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13 tion.Therefore,theresultingplateletsexhibitaconductiv itylowerthanthatofamoreperfectNGPobtainedwiththe presentlyinventedproces. (5)Thepresentlyinventedproces,ifdesirable,allowsfora widerangeofchemicalspeciestomixwithaSupercritical fluidsothatdesirablespeciesmaycomeincontactwiththe resulting NGPs. For instance, a reactive species (e.g., oZone,oxygen,acidvapor,SOs,etc)maybemixedwithor dissolvedincarbondioxideforthepurposeofimpartinga desirablefunctionalgrouptoNGPswhilebeingformedor10 immediatelyaftertheirformation. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1ThethicknesofNGPspreparedwithorwithouta15 surfactantdissolvedinasupercriticalfluid.Thepressureves selcontainingNGPs,afterthefirst(initial)cycleofCO Supercriticalfluidintercalationandexfoliation,wasre-pres Surizedandde-pressurizedforanumberofcycles. FIG.2(A)AnMCMBsampleafterthefirstcycleofsuper criticalfluidintercalationandexfoliation;and(B)A TEM imageoftheresultingNGPsafterarepeatedcycle. 14 thedifusivityofwatermoleculesandthemobilityofother chemicalspeciesdissolvedinthewaterincrease. Hence,asapreferedembodiment,thepresentlyinvented processcomprises:(i)exposingagraphiticmaterialtoa supercriticalfluidatafirsttemperatureandafirstpressurefor afirstperiodoftimeinapressureveselandthen(i)rapidly depressurizingthefluidbydischargingpartofthefluidoutof theveselatafluidreleaseratesuficientforefectingexfo liationofthegraphiticmaterialtoobtainthedesiredNGP material.Presumably,thesupercriticalfluidinthepressure veselpenetratesintothespacesbetweengraphenelayersto form a tentatively intercalated graphite compound. With rapiddepresurization,thefluidintheinterstitialspaces quicklyexpandstopushapartneighboringgraphenelayers,a processcaleddelaminationorexfoliation.Thisexfoliation stepproducesNGPsthataretypicalythinnerthan10nmin thickness. As a first step, the starting material (e.g., natural flake graphiteparticles,MCMBs,orcarbonfibers)isplacedinside ahighpressurevesel.Theveselisthensealedofffromthe atmosphere.Thisisfollowedbyintroducinghigh-pressure CO intotheveselwithCO beingpressurizedtopreferably aboveapproximately1,070to10,000psig(7.4MPato69 MPa).Then,theveselisheatedtoatemperaturepreferably aboveabout40°C.,andmorepreferablyabove70°C.These conditionsdefineasupercriticalconditionofCO whereby theCO iscapableofpenetratingintointer-graphenespaces. US 8,696,938B2 FIG.3(A)Agraphitefibersampleafterfirstcycleof Supercriticalfluidintercalationandexfoliation(original graphitefibersofSubstantialysphericalcros-sectionwitha25 diameterof12umhavebeensplitintomanythiner,elon gate,flake-likefibrils);and(B)TheresultingNGPsaftera repeatedcycleexhibitalargelength-to-widthratio,inaddi Presurizingandheatingthegraphiticparticleswiththe tiontohavingaultra-highlength-to-thicknesratio(e.g., Supercriticalfluidmaybeaccomplishedbyanyconventional 1,000nm/0.34nm=3,000). DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 30 means.Forinstance,theveselmaybeheatedbyaheating jacketorelectricalheatingtapewrappedaroundthevesel. Ifachemicalspecies,suchasreactiveozonemolecules,is desired,itcanbeintroducedintothepressureveselbefore, during,oraftertheintendedsupercriticalfluidisintroduced. Ifthespeciesisinaliquidstate(e.g.,aSurfactantoracuring agentforaresin)orSolidstate(e.g.,aresin),itispreferably