荧光超疏水(3)

Thisjournalis?TheRoyalSocietyofChemistry2015Fig.3

(a)Fluorescenceemissionspectraofthepolypyrene?lm(lexexcitation?

408nm,red)andFPSH?lm(lex?408nm,green).Inset:thespectraofthepolypyrene(lem?498.5nm,black)andFPSH(lem?490.5nm)?lms.(b)Excitation(lem?blue)451.5ofnm,polypyreneblack)anddissolved?uores-cenceemissionspectra(lex?349nm,inDMF.(c)Fluorescencephotographofthepolypyrene?lm(blue-green?uorescence,left)andpolypyrenedissolvedinDMF(blue?uores-cence,right),under365nmUVlight.(d)Photographofrandomlydistributedwaterdroplets(8mL)ontheyellowFPSH?lm(top).Thesewaterdropletsshowanearlysphericalshape.Under365nmUVlight,theFPSH?lmemitsstrongblue-green?uorescencelight(bottom),andthewaterdropletsstillretaintheirsphericalshape.solutiontosolidstate,andasignicantred-shiofabout47nmintheiruorescencespectracanbedetected.Ingeneral,theexcimeremissionbandsofpyrenespeciesarelocatedabove460nm.27Theuorescenceemissioncenteredat498.5nmmayoriginatefromtheexcimerformsinthesolidpolypyrenelm.21,22,27Furthermore,suchanexcimeremissioncanbereadilyrealizedwhentheelectrodepositionchargeismorethan105.3mCcmà2(Fig.S5andS6?).

Thestrongexcimeremissioninapolypyrenelmisauniquephenomenon.Duringtheelectrochemicalprocess,theoligo-pyrenesweregraduallydepositedontheelectrode.Theolig-omeraggregationwithintermolecularoverlappingpyreneunitsmayresultinintermolecularp–p*stackinginteractions27formingtheexcimerinthesolidpolypyrenelm.TheX-raydi?raction(XRD)patternofthepolypyrenelmpresentsaverybroaddi?ractionpeak(centeredat2q?23.5??)thatmighthaveoriginatedfromstackedpyreneunits.27dFurthermore,agoodprogressionofdi?ractionpeaksat2qanglesof5.7??,11.4??,and16.6??conrmsthattheoligopyrenelmalsocontainsseveralmicrocrystallinestructures(seeESIsectionandFig.S7a?(bottom)).21,22,27Inaddition,themicro/nanometer-scaleporousdrapestructureofthepolypyrenelmfacilitatesthereductionoftheuorescencequenching.27Theseuniquestructuralchar-acteristicsmayleadtoastrongexcimeremissioninsolidpolypyrenelms.

Aerdepositingthesilicalayer,theresultingFPSHlmperfectlyinheritedtheuorescencepropertiesofthepolypyrenelm.Astronguorescenceemissioncenteredat490.5

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(Fig.3a(green))uponexcitationat408nm(theinsetofFig.3a(red))wasreadilydetected.Aslightblue-shiofabout8nmwasobserved,probablyduetothefactthattheincorporationofthesilicalayerintotheaggregateoligopyreneleadstoanalterationofthemicro-environmentaroundtheoligopyreneexcimers,involvingintermoleculardistanceandpressure.21,22,27Notably,theshapeandthemaximumpositionoftheexcimeremissionbandoftheFPSHlmwerenotobviouslya?ectedbytheexci-tationwavelengthsfrom350to490nm(Fig.S8andS9?).ThismeansthattheuorescenceemissionspectraoftheFPSHlmaresignicantlydi?erentfromthoseofthepolypyrene/DMFsolution,evenifexcitingthemwiththesameexcitationwave-length,suchas350and408nm.Nevertheless,theFPSHlmhasanabsoluteuorescencequantumyieldofabout9.1%(excitationat408nm)(Fig.S10?).Fig.3dshowstheoriginalanduorescencephotographsofthesuperhydrophobicFPSHcoating.Waterdroplets(8mL)placedonsuchaluminousFPSHlmsurface(under365nmlight)clearlyexhibitsanearlysphericalshape.Therefore,theFPSHlmnotonlyhasgoodsuperhydrophobicself-cleaningproperties,butalsopresentsexcellentuorescencecharacteristics.

