2010WILEY-VCHVerlagGmbH&Co.
KGaA,Weinheim4814www.
advmat.
dewww.
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comCOMMUNICATIONwileyonlinelibrary.
comAdv.
Mater.
2010,22,4814–4818ByYuhuaXue,HongxiaWang,YanZhao,LimingDai,LianfangFeng,XungaiWang,andTongLin*MagneticLiquidMarbles:A"Precise"MiniatureReactor[*]Dr.
Y.
Xue,Dr.
H.
Wang,Dr.
Y.
Zhao,Prof.
X.
Wang,Prof.
T.
LinCentreforMaterialandFibreInnovationDeakinUniversityGeelong,VIC3217(Australia)E-mail:tong.
lin@deakin.
edu.
auProf.
L.
DaiDepartmentofChemicalEngineeringCaseWesternReserveUniversityCleveland,Ohio44106(USA)Prof.
L.
FengStateKeyLaboratoryofChemicalEngineeringDepartmentofChemicalandBiologicalEngineeringZhejiangUniversityHangzhou310027(P.
R.
China)DOI:10.
1002/adma.
201001898Miniaturizedchemicalprocesseshavemanyadvantages,suchasreduceduseofchemicalreagentsandsolvents,preciselycontrolledreactionconditions,muchshortenedreactiontime,andtheabilitytointegrateintoadigitaldevice.
[1–4]Theyareveryusefulforhigh-throughputanalysesandpuricationsinchemicalandbiologicalprocesses,suchasdrugdiscovery,[5]DNAanalysis,[6,7]proteincrystallization,[8]andthesynthesisofmoleculesorparticles.
[9–11]Indeed,considerableeffortshavebeenmadetominiaturizechemicalprocessesusingvariousprinciples.
Forexample,oil/wateremulsionshavebeenusedtoperformchemicalreactionsinparallelinalargenumberofemulsiedtinydroplets.
[10]Microuidic"lab-on-a-chip"deviceshavebeendesignedtomanipulatechemicalprocesseswithinmicro-channelseitherincontinuousuidordisconnecteduidsegmentsseparatedbyanimmiscibleuidorgas.
[10,12]Althoughthechannel-basedmicro-reactorsshowgreatpoten-tialinhigh-throughputreactionandintegratabilitytoexternalanalysisfacilities,thereaction-specicdevicepreparations,thechannel-associatedcross-contaminations,andtheneedforexternalpumpstoactuatetheuidmotionmakethemneitheruniversalnorminiature.
Also,microuidicsishardtousetohandleasingledroplet.
Recently,freeaqueousdropletsinanimmiscibleuid(channel-freemicrouidics)[9]hasalsobeenproposedasanalternativestrategy,butcross-contaminationstillremainsaconcern.
Inlivingsystems,cellsarewell-knownasthebasicstructuralandfunctionalunits[13]thatmediatevariousbiochemicalreac-tions(e.
g.
,catabolismandanabolism)forsustainingthegrowthanddivisionofcellsandhencelivingsystems.
Althoughtheirstructurelooksverysimple,cellscommunicatewitheachotherinahighlyintelligentway,throughoutthewholelivingsystem.
Inthisregard,howtomimiclivingcells,bothinstructureandfunction,istheultimatechallengetowardthedevelopmentofarticialminiaturereactors.
Liquidmarbles,liquiddropsencapsulatedwithsolidpowderattheliquid–gasinterface,haverecentlybeenreportedasanewapproachtomanipulatingliquid,[14]whichcouldbeusedasminiaturereactors.
Theyarenon-wettingtoanysolidsur-facesandcouldbemanipulatedbyexternalforces,suchasgravity,[14]electrical,[15]andmagnetic,[16]dependingontheircomponents.
[14–19]However,mostliquidmarblesreportedsofarhavebeenbasedonaqueousliquid.
