loadingArticlepubs.acs.org/LangmuirMagneticFieldAligned对齐的丆使成一直线AssemblyofNonmagneticCompositeDumbbellsinNanoparticle-BasedAqueousFerro铁磁流体?uid
HayatoTakahashi,DaisukeNagao,*KanakoWatanabe,HaruyukiIshii,andMikioKonno*
DepartmentofChemicalEngineering,TohokuUniversity,6-6-07Aoba,Aramaki-azaAoba-ku,Sendai,980-8579Japan
*
SSupportingInformation利用外磁场作用于铁磁流体丆使单分散非磁性非对称复合材料哑铃颗粒组装成一直线ABSTRACT:Monodisperse,nonmagnetic,asymmetricalcom-positedumbbellsinasuspensionofmagnetic非对称的nanoparticles(ferro??uid)were使成一直线alignedbyapplicationofwereeldtopreparedtheferroby?uid.two-stepTheasymmetricalanexternalmagneticsoap-freeemulsioncompositepolymerizationdumbbells两步无皂乳液聚合制备非对称复合哑铃材料。consistingofthe?rstpolymerizationtocoatsphericalsilica在二氧化硅球表面包覆coreswithcross-linkedpoly(methylmethacrylate)(PMMA)交联的PMMA壳丆然后长出PS球。shellandthesecondpolymerizationtoprotrudeapolystyrene(PSt)lobefromthecore?shellparticles.突出Achainstructureof采用外磁场控制取向丆得到nonmagnetic耳垂dumbbellsorientedtotheappliedmagnetic?eld链状结构。wasobservedatnanoparticlecontentof2.0vol%and?eldstrengths?alsoeldatconductedstrengthshigherthantohigher1.0examinethanmT.50AindependenceV/mm.similarParallelchainstructure平行oftheandofthedumbbellswasobservedunderapplicationofalternating交变电场electricelectricorthogonally正交地andmagneticcombinedapplicationsapplicationsasofoperationaltheelectricandfactorsmagneticinthe?eldsdumbbellwereassembling.Dumbbellchainssti?er独立性thanthoseinasingleapplicationofexternal?eldwere作用参数丆工作参数formedintheparallelcombinedapplicationofelectricandmagnetic硬的?elds.Theorthogonalcombinationofthedi?erentapplied?eldscouldformamagneticallyalignedchainstructureofthenonmagneticdumbbellsorientedtotheelectric?eld.Thepresentworkexperimentallyindicatedthattheemploymentofinversemagnetorheologicale?ectfor使适应nonmagnetic,anisotropicparticlescanbeausefulmethodforthesimultaneous同时的丆同步controlsovertheorientation磁流变andthepositonofanisotropicparticlesintheirassembling.■INTRODUCTION
interactionsdependingontherelativepermeabilitybetweenAvarietyofanisotropicparticleswithdi?erentshapeshavenonmagneticparticlesandmediumandtherelativepositionsbeensynthesizedbecauseoftheirintrinsicbetweentheparticles.Inversemagnetorheologicale?ectwas1?4propertiesthatarenotobservedforisotropicparticles.directlyobservedwithanopticalmicroscopetocon?rmthata?Control7overassembledstructuresoftheanisotropicparticles5isanimportantissuechainstructureofmicron-sized,monodispersepolystyrenetodeveloppractical“bottom-up”processesforapplicationofspheresdispersedinakerosene-basedferro?uidwasformedtheintrinsicpropertiestooptical,electronic,andmagneticparalleltoamagnetic?eldappliedtotheferrofuild.16Thedevices.Sinceanisotropicparticlesexhibitphasebehaviorricherinversee?ectwasalsoemployedtoformlinearlyassembledthansphericalparticles,8,9external?eldssuchaselectricandstructureofcellsinaferrofuild.17fordevelopinganewmethodmagnetic?eldshavebeenappliedtoassisttheorientationandofcellmanipulation.Avarietyofassembledstructuresthepositionofanisotropiccomposedofbidisperseortridispersesphereswererecently14,27,30,31particlesinthefabricationofassembledstructures.10?Dipole?dipoleinteractiondemonstratedinducedamongparticlesundertheexternal?eldscanbe18,24inanaqueousferro?uidunderanappliedmagnetic?eld.tunedbyanumberofparticlefactorssuchasparticleThepresentworkappliedtheinversemagnetorheologicaldimension,shape,composition,andpermittivity/magnetice?ecttoaferrofuildinwhichanisotropic,nonmagneticparticlespermeabilityoftheparticles.
