Electric Field Mediated Transport in Nanometer Diameter.pdf

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1、2884Langmuir1998,14,2884-2889ElectricFieldMediatedTransportinNanometerDiameterChannelsPaulaJ.Kemery,²JackK.Steehler,³andPaulW.Bohn*,²DepartmentofChemistryandBeckmanInstituteforAdvancedScienceandTechnology,UniversityofIllinois,600SouthMathews,Urbana,Illinois61801,andDepartmentofChemistry,RoanokeColl

2、ege,Salem,Virginia24153ReceivedFebruary5,1998Nanoporouspolycarbonate(PCTE)nuclear-track-etchedmembraneswereusedtoeffectelectricfieldmodulationofthemasstransportofcationic,anionic,andneutralspeciesinaqueousbuffer.Thepermeabilityresponsetoelectricfieldsdependedonthemolecularchargeandelectrolyteconcen

3、tration.Soluteandsolventfluxesthroughnanoporesunderanelectricalpotentialresultfromabalanceofdiffusion,electroosmosis,andionmigration.TheDebyelength,-1,associatedwiththeelectricaldoublelayerwithintheporesrelativetotheporediameter,2a,playsacriticalroleindeterminingelectrokinetictransportbehavior.The

4、channelwallsadsorbanionspreferentiallytoproducealargelyimmobilenegativechargedensity,leavingalargeandmobilecationpopulationtomediatetransportinthechannel.Byadjustingthesupportingelectrolyteconcentration,acanbetunedsuchthattheelectricaldoublelayeriseithersmallinrelationtothepore(ag1)ormorediffusea

5、ndspanningthepore(a<1).Electroosmotictransport,mediatedprimarilybybuffercations,dominateswhena<1.Inthiscasetheporesareessentiallypermselective,andanionelectromigrationisvirtuallyeliminated.Whenag1,thesignoftheappliedpotentialcanbeusedtoselectforanionvscation/neutralmoleculetransport.Introduction

6、fluxoscillations.12Surfacecharge,amanifestationoftheenhancedsurfacearea-to-volumeratio(As/V),isacriticallyIncreasingly,thebehaviorofverysmallensemblesofimportantpropertyinfluencingallthesephenomena.13,14moleculesiscomingunderscrutiny,makingitimperativeItdeterminesthemagnitudeofthesurfacepotentialan

7、dthattoolsbedevelopedformanipulatingmicroscopictheapplicabilityoftheDebye-Huckelapproximation,andquantitiesofmaterialswiththesamefacilitynowavailableultimately,itprovidesanexperimentalhandletoadjustformacro