Althoughafewpapers[19]havereportedtheencapsulationoforganicliquidsintoliquidmarbles,theliquidswereconnedtothosehavingahighsur-facetension.
[19]Theformationofstableliquidmarblesfromawiderangeoforganicsolvents,especiallythosethathavealowsurfacetension,isimportantforchemicalreactions,butstillremainsachallenge.
Inthisstudy,wedemonstratetheincredibleabilityofauor-inateddecylpolyhedraloligomericsilsesquioxane(FD-POSS,structureshowninFigure1a)anditscombinationwithhydro-phobicmagneticnanoparticlestoactasencapsulatingagentstopreparestableliquidmarblesfrombothaqueoussolutionandorganicliquidswithasurfacetensionaslowas20.
1dynecm1,andthefeasibilityofusingthemagneticliquidmarblesasuni-versal"smart"miniaturereactors.
FD-POSSwassynthesizedbythereportedmethod[20,21]andaneFD-POSSpowderwaspreparedbyagrindingtechnique.
TheFD-POSS/Fe3O4nanoparticlecompositepowdersofdif-ferentratios(1:10to1:1,w/w)werepreparedbyco-dispersingtheneFD-POSSpowderwithhydrophobicFe3O4nanopar-ticlesinethanol.
AsshowninthephotographsinFigure1b,FD-POSSpowdersarewhiteandhaveacertaintransparencytovisiblelightbutarenotresponsivetoamagneticeld.
Inethanol,FD-POSSandFe3O4nanoparticleshadastrongafnity,andtheytendedtoaggregateintopowderswhichshowedasuperparamagneticproperty(SupportingInfor-mation).
TheopticalmicrographsinFigure1cindicatethatFD-POSSandFD-POSS/Fe3O4compositepowdersarelessthan70μm,andtheFD-POSSandFe3O4nanoparticlesformedarandomlyblendedcompositestructure.
Whenathinbedofthepowderswerecoatedonasolidsurface,thesurfacebecamehighlyrepellenttoliquids.
Water,dimethylsulfoxide(DMSO),toluene,hexadecane,andethanolallformedrounddropletsonthepowdercoatedsurfacewithoverallcontactanglesof171.
1°,166.
2°,155.
7°,154.
4°,and142.
8°,respectively(Figure1d).
Thepowderlayershowedstrongrepellencetootherorganicsolvents(SupportingInformation).
ThecompositepowdersinthestudiedFD-POSS/Fe3O4ratiorangeshowedaverysimilaruidrepellencytothepureFD-POSSgrains.
Liquidmarbleswerepreparedsimplybydroppingasmallvolumeofliquidontothepowdersurfaceandsubsequentlyshakingthedropletgentlysothatthepowderscoveredtheentiredropletsurface.
Theas-preparedpowders,bothFD-POSS4815www.
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com2010WILEY-VCHVerlagGmbH&Co.
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2010,22,4814–4818Severalwaterdropletswereaddedtotheopenedmarble(10μL)toformawater-in-oilbicomponentliquidmarble.
Oil-in-waterbicomponentliquidmarblescanalsobeproducedinasimilarway.
Thesebicomponentliquidmarblesshowtheabilitytopre-ventthecoreliquidfromrapidevaporation.
Todemonstratetheabilitytomediatechemicalreactions,weusedtwodifferentwaystoundertakeachemiluminescencereaction.
[22,23]Onemethodusedtwomagneticliquidmarblestocarrydifferentreactiveagents,oneforhydrogenperoxideandtheotherforbis(2,4,6-trichlorophenyl)oxalateanddye.
AsshowninFigure2f(toppanel),thetwoliquidmarbleswereactuatedunderamagneticeldtomovetogetherandtheythencoalescedintoalargerliquidmarble,initiatingthechemilumi-nescencereactionwhichcanbeprovenbyanimmediatelightemissionfromthecoalescedliquidmarble.