weredispersed.MonodisperseasymmetricaldumbbellswereThedipole?dipoleinteractioncanalsobevariedwithusedasanisotropicbuildingblocksdispersedintheferro?uidofelectric/magneticpropertiesofthecontinuousmediadispers-magneticingtheparticles.15Aninterestingexampleoftuningthe?dipole?dipoleinteractionbythemediumpropertiesisinverseanisotropic,ndanewnanoparticles.Thepurposeofthepresentworkistononmagneticmethodforparticlesalignedassembledorientedtostructureaspeci?ofcferro?uidsinwhichnonmagneticparticlesweredispersedinadirection.Sincesyntheticprocessesforthenonmagneticmixtureofmagneticnanoparticlesandaliquidmedium.25,26particlesdonotneedincorporationofmagneticcomponents
Thenonmagneticparticlesdispersedintheferrofuildexhibitadiamagneticresponsetoinducemomentsantiparalleltoanappliedmagnetic?eld.29ThediamagneticresponseundertheReceived:February26,2015Revised:April28,2015
magnetic?eldcausesattractiveorrepulsiveparticle?particle
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DOI:Langmuir10.1021/acs.langmuir.5b00737XXXX,XXX,XXX?XXX
LangmuirArticleFigure1.Nonmagneticdumbbellsandmagneticnanoparticlesusedintheassemblingprocess.TEMimagesofdumbbellswithlowandhighmagnimeasured?cationsarepresentedandacorrespondingin(d)andSEM(e),respectively.
imageareshownin(a)?(c),respectively.TEMimageofmagneticnanoparticlesandtheirsizedistributionintotheparticlesandtheyaregenerallysimplerthanthoseforofnewbottom-upprocessestocreateself-assembledthemagneticparticles,nonmagneticparticleswithlowpolydispersitycanbesynthesizedmoreeasilythanmagneticparticles.Thesuperiorityofnonmagneticparticlesexpectswell-orderedassembledstructureoftheanisotropicparticles.Anotheradvantageofemployingnonmagnetic,anisotropic■
architecturescomposedofanisotropicbuildingblocks.
EXPERIMENTALSECTION
Materials.Tetraethylorthosilicate(TEOS,95%),aqueousammo-particlesasbuildingblocksisnoincorporationoflight-niaabsorbingmaterialsintoassembledanisotropicparticles,98%),solutionstyrenep-styrenesulfonate(25%),ethanol(99.5%),methylmethacrylate(MMA,becausemagneticnanoparticles(i.e.,magnetitenanoparticlesinthepresentwork)intheassembledarchitecturecanbe95%),Pureand(St,hydrochloric99%),sodium(NaSS),acidchloridepotassium(HCl,(99.5%),persulfate(KPS,95%),2M)wereiron(III)purchasedchloridefrom(FeClWako3,selectivelydissolvedwithanacidicsolution.NoincorporationthoxysilaneChemicalIndustries(Osaka,Japan).Methacryloxypropyltrime-oflight-absorbingmaterialsinthearchitectureofanisotropicobtainedparticleso?erstheirhighpotentialsofopticalapplications.Chemicalfrom(MPTMS)Shin-Etsuandiron(II)chloride(FeCl2,99.9%)wereTherefore,we?rstpreparednonmagneticdumbbellscomposedMMAofsilica,poly(methylmethacrylate)(PMMA)andpolystyreneTheandLaboratoryStwereremoved(Saitama,ChemicalbeforeJapan),(Tokyo,userespectively.Japan)byinhibitorremovalTheandinhibitorsKojundoof(PSt)bytwo-stepsoap-freeemulsionpolymerization.19AnParticleotherchemicalsSynthesis.werecolumns.Asymmetricalusedasreceived.
