Formation

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    ;ChineseChemicalLetters19(2008)988-991

    ;CHINESE

    ;CHEMICAt..

    ;LETTERS

    ;www.elsevier.com/locate/cclet

    ;Formationofsurface—attachedmicrostructured

    ;pO1ye1ectrO1ytebrushes

    ;HaiNingZhang

    ;StateKeyLaboratoryofAdvancedTechnologyforMateHalsSynthesisandProcessing ;WuhanUniversityofTechnology,Wuhan430070,China

    ;Received25January2008

    ;Abstract

    ;Surface?attachedmicropatternedpolyelectrolytebrushesonplanarsolidsurfacesaregeneratedusingfreeradicalpolymeriza?

    ;tionphoto—initiatedbyself-assembledinitiatormonolayers.Itisshownthattheformedpatternscanbeeithernegativeorpositive

    ;withdifferentpatterningprocesses.

    ;?

    2008HaiNingZhang.PublishedbyElsevierB.VonbehaffofChineseChemicalSociety.Allrightsreserved.

    ;Keywords:Microstructure;Self-assembly;Surface?initiatedpolymerization;Polyelectrolytebrush

    ;Polyelectrolyte1ayershavereceivedalotofaRentionsinboththeoreticalandexperiment~studies[1,2】.Theyare

    ;alsointerestingfromthepointofviewofapplicationsinmaterialscience[3】

    andbiology[4]aswel1.Ontheother

    ;hand,micropattemedpolyelectrolytelayersarealsousefulforthefabricationofsensors[5】

    andthespatial

    ;arrangementofbio—macromoleculessuchasproteinandDNA[6,7】.Furthermore,usin

    gpolyelectrolytestoform

    ;pattemedsurfaces,theformedstructureshavethepotentialtoformthemicrochannelstowhichanelectricfieldcanbe

    ;applied.

    ;Ifamaskisplacedovertheimmobilizedphoto—activeinitiatorlayerandthesubstrateisexp

    osedto254nin-UV

    ;lightinair,areasshadedbythemaskareinactivatedsincetheinitiatormoleculesaredecomposedbyirradiation.This

    ;leavesalatentimageforabarrieroffurtherpolymergrowth.Aftertheinitiatormonolayerisstructured,theradical

    ;polymerizationisinitiatedusingtheremainingintactinitiatormolecules.Thisapproachyieldsdirectgrowthof

    ;polymerchainsinthechosenareas,definedasprocessA,showninFig.1A.Theso—formed

    pattemedlayerisa

    ;“positivetone”image.Whenthemaskisplacedovertheimmobilizedinitiatorlayerandthesampleisirradiatedby

    365n//1.UV1ightinthepresenceofmonomer,reactiveradicalswillbegeneratedonlyatthe;

    fight-exposedareas,and

    ;accordingly.thepolymerizationwilltakeplaceonlywitl1intheseareas,definedasprocessB.Fig.1Bshowsthe

    ;processBfortheformationofpattemedpolymerfilms.Thisprocessleadstotheformationofpattemedfilmshavinga

    ;“negativetone”image.

    ;Microscopicimagesofthepattemedfilmsusingprocess”„areshowninFig.2.Theinitiatoru

    sedinthisstudyis

    ;anazo.typemolecule,chlorodimethylsilyl一3一

    ethylphenylazomethylmalonodonitrile(CSAM)asshowninFig.2b,

    ;whilchwasfirstimmobilizedonthesurfacesofsiliconoxidesubstrates.Synthesisandpropertiesofinitiatorandthe

    ;1001.8417/$一seefrontmatter?

    2008HalNingZhang.PublishedbyElsevierB.VonbehalfofChineseChemicalSociety.Allrightsreserved.

    ;doi:10.10160.cclet.2008.04.024

    ;一

    ;

    ;H.N.Zhang/ChineseChemicalLetters19l2008)988-991

    ;(A)(B)

    ;initiator

    ;monolayer

    ;UV

    ;mask

    ;—-

    ;上iii

    ;ilIitiator

    ;monolayar

    ;UV

    ;mask

    ;Fig.1.Schematicdepictionoftheformationofpatternedpolymerfilms.ProcessA:polymerlayergrownfromthepatternedinitiatorlayer;process

    ;B:polymerlayergrowndirectlyfromtheinitiatorlayer.