placedintothevesel(e.g.,mixedwiththestartinggraphitic material)priortosealingoffthevesel. Apreferedembodimentofthepresentinventionisapro35 cessthatinvolvesintercalatingandexfoliatingagraphitic materialwithasupercriticalfluidtoobtainNGPs.Optionaly, aSupercriticalfluidcancomprisethereinaSurfactant(or dispersingagent),acoatingagent(e.g.,amonomer,curing Theprocedurefurthercomprisescatastrophicalydepres agent,orresin),and/orareactivespecies(e.g.,OZone,oxygen,40 acidvapor,SOs,etc). Surizingthetentativelyintercalatedgraphitebyreleasingthe fluidoutoftheveselatahighrate.Duringcatastrophic depresurization,theSupercriticalfluidrapidlyexpandsto exfoliatethegraphitelayers.Thedepresurizationstepcom prisesimmediatelydepressurizingtheveseldowntoacon siderablylowerpresure,preferablyambientpresure.This maybeaccomplishedinatimeperiodofbetweenabout5and 30seconds,andpreferably15seconds.Specificaly,thismay beaccomplishedbydepressurizingthepressureveselata rateofbetweenabout0.1and5.0mililiterspersecond,and preferably3.0mililiterspersecond.Thepressuredecrease maybeaccomplishedbyopeningaveselvalvetotheatmo Ifasubstanceisheatedaboveacriticaltemperature(Tc) andpressurizedaboveacriticalpressure(Pc),itbecomesa supercriticalfluid.Supercriticalfluidsareknowntoprovide convenientmeanstoachieveSolvatingproperties,whichhave45 bothgasandliquidcharacteristicswithoutactualychanging thechemicalstructureofasubstance.Withapropercontrolof pressureandtemperature,severalphysicochemicalproper ties(e.g.,density,difusivity,dielectricconstant,Viscosity, andSurfacefreenergy)ofthisSubstancecanbevariedtoa50 significantextent.Inparticular,underSupercriticalfluidcon ditions,afluidcanreadilydifuseintotheinternalstructureof sphere.Asimmediatedepresurizationocurs,thegraphite asolidmaterial;e.g.,inter-graphenespacesinagraphitic material. Asanexample,carbondioxidemayexistasaSupercritical55 fluidhavingpropertiesofbothaliquidandagaswhenabove itscriticaltemperature(>31°C.)andcriticalpressure(>7.4 MPa).Undersupercriticalconditions,COexhibitsbotha Supercriticalfluidatasecondtemperatureandasecondpres gaseousproperty,beingabletopenetratethroughmanymate Sureforasecondperiodoftimeinapressurevesel(prefer ablythesamevesel)andthen(b)rapidlyde-presurizingthe fluidatafluidreleaseratesuficientforefectingfurther exfoliationoftheNGPmaterial.Thesecondtemperaturemay bediferentfromorthesameasthefirsttemperatureandthe rialsandaliquidproperty,beingabletodisolvemanymate60 rials.AlthoughCOisapreferedmedium,theSupercritical fluidmaybeselectedfromothersuitablespecies,suchas water,hydrogenperoxide,oZone,wateroxidation,methane, ethane,ethylene,oramixturethereof.Thesupercriticalpoint secondpressuremaybediferentfromorthesameasthefirst ofwatercomprisesatemperatureofatleastabout374°C.and65 apressureofatleastabout2.1MPa.Atoraboutthesuper criticalpoint,thedensityandViscosityofwaterdecreasesand presure.Itwasobservedthatahigherpressureforagiven presurizationtimetendedtoresultinamoreefectiveexfo liation,asevidencedbyareducedaverageNGPthicknes. layersaredelaminatedapartfromoneanother. The process may further comprise a procedure that involvesesentialyrepeatingthepresurization/heatingstep andthedepresurizationstepforatleastanothercycle.The repeatingcycleincludes(a)SubjectingtheNGPmaterialtoaPDF Image | SCO2 Producing Nanographine Platelets
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