compositedumbbellswereexternalmagnetic?eldwasappliedtothenonmagneticprepareddumbbellstostudythecontrollabilityovertheirorientationparticlesbytwo-stepsoap-freeemulsionpolymerizationwithsilicaandassembledstructureintheferro?uid.Then,anexternalsizesynthesizedof890usednmassphericalandacoecores.19?cientTheofsilicavariationparticles(withanaverageelectric?eldwasappliedtoexploreanotheroperationalfactorcross-linkedinforcontrolsovertheorientationofnonmagneticdumbbellsinthePMMAStoerCV)of1.3%werebbymethod.theThesilicaparticleswerecoatedwiththe?uid.Finally,combinedapplicationsofelectricandwithsilicamagnetic?elds23werecarriedouttoexamineindependence°nitrogencoresforand30MPTMSfollowingmin,andwereaddedpolymerization.towaterthatAsuspensionwasbubbledofofthetwodi?erentapplicationsasoperationalfactorsintheandC.Afterdumbbellassemblingprocess.
conductedfurther30stirredminstirring,MMAtheandmixedNaSSsuspensionwereaddedwastostirredthemixtureat35Thepresentworkproposesforthe?rsttimethattheinversesilicaat65°Cforfor2h.2hThewithpolymerizationKPSinitiator.ofTheMMAconcentrationsandNaSSwasmagnetorheologicale?ectisausefulphenomenonfornon-0.2coresM,cores,1.0MPTMS,mM,andMMA,2.0mM,NaSS,respectively.andKPSThewere0.15vol%,2.0mM,ofmagnetic,anisotropicparticlestobeassembledsimultaneouslyredispersedwerewashedthreetimesiniterativecentrifugePMMA-coatedprocessessilicacontrollingtheirorientationandlocation.NoincorporationofhighlydielectricmaterialsisrequiredforanisotropicbuildingtheProtrusionintoofdeionizedaPStlobewater.
andfromtheblocksinthepresentmethodwhereasasymmetricincorpo-corefollowingrationoftitaniacoresintobuildingblocksofdumbbellswasand?shellparticlespolymerizationandNaClofSt.AsuspensionPMMAshellofwasthesilicaperformed?PMMAbyrequiredinourprevious21toinduceinteractionbetweenpolymerizationStmonomerspeci?cpartsofthedumbbells.Thehighapplicabilitytoandnonmagnetic,anisotropicparticlesisessentialfordevelopment
andmore.TheofconcentrationsStwaswasaddedwereconductedtothebubbledmixture.withAfternitrogen2hstirring,for30min,theofcorewith?shellKPSinitiatorparticles,atstyrene,65°CforNaCl,7hTheKPSparticleswere0.11formedvol%,were0.2M,washed1.0mM,byanditerative2.0mM,centrifugesrespectively.and
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DOI:Langmuir10.1021/acs.langmuir.5b00737XXXX,XXX,XXX?XXX
LangmuirArticleFigure2.Nonmagneticdumbbellsobservedintheferro?uid(upperrow)andinwater(lowerrow).Concentrationsofdumbbellsandmagneticnanoparticlesmagnetic?eldinapplicationtheferro?uidat1.0weremT.
0.1and2.0vol%,respectively.Snapshotsweretakenundernomagnetic?eldsand3?120safterinitiationofredispersedwereobservedintowithdeionized?eldemissionwater.Thetransmissioncompositeelectrondumbbellsmicroscopyobtained1a.ThePStlobesinthedumbbellshadsizesalmostthesameas(FE-TEM;thoseforsilica?PMMAcore?shellpartsjointedtothePStMagneticHitachi,nanoparticlesHD-2700).
