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lableatScienceDirectPolymer51(2010)2825e2835ContentslistsavaiPolymerjournalhomepage:www.elsevier.com/locate/polymerCarboxylicacid-functionalized,coreeshellpolystyrene@polypyrrolemicrospheresasplatformsfortheattachmentofCdSnanoparticlesAhmedMadania,BelkacemNessarka,*,RobertaBraynerb,HamidElaissaric,MohamedJouinib,ClaireMangeneyb,*,MohamedM.Chehimib,*aLaboratoired’ElectrochimieetMatériaux,DépartementdeGéniedesProcédés,FacultédesSciencesdel’Ingénieur,UniversitéFerhatAbbas,Sétif19000,AlgeriabInterfaces,Traitements,OrganisationetDynamiquedesSystèmes(ITODYS),UniversitéParisDiderot&CNRS(UMR7086),15rueJeandeBaïf,75013Paris,FrancecClaudeBernardUniversityLyon-1.LAGEPLaboratory,CPE-308G43Bd.11Novembre.1918/69622VilleurbanneCedex,FrancearticleinfoArticlehistory:Received15January2010Receivedinrevisedform29March2010Accepted9April2010Availableonline21April2010Keywords:PolypyrroleCoreeshellparticlesCdSnanoparticles*Correspondingauthors.Tel.:þ33144276809;faxE-mailaddresses:b.nessark@yahoo.fr(B.Nessdiderot.fr(M.M.Mangeney),chehimi@univ-paris-dide0032-3861/$eseefrontmatter
2010ElsevierLtd.doi:10.1016/j.polymer.2010.04.020abstractPolypyrrole-coatedpolystyrenelatexparticlesbearingN-carboxylfunctionalgroups(PS@PPyCOOH)werepreparedbythein-situcopolymerizationofpyrrole(Py)andtheactivecarboxyl-functionalizedpyrrole(PyCOOH)inthepresenceof390nmdiameter-sizedpolystyrene(PS)latexparticles.UncoatedPSparticleswerepreparedbyemulsionpolymerizationofstyrene.Theinitialcomonomerfractions(inmol%)were25/75,50/50,75/25and100/0forpyrroleandPyCOOH,respectively.ThePS@PPyCOOHxparticles,wherexstandsfortheinitialmolarfractionofPyCOOH(x¼0,25,50or75%),werechar-acterizedintermsofparticlesize,surfacemorphology,chemicalcompositionandelectrochemicalredoxactivityusingtransmissionelectronmicroscopy(TEM),X-rayphotoelectronspectroscopy(XPS),FTIR,TGAandcyclicvoltammetryrespectively.TEMshowedanincreaseofthelatexparticlediameteraftercoatingbytheconductingpolymerlayer,from390nmforuncoatedPSto430nmforPS@PPy-COOH50particles,allowinganestimationofthePPyCOOHshellthicknessto20nm.FTIRandXPSdetectedPyCOOHrepeatunitsatthesurfaceofthelatexparticles,indicatingthatthismonomerhadindeedcopolymerizedwithpyrrole.ThecoreeshellstructureofthePS@PPyCOOHxparticleswasconfirmedbyetchingthepolystyrenecoreinTHF,leadingtotheformationofhollowconductingpolymercapsules.PositivelychargedCdSnanoparticleswereelectrostaticallyassembledontothesurfaceofPS@PPyCOOH50particles,asafunctionofpH.Itwasfoundthat,contrarilytounfunctionalizedPPy-coatedlatexparticles,PS@PPyCOOH50particlescouldbeevenlydecoratedwithstabilizedCdSnanoparticles,atpH5.ThefilmsofthePS@PPyCOOH@CdS-coatedITOelectrodesareshowntobeelectroactiveandelec-trochemicallystable.
