Microstructures in phase inversion membranes.Part 2. The role of a polymeric additive

JournalofMembraneScrence,73(1992)277-292ElsevlerSciencePubhshersBV,Amsterdam277Microstructuresinphaseinversionmembranes.Part2.Theroleofapolymericadditive*R.M.Boom,I.M.Wlenk,Th.vandenBoomgaardandCA.SmoldersDepartmentofChemicalTechnology,UnwersltyofTwente,P0Box217,7500AEEnschede(TheNetherlands)(ReceivedJuly31,191,acceptedmrevisedformApril16,1992)AbstractMembraneswerepreparedfromacastmgsolutionofawater-solublepolymer,poly(vmylpyrrohdone)(PVP),andamembraneformingpolymer,poly(ethersulfone),ml-methyl-2-pyrrohdone(NMP)assolventbyimmersingthemmmixturesofwaterandNMPItwasfoundthattheaddltlonofPVPtotheternarysystemsuppressestheformatlonofmacrovoldsmthesub-layer,whiletheultraflltratlon-typetop-layerconsistsofacloselypackedlayerofnodulesUsingamodelformasstransfermthisquaternarysystem,it1spossibletoexplamtheeffectsoftheadditiveonmacrovoldformationStrongmdlcatlonsarefoundthattheappearanceofanodularstructuremthetop-layerfollowsamechanismofspmodaldecomposltlondunngtheveryearlystagesofthelmmerslonstepKeywordsmembranepreparationandstructure,theory,thermodynamics,macrovolds,phase-mverslonmembranesIntroductionPhasemverslonisthemostimportantpro-cesstopreparesymmetricorasymmetrlcmem-branesBecauseoftheslgmficanceoflmmer-slonpreclpltatlon(phasemverslon),themechanismofformatlonofthesemembraneshasbeenthesubjectofextensiveinvestlgatlon[1,2]Inrecent,years,Reuversetal[1]devel-opedamodelforthedescrlptlonofmasstrans-ferduringthelmmerslonstepTwotypesofde-CorrespondencetoRMBoom,DepartmentofChemicalTechnology,UniversityofTwente,P0Box217,750OAEEnschede,TheNetherlands*PaperpresentedattheIntSympon“ProgressmMem-braneScienceandTechnology”,Enschede,TheNether-lands,June2528,199l0376-7388/92/$050001992ElsevlerSciencePubhshersBVmixingoccurringduringimmersionpreclpltatlonfollowedfromthismodel.mstan-taneousdemlxmganddelayeddemixmg.Tak-mgthismodelofmasstransfermcombmatlonwithhquld-liquidphaseseparation,effectsofvariationsmthecomposltlonofthecastingso-lutionandthecoagulationbathcouldbeexplainedOnthebasisofthedist