tobeusedforferro?uidpreparationwerelobe,althoughthesurfaceofPStlobeswassmootherthanthesynthesizedwithamodi?edMassartmethod.20core?shellpartsasshowninFigure1bandc.Figure1dshowssolutionthemagneticnanoparticlespreparedinthemodi?edMassartwithNHdissolvingsolutionFe2+andstirredandFe3+forat1ah.molarTheblackrationBrie?suspensionofy,1:2ahydrochloricwasformedmixedmethod.Thenanoparticleshadanaveragesizeof10nm,muchwas3smallerthanthesizesofnonmagneticdumbbells(seeFiguredissolvingcentrifugedasilaneandredispersedcouplingagenttowater.ofMPTMSThen,anwasethanolicaddedsolutiontothe1e),andtheyexhibitedasaturationmagnetizationof65emu/g.redispersedstabilizertosuspension.improvecolloidalTheMPTMSstabilitymoleculesofthemagneticwereusednanoparticles.asastericTheinversemagnetorheologicale?ectwascon?rmedbyThecomparingdumbbellmotionsinthepresenceandabsenceofprocesssuspensionofcentrifugewasreactedandredispersionfor1hunderwascarriedstirring,outandagainthetocombinedremovemagneticnanoparticles.ThesnapshotsofthenonmagneticMPTMSdumbbellssurface.ThemoleculescolloidalnotstabilitytobeoftheintroducedMPTMS-modionto?theednanoparticlesnanoparticle?wasofeldFigurestrengthdispersedintheferro?uidandinwateratamagnetic2,respectively.of1.0mTareTheshownconcentrationsintheupperofanddumbbellslowerrowsandinSupportingcon?rmedbyInformationmeasurementFigurewithdynamicS1,showinglightthatscatteringnoaggregatesasshownmagneticnanoparticlesfortheuppersnapshotswere0.1andlarger2.0vol%,respectively.ThelocationofthesilicaspheresintheParticlethan1Assembling.μmweredispersedThenonmagneticintheferro?compositeuid.
dumbbellsintheasymmetricdumbbellscouldbeidenti?edwiththeoptical×microscopeimagesduetodi?erenceintherefractiveindices.microscope1ferromm?uidrectangularunderexternalcross?eldssection,wereVITROobservedinacapillarycell(0.1AnexampleofopticalimagefordistinctionbetweenthePStcapillarycell,(Keyence,two50μVHX-2000).mdiametercopperTointroduceCOM)wires(99.99%,electrodeswithaNIRACO)intodigitalthelobeandthePMMA-coatedsilicawaspresentedinFigureS2ofweretheSupportingInformation.ThelobeofPStwitharefractive?threadedthroughalongthesidecapillarywalls.indexhigherthanPMMAexhibithighcontrastinwateronthedumbbells,lledwiththeaqueousferro?uidofnonmagneticThecapillarycompositewasmicroscopeobservation.Also,thePStlobeseemedyellowishin?theopticalmicroscopebecausetheyformedinpolymerizationgeneratoreldwasappliedandthebyendsofcapillaryweresealedwithglue.TheACBloc,(GWINTEK,connectingSFG-2004)theandcopperampli?erwires(NFtoafunctionwithpotassiumpersulfateinitiator.IntheupperrowofFigure2measuredHSA4011).withadigitalTheelectricoscilloscope?eld(GWINTEK,strength(peakCircuitGDS-1062A).topeak)DesignwasAn(alsoseeFigureS3),thelongaxesofnonmagneticdumbbellsapplicationintheferro?uidwerealignedtotheappliedmagnetic?eldandmagnet.Strengthofexternalofamagneticmagnetic?eld?eldappliedwasconductedtothecapillarywithacellferritewastheywereassembledtoformachainstructurewithinaminutemeasuredafterinitiationofthe?eldapplication(seeMovie1observationwithofanonmagneticteslameterdumbbells.(KANETEC,TheTM-701)concentrationsbeforetheof(a5b00737_si_002.avi)intheSupportingInformation),where-dumbbellsasrandomdispersionofthedumbbellswasmaintainedinthe0.1vol%andand2.0magneticvol%,respectively,nanoparticlestoinacquiretheferroclear?uidimageswereofsettheirtoabsenceassembleddumbbellswerestructurenotwithclearthesu?cientlymicroscope.toidentifySincethesomeorientationimagesofof?ofmagneticnanoparticlesundertheappliedmagneticdumbbellsdumbbellseldasshownatmagneticinthelowernanoparticlerowofconcentrationsFigure2.Observationlowerthanofareaonanonopticalpaper,microscopeschematicscreendrawingsarepresentedfordumbbellsintheinSupportingaspeci?c1.0vol%wassimilartotheoneshowninthelowersnapshotsInformation(seeFiguresS3?S7).