Anothermethodinvolvedusingabicomponentliquidmarbletohosttwocoredroplets,onefortheoxidantandtheotherfortheuorescer,inanimmiscibleuid.
Undergentlemovementactuatedbyamagnetbar,thetwocoredropletsjointedtogethertriggeringthechemiluminescencereaction.
TheimageinFigure2f(bottompanel)clearlyindicatesthelightemittingjustfromthecombinedcoredroplet.
Besidesthechemiluminescencereaction,otherchemicalreactionssuchasphotochemicalpolymerization,nanoparticlesynthesis,andanacid–basereactionhavealsobeentrialedandproventobesuccessful(SupportingInformation).
Oneimportantaspectforminiaturechemicalreactorsistheabilitytointegratewithpuricationandanalysisfacilities.
SincethemagneticliquidmarblescanbeopenedandclosedreversiblyandFD-POSS/Fe3O4composite,canencapsulatenotonlywaterbutalsoorganicsolventstoformstableliquidmarbles.
Figure2ashowsphotosofliquidmarblespreparedfromwater,DMSO,toluene,ethanol,andoctane(3μL).
Manyotherorganicsol-ventshavealsobeentestedsofarandthepowderswereabletoencapsulatealiquidofsurfacetensionaslowas20.
1dynescm1(SupportingInformation).
Theliquidmarblesareverystableandtheycanoatnotonlyonwaterbutalsoonauidoflowsurfacetension(Figure2b).
ThesuperparamagneticpropertyoftheFe3O4nanoparticlesimpartstheFD-POSS/Fe3O4powder-encapsulatedliquidmar-bleswithamagnetresponsiveability.
Asaresult,theliquidmarblescanbeactuatedtomoveindifferentdirections,oropenedandclosedreversibly,underamagneticeld.
Figure2cshowsmagnetopenedliquidmarblesfromdifferentliquids.
Theopenedliquidmarbleallowsittobecoveredwithanothertypeofhydrophobicmaterial.
Todemonstratethis,weusedpureFD-POSSpowdertocovertheopenedliquidsurfaceofamagneticliquidmarble,andthecoveredpartshowedadifferentcolortothemagneticpowdercoveredsurface.
Consequently,themotionofliquidcanbetracedeasily.
Figure2dillustratesthemotionofawhiteFD-POSS-stainedFD-POSS/Fe3O4hexa-decanemarbleunderamagneticeld.
Itcanbeclearlyseenthatthemarblerotatesonasolidsurface(toppanel),butshiftssidewaysonaliquidsurface(bottompanel).
Themagnetopenedliquidmarblealsoallowstheliquidtobetakenfromthemarbleorthemarbletobereplenishedwithotherliquids.
Figure2edemonstratestheadditionofcolorfulwaterdropletsintoamagnetopenedhexadecanemarble.
Figure1.
a)StructureofFD-POSS.
b)ProcesstomaketheFD-POSS/Fe3O4nanoparticlecomposite.
Theinsertimagetotherightshowsthesuspen-sionsofDP-POSSandtheFD-POSS/Fe3O4nanoparticlecompositepowdersinsolventandtheFD-POSS/Fe3O4underamagneticeld.
c)OpticalmicroscopyimagesofFD-POSSandFD-POSS/Fe3O4powders(FD-POSS:Fe3O4=1:1,w/w).
d)Water,dimethylsulfoxide(DMSO),toluene,hexade-cane,andethanoldropletsontheFD-POSS/Fe3O4powder-coatedsiliconsurface.
4816www.
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com2010WILEY-VCHVerlagGmbH&Co.
KGaA,WeinheimCOMMUNICATIONwileyonlinelibrary.
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Mater.
2010,22,4814–4818thatpushestheliquidoutofthepowderlayer.
Whetheraliquidmarblecanremainstableonasolidsurfaceornotisdeterminedbytheabilityofthenon-wettingpowderlayertopreventtheliquidbreakthrough(i.
e.