Robustuorescenceandsuperhydrophobicity

ThestabilityofFPSHlmsathightemperaturewasinvestigatedtosupporttheirpracticalapplication.AsshowninFig.4a,theuorescenceintensityofthecoatingonly??slightlydecreaseswithincreaseinthetemperaturefrom10Cto90??C.Nevertheless,theWCAandSAofthelmremainedalmostunchanged,evenaerannealingthesampleattemperaturesupto200??Cfor1hinair(Fig.4b).Interestingly,theFPSHlmstillexhibitedstronguorescenceaerannealingat200??C(insetinFig.4b(le)).TheseresultsindicatethattheFPSHlmpossessesanexcellentthermalstability.TheFPSHlmalsoexhibitsastrongrepel-lencetowater(WCA>150??)foranacidorabasedroplet,asevidencedbymeasuringtheCAandSAofthewaterdropletswithpHvaluesofabout1and13(Fig.4banditsinset(right)).Inmanypracticalapplications,superhydrophobiccoatingsoensu?erfromawater-dropletimpactduringwhichawettingpressure(Pwetting)isgenerated.Atthattime,thechangeofthewettingstateoftheroughsurfacedependsonthebalancebetweenthePwettingandthecapillarypressure(Pcapillary)gener-atedwithinthesurfacetexture.28,29IfPwettingis>Pcapillary,itleadstothewater-dropletwettingthecoatingsurface.Thus,forpracticalapplications,theinvestigationofwater-dropletimpingementonsuperhydrophobicsurfaceshasrecentlyreceivedincreasingattention.28,29Inourwork,water-dropletimpactexperimentswereperformed.Waterdroplets(20mL,radiusofabout1.68mm)wereusedtoimpacttheFPSHlmatthevelocity(V0)of1.08msà1(fallheightof6cm).Theimpingementprocessofwaterdropletsonthesurfacewascapturedbyahigh-speedcamera(Fig.4c).ThethirdimageinFig.4cshowsthatalargeroundhatwithanundulatedrimwasformedontheFPSHlmsurfaceatthemomentofthehigh-velocityimpact;aerthat,thewaterdropletreboundedwithoutanypinnedsatellitedropletleavingthesurface.Thisresultindicatesthatthecoatingshowedtherobust

2090|J.Mater.Chem.C,2015,3,2086–2092Fig.4(a)FluorescenceintensityoftheFPSH?lmatdi?erent

temperaturesrangingfrom10to90??C(lex?408nm).Inset:corre-spondingemissionspectra.(b)Anti-wettingstabilityofaFPSH?lm

evaluatedbymeasuringtheWCAandSAafterannealingat100and200??Cfor1hinair,andmeasuringtheCAandSAofwaterdropletswithpH1and13.Insets:?uorescencephotographofthe?lmafterannealingat200??C(left),andphotographofthe?lmwithanaciddroplet(red,8mLH2SO4solutionofmethylorangewithpH$1)andabasedroplet(blue,8mLNaOHsolutionofthymolphthaleinwithpH$13)(right).(c)Sequentialphotographsofa20mLwaterdropletbouncingo?theFPSH?lmatanimpactvelocityof1.08msà1.Thescalebaris4mm.(d)Photographsofthelettersandbladecastingtheirshadowsontothe?lms.(e)The?uorescencemicroscopepictureoftheFPSH?lmexcitedbythebluelight.Thescalebaris100mm.(f)The?uorescencemicroscopepictureoftheFPSH?lmcoveredwithamicro-grid.Thescalebaris100mm.

superhydrophobicityduringtheimpactofwaterdroplets.Infact,duringthewater-dropletimpact,thewettingpressurePwettingcomprisestwocomponents:thewaterhammerpressure(PWH)atthecontactstageandtheincompressibledynamicpressure(PD)atthespreadingstageoftheimpingement.29Atthecontactstage,theinitialimpactontheroughsurfacegeneratesaPWHresultingfromthecompressionofthewaterdropletbehindtheshockwaveenvelope.Thewaterhammerpressurecanbeestimatedas:29

PWHz0.2rCV0

(1)

whereCisthesoundvelocityinwater.Inourwork,thewaterimpactgeneratedaPWHofabout0.32MPaontheroughsurface.Atthespreadingstage,thepressurerapidlyreducestoPDwhilethedropletcontactlineexpands.ThePDcanbeprovidedbytheequation29

PD?0.5rV02

(2)

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estimatedtobeonlyca.0.58kPa.Althoughthewater–airinterfacesbelowthecompressedregionsu?eredapushwithamaximumpressureofca.0.32MPa,theFPSHlmstillkeptitsnon-adhesivesuperhydrophobicproperties.Itsrobustsuper-hydrophobicitycouldbeattributedtoitshighPcapillary([Pwetting)generatedwithinitspetal-likehierarchicalroughstructure.Evenaerimpactingwithaseriesofwaterdroplets(radiusof2.1mm)fromaheightof6cmatadroppingrateofonedropletpersecondformorethan12h,theFPSHlmstillretaineditssuperhydrophobicitywithaWCAofabout153.9???1??(Fig.S11?).SuchasuperhydrophobicFPSHlmcouldalsobeusedunderwaterwherethelmstillpresentedtheanti-wetta-bilitywithstronguorescence(Fig.S12?).

Fig.5(a)TheFPSH?lmcanbepreparedeasilyonthelarge-scaleand?exionalstainlesssteelwovenwiremesh(100mesh).Inset:theWCAmeasurementonaFPSH-enclosingstainlesssteelwovenwiremeshInordertoinvestigatethepossibleapplicationinthedisplaydevices,wealsoevaluatedtheabilitytodisplaypatternsonthisuorescentlmwhenexposedtothe365nmUVlight.AsshowninFig.4d,theletters(top)andtheblade(bottom)cancasttheirshadowsontothelmsataheightofabout4.4mm,leavingtheirspecialshadeswiththeclearboundaries.ThisresultindicatedthattheresultingFPSHlmisauniformuorescentcoating.TheuorescencemicroscopepictureoftheFPSHlmexcitedbythebluelightexhibitedcleanlymanysmallgreenluminousprotuberancesontheuorescentlm(Fig.4e).Whenamicro-gridwiththeborediameterofabout60mmwascoveredontheFPSHlm,theuorescencearraypatternatthemicrometerscalecouldalsobecreated(Fig.4f).