2010ElsevierLtd.Allrightsreserved.1.IntroductionCore@shellparticleswithconductivepolypyrroleshellscoatedoninorganic[1e4]orpolymericcores[5e9]havebeenthesubjectofnumerousstudiessincethelate1980s.Indeed,polypyrrole-coatedparticleshaveenormousscientificandtechnologicalinterestspertainingtothedevelopmentofvisualbiomedicaldiagnostics[1c,9e],conductivecomposites[3e,7a],conductivepaints[5b],anticorrosioncoatings[8b],stationaryphaseinliquidchromatography[4g],conductivepigments[3f],hypervelocityexperimentswithmicroprojectilesofpolypyrrolemimickingsolardusts[6].:þ33144276814.ark),mangeney@univ-paris-rot.fr(M.M.Chehimi).Allrightsreserved.Amongthemainconductivepolymers,polypyrrole,polyaniline,polythiopheneandpoly(ethylenedioxythiophene),theformerhasperhapsthebroadestpotentialapplicationsduetotherelativeeaseofitssynthesisviasimplebeakerchemistry.Inaddition,poly-pyrrole(genericname)canbepreparedintheformofreactiveandfunctionalcopolymers[1c,2a,10]whichisanimportantissueregardingtheimmobilizationofmetallicnanoparticlesandothernano-objects.Inthisregard,Chenetal.[11]havedemonstratedaonestepfacileandversatilesyntheticroutetoPPyeAgnano-compositesbychemicaloxidativepolymerizationofpyrroleusingsilvernitrateasanoxidationagentinaqueousmedia.Henryetal.[12]suggestedthatPdCl2actsasanefficientoxidantforpyrroletoformPPyePdcompositesinaqueousmedia.Asfaraswearecon-cerned,wehaveproposedtoimmobilizepreformedgoldnano-particlesontoamino-functionalizedpolypyrrole-coatedPS(PS@PPyNH2)microspheres[9f],andhumanserumalbuminA.Madanietal./Polymer51(2010)2825e28352826(aglobularprotein)ontoN-activeesterfunctionalizedpolypyrrole-coatedpolystyrenemicrospheres[9a,b,c,d,e].Theseexamplesshowtheimportanceofcontrollingtheinter-facechemistrythatoperatesatthesurfaceofpolypyrroleinordertoobtainnovel,robustfunctionalheterostructureswithsupportedglobularnano-objects.Inacontinuousefforttoexplorethesurfacereactivityandapplicationsofpolypyrroleparticles,weaimedatinterrogatingthepropensityoftheseconductiveshellsfromPS@PPymicrospherestobindCdSquantumdots(QDs).Inthisregard,itisessentialtoconsidertheelectrostaticinteractionsthatoccurbetweentheQDsandtheunderlyingPS@PPymicrospheres.TheefficientstrategydevisedsofarforbindinggoldnanoparticlestoPS@PPyNH2[9f]canthusbeadoptedandtunedtowardstheeffectiveimmobilizationofCdSQDs.TherationaleforimmobilizingCdSnanoparticlesisthatonecanobtainsupportedfluorescentsQDsanddesignbythiswaynovelheterostructureswithsynergeticeffectsofconductivity(owingtopolypyrrole)andopticalpropertiesimpartedbyCdS.Alternatively,CdSQDscouldactassupportedphotocatalysts[13],photoinitiatepolymerizationreactions[14],orenhancethesensi-tivityofpolypyrrole-basedbiosensors[15].Still,itisimportanttocontrolthemechanismsofCdSimmobilization.Inthepresentwork,wedescribethepreparation,character-izationandelectrochemicalpropertiesofacid-functionalizedpolypyrrole-coatedpolystyrenemicrospheresdecoratedbyCdSnanoparticles(PS@PPyCOOH@CdS)(seeFig.1).Thepolystyrenecore,averagediameter390nm,waspreparedbyemulsionpoly-merizationofstyreneandpoly(N-vinylpyrrolidone)wasusedasastericstabilizer.ThereactiveconductingpolymercoatingsconsistofcopolymersofpyrroleandN-alkylsubstitutedpyrrolewithN-carboxylicacidgroups(PyCOOH)atthealkylchainend.Variouspoly(Py-co-PyCOOH)-coatedPSlatexparticleswerepreparedwithfourdifferentcomonomerfeedratios(PS@PPyCOOHx;xbeingtheinitialfractionofPyCOOH).Thecoreeshellparticleswerecharac-terizedbymeansoftransmissionelectronmicroscopy(TEM),FTIR,X-rayphotoelectronspectroscopy(XPS)andTGA.Polypyrrolehollowparticleswerethenpreparedbyselectiveextractionofthepolystyrenecore.SelectedbatchesofparticleswereincubatedwithCdSnanoparticlesinordertomonitortheformationofassembliesbetweenthecarrier(PS@PPyCOOH)andthesupportednano-particles.CyclicvoltammetrywasusedtoevaluatetheredoxpropertiesoftheQD-decoratedcore/shellmicrospheres.2.Experimental2.1.MaterialsStyrene(Aldrich)waspurifiedbypassingthroughacolumnofactivatedneutralalumina.Poly(N-vinylpyrrolidone),withanominalmolecularweightof360000,waspurchasedfromAldrichandusedwithoutfurtherpurification.Pyrrole(Fluka)waspurifiedbypassingthroughacolumnofactivatedbasicalumina(Arcos)priortouse.SPSPlCeF3HOOCyP/yPresilibatsPVNP--------Fig.1.SchematicrepresentationofthesynthesisofPPyCOOH-coated,PNVP-stabilizedPSlnegativelycharged,coreeshellpolypyrrole-polystyrenelatexparticlesbearingsurfacedepr1-(2-cyanoethyl)pyrrole(Acros),FeCl3$6H2O(Aldrich),ethyleneglycol(Acros),lithiumperchlorate(LiClO4)(Acros),thiourea(Aldrich),cadmiumacetate(Fluka)anda-azoisobutyronitrile(AIBN)(Fluka)wereusedwithoutfurtherpurification.TheN-2-carboxyethylpyrrolecomonomerwassynthesizedasdescribedinRef.[2a].Allaqueoussolutionswerepreparedwithdeionisedwater.2.2.Synthesisofsurfacefunctionalizedpolypyrrole-coatedpolystyrenelatexparticlesPolystyrenemicrosphereswerepreparedbyemulsionpolymer-izationasreportedintheliterature[5c].Priortotheoxidativecopolymerizationofpyrroles,thePSparticleswereprecoatedwithPNVPasdescribedin[9g].Theconductivepolymercoatingproce-dureconsistsinthein-situcopolymerizationofpyrrolesinthepresenceofpolystyrenelatex.PyrroleandPyCOOHwerepremixedin25/75(0.059mmol/0.177mmol),50:50(0.118mmol/0.118mmol),75:25(0.177mmol/0.059mmol)and100:0(0mmol/0.236mmol)molarratios.Thiscomonomermixturewasaddedtoavigorouslystirredsolution(5ml)containing0.1gdryweightofPSlatexand0.09gofFeCl3$6H2O.Thesolutionwasstirredatroomtemperaturefor16h.Theresultingcolloidalparticleswereisolatedbyfivecentrifugation/redispersioncyclesandredispersedindeionisedwater.Thecompositepoly(Py/PyCOOH)-coatedPSparticlesareabbreviatedasPS@PPyCOOHxwherexstandsfortheinitialmolarfractionofPyCOOH(x¼0,25,50or75%).ThepolystyrenecorewasselectivelyextractedfromPS@PPyCOOHxlatexparticlesusingTHF.Thesolutionwasstirredatroomtemperaturefor24handtheresultinghollowcapsuleswereisolatedbyfivecentrifugation/redispersioncycles.2.3.SynthesisofCdSCdSnanoparticlesweresynthesizedinethyleneglycol(EG)usingthePolyolmethod[16e18].Basically,cadmiumacetateandthioureawereaddedtoan80mlofpolyoltoreachafinalconcentrationbetween0.006and0.6moll1.Themixturewasthenheatedat120Cundervigorousstirringduring1h.2.4.CoatingofPS@PPyCOOHxwithCdSnanoparticles800mlofCdSnanoparticlesinaqueoussolution(60mgml1)wereaddedto200mlofPS@PPyandPS@PPyCOOH50latexparti-clessuspension(32mgml1)andthemixturewaslefttoreactfor16h.ThepHofthemixturewasadjustedtovariousvalues(2,4,5,8,and10)byadditionofHCl(foracidicsolutions)andNaOH(forbasicsolutions).Afterincubation,thesampleswerecentrifugedandwashedthoroughlywithdistilledwaterinordertoremovethefreeand/orlooselyboundnanoparticles.TheproductswerecharacterizedbyTEMandXPS.ItistonotethatthepHsetasOOCyP/yP(yloP-)++++++++SP++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------sPNSdCatexparticlesandassemblyofpositivelychargedCdSnanoparticlesonthesurfaceofotonatedN-ethylcarboxylgroups.Fig.2.TEMmicrographsof(a)PS@PPy;(b)PS@PPyCOOH25;(c)PS@PPyCOOH50and(d)PS@PPyCOOH75latexparticles.Table1PropertiesofPNVP-stabilizedPS,PS@PPyandPS@PPyCOOHxlatexparticles.SamplesDiameter(nm)PolydispersityindexShellthickness(nm)PPymassloadingwt.%PS3901.008eePS@PPy4601.0093549.0PS@PPyCOOH254401.0102539.5PS@PPyCOOH504301.0092033.8PS@PPyCOOH754101.0101019.5A.Madanietal./Polymer51(2010)2825e28352827mentionedabovewasstableduringthetimescaleofCdSadsorptionexperiments.2.5.AnalyticaltechniquesTransmissionElectronMicroscopy(TEM)micrographswereobtainedusingaJEOLJEM100CXIIUHRoperatingat100kV.SolutionscontainingthelatexparticleswerecastontoFormvar-coatedcoppergridsandthesolventwasallowedtoevaporate.FTIRspectrawererecordedusingaNicoletMagna550SeriesIIinstrument.Spectraweretypicallyaveragedover20scansat4cm1resolution.X-rayphotoelectronspectroscopy(XPS)measurementswereperformedusingaThermoVGESCALAB250instrumentequippedwithamonochromaticAlKaX-raysource(1486.6eV).TheX-rayspotsizewas650mm.Thepassenergywassetat150and40eVforthesurveyandthenarrowscans,respectively.Chargecompensa-tionwasachievedwithacombinationofelectronandargonionfloodguns.Theenergyandemissioncurrentoftheelectronswere4eVand0.35mArespectively.Fortheargongun,theenergyandtheemissioncurrentwere0eVand0.1mA,respectively.Thepartialpressurefortheargonfloodgunwas2108mBar.Thesestandardconditionsofchargecompensationresultedinanegativebutperfectlyuniformstaticcharge.DataacquisitionandprocessingwereachievedwiththeAvantagesoftware,version1.85.SpectralcalibrationwasdeterminedbysettingthemainC1scomponentat285eV.Thesurfacecompositionwasdeterminedusingthemanufacturer’ssensitivityfactors.ThefractionalconcentrationofaparticularelementA(%A)wascomputedusing:%A¼ðIA=sAÞPðIn=snÞ100WhereInandsnaretheintegratedpeakareasandtheScofieldsensitivityfactorscorrectedfortheanalyzertransmissionfunction,respectively.Thermogravimetricanalysis(TGA)wasperformedonaSETARAMTGA92-12.TGAexperimentswereconductedinflowingairataramprateof10C/min.2.6.ElectrochemistryAtraditionalthreeelectrodesone-compartmentelectro-chemicalcellsystemwasusedinelectrochemicalexperiments.Glassycarbondisc(4mmdiameter)orIndiumtinoxide(ITO)wereusedasworkingelectrodes.Platinumgridandsaturatedcalomelelectrode(SCE)wereusedascounterelectrodeandreferenceelectroderespectively.Thecyclicvoltammetry(CV)andelectro-chemicalimpedancespectroscopy(EIS)techniqueswereper-formedusingEC-LabExpressV5.12ModelVSPBiologic.LiClO4(0.1M)wasusedassupportingelectrolyte.3.Resultsanddiscussion3.1.Characterizationofpolypyrrole-coatedPSlatexparticles3.1.1.TEMFig.2displaysTEMmicrographsofPS@PPy,PS@PPyCOOH25,PS@PPyCOOH50andPS@PPyCOOH75particles.Itisworthnotingthatparticlesaresphericalwithadiameteraround430nm.ThecomparisonbetweenPSandPS@PPyCOOHxparticlesevidencessignificantmodificationsofthesurfacemorphologyfollowingcoatingwiththeconductingpolymershell.TheuncoatedPSparticles(TEMmicrographnotshown)haveasmooth,featurelesssurfacemorphology.Incontrast,forPS@PPyCOOHxparticles,theconductingpolymeroverlayerinducesrougheningofthesurfaceaswehaveobservedforamineandN-succinimidylesterfunctionalizedPS@PPymicrospheres[9d,e,f].ThesurfaceroughensforhigherinitialpyrrolefeedratiobutgetssmootherwhenthePyCOOHfractionincreases.Forexample,whilstPS@PPyandPS@PPyCOOH25particlesexhibitsmallraisedgranularpolymernodules,PS@PPyCOOH50andPS@PPyCOOH75particlesexhibitmuchsmoothersurfaces.Thenumberaveragediameter(Dn)andthepolydispersityparameter(Dv/Dn)ofparticlesweremeasureddirectlyfromtheTEMimages.Typically,thesizesof50particlesweremeasuredandthevalueswereaveraged.TheDnandDvwerecalculatedfrom:Dn¼PiNiDiPiNiandDv¼PiNiD4iPiNiD3iwhereDimeansthediametersofindividualparticlesandNireferstothenumberofparticlescorrespondingtothediameters.AsshowninTable1,thenumberaverageparticlediameterincreasesfromca.390nm(Dv/Dn¼1.008)forPSparticlestoca.430nm(Dv/Dn¼1.009)forPS@PPyCOOH50particles.ThedifferencebetweenthediametersoftheuncoatedPSparticlesandtheconductingpolymer-coatedPSparticlesgivesanestimationoftheconductiveoverlayerthickness.ThePPyCOOHxthicknessdecreaseswithincreasinginitialPyCOOHcomonomerfeedratio.Thistrendismostprobablyduetothesterichindrancebroughtbythecarboxylacid-terminatedpendentalkylchainendofthePyCOOHcomonomer,Fig.4.TEMmicrographsofVoid@PPyandVoid@PPyCOOH50hollowcapsulesobtainedbypolystyrenecoreetchinginTHF.A.Madanietal./Polymer51(2010)2825e28352828whichhampersthepolymerizationprocess.Asamatteroffact,attemptstopreparethehomoPPyCOOHshellwereunsuccessful.Fromthethicknessofthepolypyrroleoverlayeranditscorre-spondingvolume,andassuminganaveragedensityof1.5fortheconjugatedpolymer[2