,breakthroughpressure,Pbreakthrough)andtheactualliquidpressuregeneratedbytheliquiddroplet(Pdroplet).
IfPbreakthroughPdroplet,theactualpressuregeneratedbytheliquiddropletisnotenoughtoforcethroughthepowderlayerhencetheliquidmarbleisstable.
WhenPdropletisclosetoPbreakthrough,itiseasyfortheliquidtobreakthepowderlayer,whichleadstobreakageoftheliquidmarble.
Basedonthecapillaryforceandtheliquidpressurethatforcesliquidtosagintothepowderypores(Figure3b,c),theratiobetweenthebreakthroughpressureandthemaximumliquidpressureformedbythedroplet(Pmaxdroplet=Dgl,whereρisthedensityoftheliquid,gistheconstantduetogravity,andl=γlv/ρgiscapillarylengthoftheliquid),PbreakthroughPmaxdroplet/,canbeestimatedas:PbreakthroughPmaxdroplet=A=H.
TH+T/(1)byamagneticeld,thereactionliquidcanberemovedeasilybyacapillarydeviceforfurtheranalysesordirectlytestedbyanopticalspectrometer(e.
g.
,UVanduorescentspectrom-eters).
Figure2galsoshowsthedirectpuricationofareac-tionproductthroughanarrowchromatographicaluminasheetpluggedintotheopenedliquidmarble.
Theabilityofahydrophobicpowdertorepelliquiduidismainlydeterminedbythesurfacechemistryandphysicaltopologyofthepowdermaterial,thesurfacetensionofaliquid,andthecontactmodebetweentheliquidandpowder.
TheFD-POSSmoleculecompriseseightuorinateddecylgroupswhichinclude136uorineatomssurroundingthePOSScage,makingthemoleculeextremelylowinsurfacefreeenergy.
Theroughsurfaceattributabletotheparticulatestructurefacilitatestheformationofanon-wettingpowderysurface.
[24–26]Inthestaticstate,theencapsulatingpowdersbetweenthedropletandthesolidsupport(Figure3a)receivethelargestliquidpressure.
Becauseofthenon-wettingfeature,theliquidonapowderyporouslayerreceivesanegativecapillarypressureFigure2.
a)DigitalgraphicimagesofliquidmarblesproducedfromdifferentliquidsandFD-POSSpowder(dropletsize3μL).
Foreasyobservation,asmallamountofdyewasaddedtotheliquidandtheexistenceofthedyehasnoinuenceonthestabilityoftheliquidmarbles.
b)Liquidmarblesoatingonwaterandhexadecanesurfaces(dropletsize3μL).
c)Magnetopenedliquidmarbles(dropletsize7μL).
d)Magnet-drivenmotionsofaFD-POSS-stainedFD-POSS/Fe3O4hexadecanemarbleonaglassslide(top)andwatersurface(bottom)(dropletsize7μL).
e)Magnetopenedhexa-decanemarbleswithdifferentnumbersofcoloredwaterdropletsadded(overalldropletsize10μL).
f)Achemiluminescencereactionthatoccursasaresultofcoalescingoftwomagneticliquidmarblesthatcontaindifferentreagents(top),andthesamechemiluminescencereactionhappeningwithinasingleliquidmarble(bottom)(dropletsize10μL).
g)Chromatographicanalysisofliquidintheopenedliquidmarble(dropletsize10μL).
Scalebar:1mm.
4817www.
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com2010WILEY-VCHVerlagGmbH&Co.
KGaA,WeinheimCOMMUNICATIONwileyonlinelibrary.
comAdv.
Mater.
2010,22,4814–4818liquids.
Magneticmanipulationenablestheliquidinthemarbletocommunicatewiththeoutsideenvironmentondemand,whichprovidesasimplewaytointegratewithportablepurica-tionandanalysisfacilities.
