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1、PublishedonWeb12/31/2005ShapeandAggregationControlofNanoparticles:NotShaken,NotStirredDanLiandRichardB.Kaner*ContributionfromtheDepartmentofChemistryandBiochemistry,DepartmentofMaterialsScienceandEngineering,andCaliforniaNanoSystemsInstitute,UniVersityofCaliforn
2、ia,LosAngeles,LosAngeles,California90095-1569ReceivedSeptember26,2005;E-mail:kaner@chem.ucla.eduAbstract:Theaggregationofnanoparticlesduringsynthesis,particularlytheeffectofmechanicalagitation,isinvestigatedfromaviewpointofnucleationusingaconjugatedpolymer,polya
3、niline,asanexample.Homogeneousnucleationofpolyanilineresultsinnanofibers,whileheterogeneousnucleationleadstogranularparticulates.Mechanicalagitation,whichisacommonmethodfordisruptingaggregates,insteaddramaticallytriggersaggregationduringthesyntheticprocessandfav
4、orstheformationofgranularparticulates.Correlatingtheshapeandaggregationofpolyanilinenanoparticleswiththemodeofnucleation,anewaggregationmechanismisproposedinwhichaggregationistriggeredbyheterogeneousnucleation.Themechanismmaybequitegeneralasindicatedbyexperiment
5、swithothermaterialssuchassilicananoparticles.Highlydispersiblepolyanilinenanofiberscannowbereproduciblypreparedfromaconventionalreactionsimplybynotmechanicallyagitatingthereactionandcarryingitoutatanelevatedtemperature.Thisworkmayprovetobeofgreatvalueinreproduci
6、blysynthesizingnanoparticleswithwell-controlledsizesandshapesandineffectivelypreventingaggregationinchemical,pharmaceutical,andmaterialsproductionprocesses.Introductionsynthesizingbulkpolyanilineisthechemicalpolymerizationofanilinewithanoxidant,ammoniumperoxydis
7、ulfate,inanAggregation,acommonyetcomplexphenomenonforsmallacidicaqueoussolution.Becausepolymerizationisanexother-particles,isproblematicintheproductionanduseofmanymicprocess,ithaslongbeenrecommendedthatthisreactionchemicalandpharmaceuticalproducts.Aggregationmak
8、esitbecarriedoutatlowtemperatureswithonereactantslowlyespeciallydifficulttoexplorethepropertiesandapplicationsaddedintotheotherundervigorousstirring.3Theresultingofna
