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1、14454J.Phys.Chem.B2005,109,14454-14460DispersionofSingle-WalledCarbonNanotubesofNarrowDiameterDistributionYongqiangTanandDanielE.Resasco*SchoolofChemical,BiologicalandMaterialsEngineering,UniVersityofOklahoma,100EastBoydStreet,Norman,Oklahoma73019ReceiVed:April29,2005;InFinalForm:May16,2005Thedi
2、spersibilityandbundledefoliationofsingle-walledcarbonnanotubes(SWNTs)ofsmalldiameter(<1nm)havebeenevaluatedonCoMoCATsampleswithnarrowdistributionofdiameters.AspreviouslyobservedbyphotoluminescenceandRamanspectroscopy,theCoMoCATsampleexhibitsauniquelynarrowdistributionof(n,m)structuresthatremains
3、unchangedafterdifferentdispersionconditions.Thisnarrowdistributionallowedustodevelopamethodforquantifyingthedispersabilityofthesamplesfromtheiropticalabsorptionspectraintermsoftworatios:theªresonanceratioºandtheªnormalizedwidth.ºTheformerisdefinedasthequotientoftheresonantbandareaanditsnonresona
4、ntbackground.Thelatterisdefinedastheratioofthewidthofthebandathalf-heighttothepeakheightonaspectrumthathasbeennormalizedat900nm,makingthisanintensiveproperty,ratherthanvaryingwiththepathlength.InthisstudyoftheCoMoCATsample,wehaveusedtheS22transitioncorrespondingtothe(6,5)nanotubetodothesecalcula
5、tions,whichisthemostabundantspecies.Thesetworatiosprovideaquantitativetooltocomparedifferentdispersionparameters(timeofsonication,degreeofcentrifugation,etc.)onthesametypeofsample.Fromthiscomparison,anoptimalprocedurethatmaximizesthespectralfeatureswasselected;thisprocedureallowedustocontrastvar
6、ioussurfactantsatdifferentpHvaluesandconcentrations.Severalsurfactantswereasgoodorevenbetterthantheonewehaveusedinpreviousstudies,dodecylbenesulfonicacidsodiumsalt(NaDDBS).Despitedifferencesintheirdispersionabilities,noneofthesurfactantsinvestigatedgeneratednewfeaturesintheabsorptionspectranorch
7、angedthedistributionofnanotubetypes,whichconfirmsthatthehighselectivityoftheCoMoCATsampleisintheoriginalsampleratherthancausedbyselectivesuspensionofspecific(n,m)nanotubes.Introductionthenoncovalentapproachhasbeenofparticula