ofFigure2.TheinteractionforcebetweentwononmagneticspheresinthepresenceofmagneticnanoparticlesisattractiveRESULTSANDDISCUSSION
whenanonmagneticsphereislocatednexttoanotherspherewiththecenter-to-centerlineparalleltothe?eld.15SincetheFigure■
1showsnonmagneticcompositedumbbellsanddipolemomentsofthenonmagneticspheresinducedbymagneticnanoparticlesusedfortheobservationofinverseapplicationofmagnetic?eldisofthe?rstorderwithrespecttomagnetorheologicale?ect.Monodispersedumbbellparticlesthevolumeofspheres,16amainreasonforthechainstructureincorporatingasilicacorecouldbepreparedasshowninFigure
ofdumbbellsinFigure2isattractivedipolarinteraction
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DOI:Langmuir10.1021/acs.langmuir.5b00737XXXX,XXX,XXX?XXX
LangmuirArticleFigure(b),and3.5.0Nonmagnetic(c)mT.SeedumbbellsFigure2observedfortheconcentrationsintheferro?uidof1particles.
minafterinitiationofmagnetic?eldapplicationatdi?erentstrengthsof1.0(a),2.5Figureand1004.(c)NonmagneticV/mm.SeedumbbellsFigure2forobservedtheconcentrationsintheferro?uidof1particles.
minafterinitiationofelectric?eldapplicationatdi?erentstrengthsof25(a),50(b)Figure?andeld1at5.(b25Chain?(b),d)min50structures(c)afterandinitiation100ofnonmagnetic(d)ofV/mmtheadditionalwasdumbbellsappliedformedelectric1min?elds.afterintheSeeinitiationferro?uidFigureofunder2theformagnetictheparalleltheconcentrations?eldapplicationsapplicationofofparticles.
at2.5electricmT.andSnapshotsmagneticwere?elds.takenElectric0(a)Figure6.Chainstructuresofnonmagneticdumbbellsformedintheferro?uidundertheorthogonalapplicationsofelectricandmagnetic?elds.Electrictaken0?(a)eldandat251(b),(b?50d)(c)minandafter100initiation(d)V/mmofthewasadditionalapplied1electricminafter?elds.initiationSeeFigureofthe2magneticfortheconcentrations?eldapplicationofatparticles.
2.5mT.Thesnapshotswerestronglyinducedbetweendumbbellswithlongaxesorientedtoferro?uid.Figure4showssnapshotsofthedumbbellsobservedthe?eld.
1minafterinitiationof1MHzelectric?eldapplicationsat25,Thechainstructureformedintheferro?uidwasalso50,and100V/mm(alsoseeFigureS5).Theapplicationsatobservedatmagnetic?eldstrengthshigherthan1.0mT.Figure3showssnapshotsofthedumbbellsobserved1minafter?chaineldstrengthsstructuresof3250similarand100toV/mmthoseobservedcouldformin?Figureeld-oriented3b.Itinitiationof?eldapplicationsatdi?erentstrengthsof1.0,2.5,seemedthatdumbbellchainsobservedand5.0mT.Long-axisorienteddumbbellchainstructure28at100V/mmweresti?erthanthoseat50V/mm(compareMovie2slightlylongerthanthatformedat1.0mTwasobservedatthe(la5b00737_si_003.avi)for50V/mmandMovie3highstrengthsof2.5and5.0mT(alsoseeFigureS4),showing(la5b00737_si_004.avi)for100V/mm).Theresponsesofthattheapplicationofmagnetic?eldcanbeanoperationaldumbbellstotheappliedelectric?eldinFigure4were,factorfororientationofthedumbbellsintheirassemblinghowever,slightlyweakenedbytheadditionofmagneticprocess.Thehighmagnetic?eldof5.0mT,however,causednanoparticlestotheaqueousmediumprobablybecausepartialaggregationsofthedumbbellsintheferro?uidasshownpermittivityandviscosityofthemediumweredecreasedandinFigure3c.
increased,respectively,bythenanoparticleaddition.
ControllabilityonchainformationwithanexternalelectricAccordingtotheobservationspresentedabove,thetwo?eldwasalsoexaminedforthenonmagneticdumbbellsinthe
di?erent?eldsofmagneticandelectric?eldswereparallel
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DOI:Langmuir10.1021/acs.langmuir.5b00737XXXX,XXX,XXX?XXX