c,19]itispossibletoestimatethemassloadingofpolypyrrole.ForPScore,thedensityisassumedtobe1andforthevariouspolypyrrole-coatedPSparticlesthemassloadingofpolypyrrolewascomputedusing:Wt%¼massPPyperparticleðmassPPyþmassPSÞperparticle100ThemassloadingvaluesarereportedinTable1.InthespecificcaseofPS@PPyCOOH50microspheres,TGAwasusedtoassesstheexperimentalmassloadingoftheconjugatedpolymeroverlayer.Fig.3showsthemasslossexpressedasapercentagemassofPS@PPyCOOH50versustemperature.Thethermogramdisplaystworegions:thefirstonecorrespondstothecalcinationofpolystyrene(wt.loss¼72.45%atT¼354C);andthesecondregioncorrespondstothecalcinationofPPyCOOH(27.55wt.%atT¼520C).TheexperimentalpolypyrrolemassloadingisinfairagreementwiththatcalculatedfromTEMandreportedinTable1.InordertocheckwhetherPS@PPyCOOHxparticlesareindeedofthecoreeshelltype,hollowPPyCOOHxmicrocapsuleswerepreparedbyextractingthepolystyrenecoreinTHF.TEMmicro-graphsofhollowPPyCOOHx(Void@PPyandVoid@PPyCOOH50)areshowninFig.4,indicatingsignificantdifferencesinthestructuresoftheshellsafterselectiveextractionofPScore.Indeed,unbrokenVoid@PPyCOOH50particleswereformedfromPS@PPyCOOH50(thisissimilartothecaseofPS@PPyCOOH75)whilePS@PPy(andPS@PPyCOOH25,notshown)ledtobrokenVoid@PPyhollowparticles.Therearetwopossibleexplanationsfortheformationofthesebrokencapsules:(i)THFcouldpermeatethecontinuousPPyoverlayer,causingthePScoretoswellwitharesultoffracturedpolypyrroleoverlayer;(ii)thepolypyrroleoverlayerisnotcompletelycontinuousandtheTHFdiffusesintothelatexcorethroughapatchypolypyrroleoverlayer.ForhighinitialfractionofPyCOOH,itispossiblethatthecontinuousshellsareporoussothattheypermitselectiveextractionofPS,butarerobustdespitealowerthickness(10and20nm,seeTable1).ItispossiblethathydrogenbondingbetweenadjacentCOOHgroupsimpartimprovedmechanicalresistanceto02004006008001000-100-80-60-40-200%.tWTemperature/°C-27.55%(PPy)-72.45%(PS)Fig.3.TGAthermogramofPS@PPyCOOH50microspheres.PPyCOOH75andPPyCOOH50shellscomparedtothemorebrittlePPyandPPyCOOH25capsules.3.1.2.FTIRFTIRspectra,inthe2000e1000cm1region,ofPSandPS@PPyCOOH75particlesareshowninFig.5.Thespectraaccountfortheexpectedstructureofthematerialssincepeaksduetopolystyrene(especiallyat1453and1494cm1)areobservedforbothPSandPS@PPyCOOHx,whileadditionalbandsduetotheconductingpolymershellareobservedforPS@PPyCOOHxonly.Onecannoteamongothersonebandat1560cm1duetothepoly-pyrroleconjugatedchainandonebandat1685cm1,characteristicofthecarboxylgroups.ThestericstabilizerPNVPisalsodetected(at1605cm1)showingthatitremainsadsorbedonthePSsurfaceevenaftercoatingbytheconductingpolymerlayer.Theintensityratioofthebandat1685cm1(duetothecarboxylgroups)tothebandsat1453and1494cm1(characteristicsofpolystyrene)hasbeenplottedasafunctionofthePyCOOHcomonomerfractioninthesynthesismedium(seeInsetinFig.5).Itisclear,fromthisplot,thattheintensityofthepeakat