    ;detailedsurface—initiatedradicalpolymerizationprocesshavebeendescribedelsewhere【8—10].Thesamplewas

    ;patternedbVUVirradiationwithwavelengthof254Rrnfor5husingstructuredcopperasmask,rinsedextensivelyand

    ;driedinvacuum.ThenitwastransferredtoaSchlenk-tubeandsurface—initiatedpolymeri

    zationofmethacrylicacid

    ;(MAA)wascarriedoutinaqueoussolution(MAA:H201:1,v/v‟3h)using365amUVlight.Afterpolymerizationthe

    attachedpolymersandwasd;samplewasextractedwithethanolinordertoremovethenon—

    riedunderani~ogenflow

    ;andlaterundervacuum.Thethicknessofthepoly(acrylicacid)(PMAA)flllnsWaSmeasuredonareasofsubstrate

    ;whichcarrynopaRernsas210Rrnbyellipsometry.Becauseinthoseareasthesameinitiatorwasusedandthesame

    ;polymerizationconditionswereappfied,itcanbeassumedthatthethicknessofthepaRernedfilmisthesameasthatof

    ;withoutpatterns.ThewidthofasquareshowninFig.2is200mandtheline—widthis35m.

    ;Fig.3showstheatomicforcemicroscopy(AFM)imageofthefinesinthepattern.Fromthesectionanalysisofthe

    ;删

    image,theaveragethicknessofthepatternedfilmwascalculatedas223Rrn,whichagreesverywellwitll

    ;thicknessmeasuredbyellipsometry.Theformedpatternhasrathersharpboundariesbetweenareascoatedwitll

    ;polymerandthosewithoutpolymer.Interestingly,thethicknessofthePMAAlayersattheedgeoftheformedfilmis

    ;C

    ;cI——

    ;占

    ;CN

    ;H3

    ;Fig.2.(a)ThemicroimagesofpatternedPMAAfilmsformedbytheprocessA,schematicallyshowninFig.1usingthepatternedCSAMinitiator

    ;layers.ThepolymerizationtimeWaS3hunderUVirradiation(365nm).Thethicknessofformedfilmsisaround210nlnbaseduponempsometry

    ;measurements.(b)ChemicalstructureoftheinitiatorCSAM.

    ;.

    ;呲删肿

    ;，=耋，，‟g.一

    ;.，，，，

    ;

    ;H.N.Zhang/ChineseChemicalLetters19(2008)988-991

    ;Fig.3.AFMimagesofoneofthefinesintheformedpatterninFig.2.Theaveragethicknessofthepolymerlayeris223hil1.

    ;slightlyhigherthanthatinthemiddleofformedfilms.Thismightresultfromthehumidair,inwhichtheWater

;moleculescanwettheP】

    AA1ayerandminimizethesurfaceenergyofthePMAAlayer.TIliSphenomenonis ;somehowlikewaterbehavinginahydrophiliccapillary.

    ;Inthesecondapproach(processB),amaskisplacedovertheimmobilizedinitiatormonolayerandthesubstrateis

    ;placedinmonomersolutionandirradiatedwith365nmUVlight.Hence.thepolymerizationtakesplaceonlyinthe

    ;areasexposedtotheUVlight.asshowninFig.1B.TheSO.formedfilmshaveanegativeimage.Arnicroimageofa

    ;patternedPMAAfilmformedbythisprocessisshowninFig.4.Themaskusedherewasapoly(tetrafluoroethylene)

    ;(PTFE)pelletwithahole(radius:3mm).ThepolymerizationwascarriedoutwithMAAinaqueoussolution

    ;(MAn:H7O1:1,v/v)for6h(continuousexposuretoUVlightwithwavelengthof365nm).Afterextractionofthe

    ;non.adsorbedpolymermoleculeswithethanolfromthesubstrate,thesamplewasdriedunderanitrogenflowandlater

    ;undervacuum.Thethicknessoftheformedfilmintheareas,whichwereexposedtotheUVlight(throughthehole)

    ;Fig.4.ThemicroimageofapatternedPMAAfilmformedbytheprocessBasshowninFig.1usingtheself-assembledCSAMinitiatormonolayer.

    ;

    ;H.N.Zhang/ChineseChemicalLetters19f2oo8)988-991991

    ;wasmeasuredwithellipsometryas360nin.However,alSOsomepolyrmerswereattachedtothoseareas,whichwerg

    ;notdirectlyexposedtotheUVlight.TSisduetothefactthatthemaskwasplacedratherfarfromthesubstratef3—

    ;4mm)andthescatteredUVlight.afterpassingthroughthemaskmaydecomposetheinitiatoronthelatterareaas

    ;wel1.I1liSproblemCanbesolvedifthemaskisplacedcloseenoughtothesubstrate. ;Insummary,surface-attachedmicropatternedpolymerbmshesCanbeeasilyfabricatedusingfreeradioal

    ;polymerizationinitiatedbyanimmobilizedinitiatorlayer.Witlldifferentprocesses.eitherpositiveornegativeimages

    ;Canbeformed.?

    leusingprocessBdescribedabove.surfacesarepatternedbyareasofpolymerbrushesandareasof

    ;unreactedinitiatormonolayer,whichmakestheformationofpatternedpolymerbrusheswithdifferentcomponentsat

    ;thesurfacepossible.

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