Allthesefeaturescouldleadtonewuniversal"lab-on-chip"reactorsystemswithexcellentintegrationabilitytoincorporatesamplefabrication,actuation,purication,andanalysisintoasingleelectronicchipfordiverseapplications.
ExperimentalSectionPreparationofFD-POSS/Fe3O4NanoparticleCompositePowders:(1H,1H,2H,2H-heptadecauorodecyl)8Si8O12(FD-POSS),synthesizedaccordingtotheliteraturemethod,[20]andhydrophobicFe3O4nanoparticles,preparedbyaliteraturemethod,[16]weredispersedin20mLofethanolandcontinuouslystirredfor24h.
Themixturewasthenisolatedfromthesolutionwithabarmagnetanddriedundervacuumat60°C.
PreparationandMagneticManipulationofLiquidMarbles:LiquidmarbleswerepreparedbydroppingliquiddropletsontoabedofFD-POSSorFD-POSS/Fe3O4nanoparticlegrains.
Upongentleshakingofthedroplet,thesolidpowdersbecamestucktothedropletsurfaceformingapowder-encapsulatedliquiddroplet(i.
e.
,liquidmarble).
Magneticmanipulationoftheliquidmarbleswasperformedusinganeodymiumcylindermagnet(diameter10mmandlength12mm).
Thedirectedmovementoftheliquidmarbleswasrecordedusingadigitalmicroscope(Dino-LiteAM313).
SupportingInformationSupportingInformationisavailablefromtheWileyOnlineLibraryorfromtheauthor.
H=2(1cosθ)lcapD(2√3D2ππ)(2)T=Blcapsin(2Rmin)R(2√3DB)(3)HandTaretherobustnessheightandangledeterminedbytheliquid–gassurfacetension(γlv),theparticleradius(R),theinterparticledistance(2D),andtheapparentcontactangleofliquidonthepowdermaterial(θ)(fordetailsseetheSupportingInformation).
ThedependencyofPbreakthroughPmaxdroplet/onthepar-ticleradiusandthehalfinter-particledistanceforthepowderarrangementisgiveninFigure3d(thecalculationontheotherparticlearrangementisgivenintheSupportingInformation).
ItisinterestingtonotethatamaximumPbreakthroughPmaxdroplet/ratiooccurswhenthepowderradiusisabout35μmandtheinter-powderdistanceissmall.
Basedontheactualpowderdimen-sionandsurfaceproperties,thePbreakthroughPmaxdroplet/Dforthreestudiedliquidsystemswascomputed(Figure3e).
Whenthisinter-powderdistanceislessthan160μm(D<80μm),thePbreakthroughPmaxdroplet/islargerthanunityeveniftheliquidsurfacetensionisverylow,suggestingtheformationofaverystableliquidmarble.
Insummary,wehavedemonstratedthepotentialofusinguorinatedPOSSandmagneticnanoparticlesasauniversalencapsulatingagenttoprepareliquidmarblesfromvariousFigure3.
a)Idealizedliquidmarblewithasinglelayerofpowderscoveringthedropletsurface.
b)Fluidsaggingintotwoparticlesandthedimen-sionsforcalculationofthebreakthroughpressure.
c)Onepowderarrangementusedforcalculationofbreakthroughpressure.
d)DependenciesofPbreakthroughPmax/dropletratioonRandDforoctane(θ=55°).
e)PbreakthroughPmax/dropletDdependencycalculatedbasedontheactualpowderdimensionforwater(θ=120°),hexadecane(θ=80°),andoctane.
4818www.
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dewww.
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com2010WILEY-VCHVerlagGmbH&Co.
KGaA,WeinheimCOMMUNICATIONwileyonlinelibrary.
comAdv.
Mater.
2010,22,4814–4818AcknowledgementsTheauthorsacknowledgethefundingsupportfromDeakinUniversityundertheAlfredDeakinPostdoctoralFellowshipschemeandStateKeyLaboratoryofChemicalEngineering(SKL-ChE-09D05).
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