1685cm1increasesmonotonicallywiththeinitialfractionofPyCOOH.Therefore,thereisaprogressiveincorporationofthePyCOOHcomonomerinthecopolymershellwithincreasinginitialfraction.Fig.5.FTIRspectraofPSandPS@PPyCOOH75latexparticlesinthe1000e2000cm1region.InsetshowstheintensityratioICOOH/IPSofthecarboxylband(at1685cm1)tothePSbands(at1494and1453cm1)plottedagainstthePyCOOHfractioninthesynthesismedium.Table2ReportstheapparentsurfacechemicalcompositionofPNVP-stabilizedPS,PS@PPyandPS@PPyCOOHxlatexparticles.SamplesCNOClO/CPS@PNVP92350.05PS@PPy80.5211.66.541.350.081PS@PPyCOOH2580.9510.548.360.160.103PS@PPyCOOH5078.310.1211.600.15PS@PPyCOOH75789.5412.500.16A.Madanietal./Polymer51(2010)2825e283528293.1.3.XPSFig.6displayssurveyspectraofPNVP-stabilizedPS,PS@PPyandPS@PPyCOOH75latexparticles.ThemainpeaksareC1s,N1sandO1scenteredat285,400and532eV,respectively.ItisnoteworthythatN1sandO1srelativepeakintensitiesarefairlyhighbycomparisontothesamepeaksfromtheunderlyingPNVP-stabilizedPSduetothecontributionofthepolypyrroleshells,i.e.nitrogenfromthebackboneandoxygenfromthependantCOOHgroups.InsetofFig.6displaystheminorCl2ppeak(198eV)regionsforPS@PPy,PS@PPyCOOH25andPS@PPyCOOH75.Interestingly,foraninitialPyCOOHfeedratioaslowas25%,theCl2pgetsverynoisywithquasiabsenceofchloridesfromthePPyCOOH25shell.TheeffectisexacerbatedinthecaseofPS@PPyCOOH75.ThismostprobablyindicatesthatPPyCOOHxcopolymershellsareco-dopedbybothchloridesandcarboxylates.ForaPyCOOHfeedratiohigherthan25%,theconductivecopolymershellis“auto-doped”ataveryhighextentsincechloridesarenotdetectedbyXPS.Elsewhere,forpurePPyCOOHfilmsandpowders,Leeetal.[20]reported12.8and4.9%dopingbychlorides(Cl/Nratio),respectively.However,theseXPSresultswerenotsupportedbyanyCl2porsurveyspectra.Althoughtheyattributedsuchalowdopingtoconductivity,neverthelessitislikelythatthecarboxylatesactasco-dopants.Thisauto-dopingbycarboxylatesmightresultinlowconductivityforPS@PPyCOOHcomparedtoPS@PPysincePPyCOOHisabout4ordersofmagnitudelessconductivethanpurepolypyrrole(Table2).TheapproachreportedfortheanalysisofPMMA-coatedPPypowderswasusedtodeterminetherelativeproportionofPNVPontheuncoatedPSlatex[21].Onecanassumethat:CPS-PNVPzCPSþCPNVPwhereCPSL,CPS,andCPNVParetheatom%ofcarbonforPNVP-stabilizedPSlatex,PSlatexandPNVP,respectively.AccordingtothechemicalformulaofPNVP:CPNVP¼6NPNVPwhereNPNVPistheatom%ofNduetothePNVPcomponentinthePSlatex.ItfollowsthatCPNVPz20%andCPSz72%.PNVPandPSrepeatunitscontainsixandeightcarbonatoms,respectively.Thus,therelativeproportionofPNVPatthePSlatexsurfaceis%PNVP¼(20/6)/[(20/6)þ(72/8)]¼27%Fig.6.XPSsurveyscansofuncoatedPS,PS@PPyandPS@PPyCOOH75latexparticles.InsetsshowplotofO/Csurfaceatomicratioversustheinitial%ofPyCOOH,andhighresolutionCl2pregions.ThisrelativeproportionofPNVPatthesurfaceofthelatexparticlesisthesameasthevalueobtainedbyLascellesandArmes[5c,22]forthe