplored.Theeffectsofdifferentmolecularweight(Mw)ofPEGinthegelationbathregardingthedifferentialfilterflowsofnitrogenaswellastheirconcentrationarereflectedfromtheporometrystudies.Theporedis-tributionisshiftedasthemolecularweightofPEGusedinthegela-tionbath.ThebubblepointandmeanflowporediametersvarywiththeconcentrationaswellastheirmolecularweightofPEG.Keywords:Membrane,poly(ethyleneglycol),wetphaseinversion,gelationbath,porediameterResumen.Seprepararonmembranasdepolisulfonamediantelatécni-cadeseparacióndefase,introducidaporLoeb-Sourirajan.Lasolucióndelpolímeroviscoso(endimetilformamida)seesparcedentrodelapelículadelgada,ysesigueporunainmersiónenelmediodegelación(agua).Seexploralainfluenciadeladitivopolimérico(poli(etilénglicol)(PEG))enlaformacióndelosporosdurantelafasedeseparaciónenelbañodegelación(desdelafaseescasaenpolímero,lacualapareceenlaseparacióndefases).Delosestudiosdeporometría,seobservanlosefectosenlasdiferenciasenpesomoleculardelPEGenelbañodegelaciónsobrelosflujosdiferencialesdenitrógenoasícomodelaconcentración.LadistribucióndeporossedesplazadeacuerdoconelpesomoleculardelPEGempleadoenelbañodegelación.ElpuntodeburbujeoylamediaenlosdiámetrosdelosporosdeflujovaríanenfuncióndelaconcentraciónydelpesomoleculardelPEG.Palabrasclave:Membrana,poli(etilénglicol),inversióndelafasehúmeda,bañodegelación,diámetrodeporo.IntroductionTherecenteraofseparationscienceandtechnologyismostlybasedonmembranes,astheyareofeconomicandrequirelowenergy.Asaresult,therearevariousattemptstodevelopthemembranes.Theinventionof“asymmetricpolymermem-brane”byLoebandSourirajanistreatedoneofthebestfind-ingsinfieldofmembranescience.Theasymmetricmembranesareoftwoormorestructuralplanesofnon-identicalmorpholo-giesofpolymers.Theyareachievedthroughfourprincipalmethods:immersion-precipitation(wetphaseinversion),vapor–inducedphaseseparation,thermallyinducedphaseseparationanddrycasting[1].Thestructuresofthesetypeofmembranesaregreatlyinfluencedbythechangesinmembranepreparationconditionswhateverslightmaybe.Inthepresentinvestiga-tion,wet-phaseinversiontechniqueisfollowedtopreparetheasymmetricmembranes(Figure1).Inthistechnique,anini-tiallyhomogeneouspolymersolutionbecomesthermodynami-callyunstableandphaseseparatesinto“polymer-poor”and“polymer-rich”phases[2-6].Thepolymerpoorphaseformsthemembraneporesandpolymerrichsolidphaseformsthemembranehomogeneousstructure.Thediffusionexchangeofsolventandnon-solventinthepolymericsubstrateisthebasicmechanismofformationofthemembrane.Thepolymerrichphase(toplayer)isfirstformedatthepolymer-nonsolventinterface,andthenpolymerpoorphase(sublayer).Thus,inthepresentstudy,itisfocusedonphaseseparationpores,i.e.thecharacteristicsofthepolymerpoorphase.Thepreparationofasymmetricmembranesbyphaseinversionisadvantageoustogenerateporestructuresofthemembranes.Itisdonebyusingadditives(organicorinorgan-ic)aswell[7-11].Additivesarealsohelpfulininhibitionofmacrovoids,toimprovetheporeconnectivityandtoincreasehydrophilicity[8].Theconventionalapproachisaddingtheadditivesasthethirdcomponenttothecastingsolution.But,here,inthisstudypoly(ethyleneglycol)isaddedinwater-gelationbathasadditive.Thepolymericadditivesofdifferentmolecularweightarealsovariedtoinvestigatewhetheritcanchangetheporecharacteristicornot.ResultsandDiscussionInthe“phaseinversion”steppolysulfoneturnsintosolidstatefromthesolutionstateinpropersolvents(viz.DMF).Assoonasthepolymerincastingformcontactstothenon-solvent(water),itformsskinlayer.Phaseinversionaswellasskinlayerformationdependsuponthesurfacetensiongradients[12].Inotherwords,surfacetensiongradientsarethedrivingforcesaccountingfortheporestructureaswellastheforma-tionofasymmetriclayerinwhichside.AsinthiscasegPgS(P:PolymerandS:solvent),ittendstoformonthegela-tionbathside[13].Thus,thepresenceofwater(non-solventtothepolysulfone)ingelationbathresultsthedenseskinonthetopmostlayer.Dimethylformamideinthecastingsolu-tiondesolvatesrapidlyintothewatergelationbathasthereisstronginteractionofdimethylformamide(solvent)andwater(non-solvent).Whenthecastingsolutionandwatercomeintocontact,littlewater(non-solvent)diffusesintothecastingsolutionsinceitisanon-solventforPolysulfone.Ontheother00-RevSocQuímMex