Inward Flow of Intervening Liquid Films Driven by the Marangoni - Zhang et al. - 2021 - Unknown

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pubs.acs.org/LangmuirArticleInwardFlowofInterveningLiquidFilmsDrivenbytheMarangoniEffectduringBubble−SolidCollisionsinEthylAlcohol−NaClAqueousSolutionsXuruiZhang,*RogerioManica,QingxiaLiu,andZhengheXuCiteThis:Langmuir2021,37,4121−4128ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Thedrainagedynamicsofconfinedthinliquidfilmsbetweenanairbubbleandafreshlycleavedmicasurfacewereinvestigatedinethylalcoholaqueoussolutions.Focuswasgiventotheholdingstage,inwhichanunexpectedincreaseinthethicknessofafewhundrednanometersatthecenterofthefilmwascapturedbyinterferometryinethylalcohol−500mMNaClaqueoussolutions.Suchanincreaseinfilmthicknessoccurredwhentheethylalcoholconcentrationexceededthecriticalvalueatabubbleapproachvelocityof100μm/s.Foragivenethylalcoholconcentration,theincreaseinthicknessatthecenterofthefilmdidnothappenwhenthebubbleapproachvelocitywasdecreasedto10μm/s.Comparedtothecasesinethylalcohol−500mMNaClsolutions,noincreaseinthicknessatthecenterofthefilmwasobservedinethylalcohol−watersolutionsunderthesameethylalcoholconcentrationandbubbleapproachvelocity.Thephenomenonoftheincreasingthicknessatthecenterofthefilmwasattributedtothenetinwardflowinthefilm,resultingfromcompetitionbetweentheinwardMarangoniflowandtheoutwarddrainageflowthatwashinderedbythenarrowchannelatthebarrierrimofthefilmunderahighelectrolyteconcentration.TheinwardMarangoniflowwasachievedbyaconcentrationgradientofethylalcoholbetweenthefilmandthebulksolutionresultingfromthemobileair−liquidinterfaceintheinitialapproachingperiod.5,14−16■INTRODUCTIONstudiedbymanyresearchers.AlcoholwasfoundtoinhibitbubblecoalescencetoadifferentdegreedependingontheAlcoholaqueoussolutionsareinvolvedinmanyaspectsofconcentrationandthelengthofhydrocarbontails.Bubblesurfacechemistryandindustrialapplications.Alcoholsarecommonlyusedasco-surfactantsinthepreparationofcoalescenceinalcoholaqueoussolutionshasalsobeenstudied1,2byothermethods,suchasacousticstimulations17andthemicroemulsions.Theinteractionsbetweenbubbles,drops,18andsolidsinalcoholaqueoussolutionsarefundamentalbubblerisingtowardaflatair−liquidinterface.Theeffectofprocessesinmineralflotation,3enhancedoilrecovery,4andalcoholadsorptionattheair−waterinterfaceonbubble5coalescencewasinvestigated.19Studyingthecoalescenceoffermentation.Insuchprocesses,thedrainagedynamicsoftheDownloadedviaKINGABDULLAHUNIVSCITECHLGYonMay14,2021at16:38:44(UTC).interveningliquidfilmsbetweenbubbles,drops,andsolidstwon-hexanedropletsinaqueoussolutionsofn-alcoholsbySeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.dominatetheoutcomeoftheinteraction.Therefore,ahigh-speedcinematographyrevealedanincreaseinthesystematicstudyondrainagedynamicsofthethinliquidfilmscoalescencetimewiththeincreasingalcoholconcentrationininalcoholaqueoussolutionsisaprerequisitetooptimizetheaqueoussolutions.20Allthesestudiesmainlyfocusedontherelevantindustrialprocesses.coalescenceofbubblesordropsinalcoholaqueoussolutionsbyThedrainagedynamicsofthinliquidfilmsinaqueousmeasuringcoalescencetime.Despitetheimportanceofthin6solutionshavebeeninvestigatedextensivelysincethe1930s.liquidfilmsbetweenthebubblesinaqueousalcoholAfterdecadesofresearch,therehasbeenacomprehensivesolutions,21,22thedynamicsofthinliquidfilmdrainagebetweenunderstandingonthedynamicsofthinliquidfilmdrainagethebubblesanddropsthatdeterminethecoalescencehavenotbetweentwobubbles,twodrops,andabubble/dropandasolidbeenreported.surfaceinaqueoussolutionsthroughexperimentaland7−12theoreticalstudies.Theeffectofelectrolytes,surfactants,andotherphysicalparametersondynamicsofthinliquidfilmReceived:December21,2020drainageinaqueoussolutionshasbeenwell-established.Revised:March24,2021However,ourknowledgeofthedynamicsofthinliquidfilmPublished:April2,2021drainageinalcoholaqueoussolutionsisratherlimited,eventhoughresearchonalcoholaqueoussolutionsstarteddecades13ago.Bubblecoalescenceinalcoholaqueoussolutionswas©2021AmericanChemicalSocietyhttps://doi.org/10.1021/acs.langmuir.0c036004121Langmuir2021,37,4121−4128

1Langmuirpubs.acs.org/LangmuirArticleThehydrodynamicboundaryconditionattheair−liquidDeterminationofDrainageDynamicsofThinLiquidFilms.interfaceinanalcoholaqueousmixturethatdeterminestherateThedrainagedynamicsofthinliquidfilmsbetweenanairbubbleof1.2offilmdrainagehasbeenstudiedbyBasarovǎ́etal.23andinourmmradiusandafreshlycleavedmicasurfaceinanethylalcohol24aqueoussolutionwereinvestigatedbyacustom-builtapparatuscalledpreviouswork.Basarovǎ́etal.characterizedthehydrodynamicthedynamicforceapparatus(DFA).ThedetaileddescriptionofDFAboundaryconditionbymeasuringtheterminalrisingvelocityof25couldbefoundinourpreviouspublication.Ineachexperiment,thebubbleswithoutanyinformationoffilmdrainage.Inourairbubblecreatedatoneendofacapillarywasheld300μmabovethepreviouswork,theinitialdrainagestage(whenabubblemicasurfaceandagedfor15mininthesolution.Thedisplacementofapproachedamicasurface)ofthethinliquidfilmbetweenanairthebubblewasdividedintothreestages:approachingperiod,holdingbubbleandamicasurfaceinethylalcohol−NaClaqueousperiod,andretractingperiod.Intheapproachingperiod,theairbubblesolutionswasstudied.Thefilmthicknessofinitialdimplewasmovedtowardthemicasurfaceat10μm/sor100μm/swithatotalformationwasusedtocharacterizethechangeinthedisplacementof400μm.Thebubblethenstayedatthesamepositionhydrodynamicboundaryconditionfromimmobiletomobilefor60sastheholdingperiod,followedbyretractionofthebubblefromthemicasurfacetotheinitialpositionatthesamevelocityasintheattheair−liquidinterfaceastheethylalcoholconcentrationwasapproachingperiod.Thislastperiodwascalledtheretractingperiod.increased.TheinterveningfilmbetweenthebubbleandthemicasurfacedidnotInthisstudy,adifferentdrainagestageofthethinliquidfilmrupturethroughoutthewholeexperiment.Theevolutionofthebetweenanairbubbleandamicasurfaceinethylalcoholobservedinterferencefringesduringtheholdingperiodwasrecordedaqueoussolutionswasinvestigated.Wemainlyfocusontheandanalyzedtoprovidethespatiotemporalfilmthicknessusingcolor26drainagedynamicsofthinliquidfilmsinethylalcohol−NaClinterferometry.Thetimetissettozerowhenthebubblesurfaceisaqueoussolutionswhenthebubblestoppedapproachingandvisiblyflattenedjustbeforethedimpleforms.Thesolutionsinthiswaspressedonthemicasurface.Duringthisstageoffilmstudywereeitherethylalcohol−500mMNaClorethylalcohol−waterdrainage,apronouncedincreaseinthethicknessatthecenterofaqueoussolutionsofthefollowingethylalcoholconcentrations:2.0,3.9,12.1,20.6,43.8,and70.0wt%.Alltheexperimentswerecarriedoutthefilmwasobservedwhentheethylalcoholconcentrationat20°Candperformedintriplicate.exceededathreshold,indicatinganinwardflowofthefilmliquidintheoppositedirectionoffilmdrainage.Thedegreeoftheinwardflowwasfoundtodependontheethylalcohol■RESULTSANDDISCUSSIONconcentrationandbubbleapproachvelocity.TheseresultsThespatiotemporalfilmthicknessbetweenanairbubbleandaprovideamechanismfortheinhibitionofbubblecoalescencefreshlycleavedmicasurfaceinethylalcoholaqueoussolutionsandbubble−solidattachmentinalcoholaqueoussolutionsinduringtheholdingperiodwasdeterminedfromtherecordedmanyengineeringprocesses,suchasfoamgenerationandinterferencefringesbyDFA.Theexperimentalresultsoftheflotation.casesinethylalcohol−500mMNaClaqueoussolutionswithdifferentethylalcoholconcentrationsandbubbleapproach■velocitieswereanalyzedandcomparedwiththecasesinethylEXPERIMENTALSECTIONalcohol−wateraqueoussolutions.Materials.AllaqueoussolutionswerepreparedinMilli-QwaterInwardFlowObservedinEthylAlcohol−500mMNaClwitharesistivityof18.2MΩcmat25°C.AnhydrousethylalcoholwasAqueousSolution.Ingeneral,athinliquidfilmformsbetweenpurchasedfromGreenFieldSpecialtyAlcoholsInc.Sodiumchloride(NaCl)(ACSgrade,FisherScientific)waspurifiedbycalcinationatanairbubbleandasolidsurfaceandtheliquidinthefilmdrains600°Cfor8hbeforeitsuse.MicasurfaceswereacquiredfromTedoutgraduallywhentheairbubbleinteractswiththesolidsurfacePella,Inc.andfreshlycleavedbeforeusetogetacleansurfaceforeachinanaqueoussolution.Thedynamicprocessofthefilmdrainageexperiment.Thecontactanglesofwaterandethylalcoholaqueousinaqueoussolutionshasbeeninvestigatedinmanyprevioussolutionsonthesesurfacesareall0°.studies.27−29Atypicalexampleoftheaxisymmetric“dimple”SurfaceTensionMeasurement.ThesurfacetensionofethylfilmprofileisshowninFigure2a.Theradiusofthefilmisalcoholaqueoussolutions(Figure1)wasmeasuredbythependantdefinedasrrim.Thethicknessatthecenterofthefilm(h(0,t))dropshapemethodusingaThetaOpticalTensiometerT200(Biolincorrespondstothefilmthicknessattheaxisofsymmetry,whileScientific).Todeterminethesurfacetensionofthemeasuredsolution,apendantdropletof12μLwasgeneratedattheendofasyringetipinthethicknessatthebarrierrim(h(rrim,t))correspondstotheair.Then,thedropletshapewascapturedandusedtoobtainthesurfacethinnestfilmthicknessattheborderofthefilm.Theevolutionoftensioninrealtime.Allsolutionsweremeasuredthreetimes.thefilmprofileduringthedrainageprocessin500mMNaClsolutionatanapproachvelocityof100μm/sisshowninFigure2b.Theflatfilmappearedandbecamedimpledintheapproachingperiod.Afterthebubblestoppedmovingandwasheldatsomeposition,thedimplebecamemorepronouncedwhilethefilmthicknesskeptdecreasing.Bothh(0,t)andh(rrim,t)ofthefilmmonotonicallydecreasedintheapproachingandholdingperiods,indicatinganoutwardflowoftheliquidthroughouttheentiredrainageprocess.However,whenethylalcoholwasaddedto500mMNaClsolutionatanethylalcoholconcentrationof20.6wt%,theevolutionofthefilmprofilebecamedrasticallydifferent.AsshowninFigure2c,thethicknessatthecenterandbarrierrimofthefilmdecreasedcontinuouslyintheapproachingperiodupto1.38s.Afterthebubblestoppedmovingat1.4s,h(rrim,t)keptdecreasing,whileh(0,t)graduallyincreasedfrom541nmat4.83sto861nmat21.0s,afterwhichFigure1.Surfacetensionofethylalcohol−500mMNaClandethylthethicknessdecreasedagainwithtime(e.g.,thefilmprofileatalcohol−watersolutionsasafunctionofethylalcoholconcentration.33.4s).Theincreaseinh(0,t)from4.83to21.0sindicatedanet4122https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128

2Langmuirpubs.acs.org/LangmuirArticleFigure2.(a)Schematicillustrationofthethinliquidfilmbetweenanairbubbleandasolidsurfaceinaliquid.Filmprofileevolutionofanairbubbleof1.2mmradiusmovingtowardafreshlycleavedmicasurfaceatanapproachvelocityof100μm/sin(b)500mMNaClsolutionand(c)ethylalcohol−500mMNaClaqueoussolutionwithanethylalcoholconcentrationof20.6wt%.Opensymbolsrepresentthefilmprofilesduringtheapproachingperiod,whilesolidsymbolsindicatethefilmprofilesintheholdingperiod.Figure3.Filmprofileevolutionintheholdingperiodofanairbubbleof1.2mmradiusmovingtowardafreshlycleavedmicasurfaceatanapproachvelocityof100μm/sinethylalcohol−500mMNaClaqueoussolutionswithdifferentethylalcoholconcentrations:(a)2.0wt%,(b)3.9wt%,(c)12.1wt%,(d)43.8wt%,(e)70.0wt%,and(f)100wt%.ThereproducibilityoftheexperimentisshowninFigureS1intheSupportingInformation.inwardflowoftheliquid,whichpushedtheair−liquidinterfacesurfaceinethylalcohol−500mMNaClaqueoussolutions,upwardatthecenterofthefilm.Suchliquidflowwasoppositetoespeciallytheroleofethylalcoholontheinwardflowbehavior.thetypicalflowdirectionoffilmdrainage.AsimilarincreaseofEffectofEthylAlcoholConcentration.Asmentionedh(0,t)betweenamercurydropletandaflatsolidsurfaceinanabove,theadditionofethylalcoholtothe500mMNaClaqueoussolutionwasreportedbyConnoretal.30Theysolutionresultedintheincreaseofh(0,t)intheholdingperiodoffilmdrainage.Therefore,theinfluenceofethylalcoholattributedsuchbehaviortothedifferenceinthemercury/concentrationonthisinwardflowisessentialanddiscussedinelectrolyteinterfacialtensionasafunctionofappliedpotential.thissection.Comparedwiththelittleincreaseofh(0,t)(about10nm)inThetimeevolutionoffilmprofilesintheholdingperiodtheirexperiments,theincreaseofh(0,t)inourcasewasmorebetweenthebubbleandthemicasurfaceatanapproachvelocitypronounced(320nm)intheholdingperiod.Suchabigincreaseof100μm/sindifferentethylalcohol−500mMNaClaqueousofh(0,t)hasnotbeenreportedbeforeandinspiresustosolutionsisshowninFigure3.ThedifferenceinthedimpleinvestigatethemechanismofthisinwardflowduringthefilmheightinFigure3wasduetothechangeintheboundarydrainageintheholdingperiodofthebubblepressedonthemicaconditionattheair−liquidinterfacewiththeincreasingethyl4123https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128

3Langmuirpubs.acs.org/LangmuirArticle24alcoholconcentration,asdiscussedinourpreviouswork.theholdingperiod.ForthecasesofethylalcoholconcentrationWhentheethylalcoholconcentrationwaslessthan3.9wt%,noof20.6,43.8,and70.0wt%,theplateaulastedonlyforaround8increaseofh(0,t)wasobservedintheholdingperiod(Figures,followedbyagradualdecreaseinh(0,t).Sincetheinwardflow3a,b).Oncetheethylalcoholconcentrationwasincreasedtooccurredatanearliertimeintheholdingperiodforthecaseofa12.1wt%,h(0,t)startedtoincreaseby167nmintheholdinghigherethylalcoholconcentration,h(0,t)startedtodecreaseperiod(Figure3c).Theh(0,t)increasedby320,203,and140earlieraftertheplateauathigherethylalcoholconcentrations.nmintheholdingperiodwiththefurtherincreaseintheethylToquantifytheinwardflowoftheliquidtowardthecenterofalcoholconcentrationto20.6,43.8,and70.0wt%(Figures2cthefilm,thevolumeoftheliquidinsidethefilmforeachfilmand3d,e),respectively.However,nonoticeableincreaseofh(0,profile(i.e.,thevolumeoftheliquidbyrevolvingtheshadedareat)wasobservedin100wt%ethylalcohol,asshowninFigure3f.aroundthezaxisinFigure2a)wasobtainedbytheintegrationofTheseresultsindicatethattheincreaseinh(0,t)onlyoccurredthefilmusingthefollowingequationinthemixtureofethylalcoholand500mMNaClsolutionatanrrimethylalcoholconcentrationhigherthanthethresholdvalueofVt()=∫2πrhrtr(,)d12.1wt%.0(1)Tounderstandtheinwardflowfeature,h(0,t)wasplottedasawhereristheradialcoordinate,rrimisthefilmradius,andh(r,t)functionoftime,asshowninFigure4a,b.Itclearlyshowsthatisthespatiotemporalfilmthickness.Theexcessvolumeoftheliquid(V(t)excess)inthefilm(definedasthedifferenceintheliquidvolumeofthefilmatthebeginningoftheplateauandthatwhentheincreaseinh(0,t)firstappeared,thatis,V(t)excess=V(21.0s)−V(4.83s)wasthencalculated.AsshowninFigure4c,theexcessvolumeoftheliquidinthefilmisintheorderofpicoliters,whichisnotsurprisingforsuchathinliquidfilm(thefilmthicknessis3ordersofmagnitudesmallerthanthefilmradius).ThepositivevalueofV(t)excessindicatesanetflowofliquidintothefilmdespitetheoutwardflowatthebarrierrim.ThenegativevalueofV(t)excessindicatesanetflowofliquiddrainingoutofthefilmeventhoughtherewasaninwardflowatthecenterofthefilm.Thus,alargerpositivevalueofV(t)excessrepresentsastrongerinwardflowinthefilm.AsshowninFigure4c,theinwardflowbecameprogressivelystrongerwiththeincreasingethylalcoholconcentration,peakedwhentheethylalcoholconcentrationreached20.6wt%,andthenweakenedastheethylalcoholconcentrationfurtherincreased.Theseresultsconfirmthatthemostpronouncedinwardflowoccurredattheethylalcoholconcentrationof20.6wt%.EffectofApproachVelocity.Theexperimentalresultsmentionedaboveforthedynamicdrainageofthinliquidfilmsbetweentheairbubbleandthemicasurfaceinethylalcohol−500mMNaClaqueoussolutionswereobtainedattheapproachvelocityof100μm/s.Here,theimpactofapproachvelocityontheinwardflowbehaviorwasstudied.Thetimeevolutionofh(0,t)forthecasesofbubbleapproachvelocityat10μm/sinethylalcohol−500mMNaClaqueoussolutionswithethylalcoholconcentrationsof12.1,20.6,43.8,and70.0wt%isshowninFigure5(thecorrespondingevolutionoffilmprofilesisgivenintheSupportingInformationasFigureS2).Comparedwiththeresultsofthebubbleapproachvelocityof100μm/s,therewasnoincreaseinh(0,t)whenthebubbleFigure4.(a,b)Thicknessatthecenterofthefilmasafunctionoftimeapproachvelocitydecreasedto10μm/sforcaseswith12.1,20.6,foranairbubbleinteractingwithafreshlycleavedmicasurfaceinethyland43.8wt%ethylalcoholconcentrations.Onlywhentheethylalcohol−500mMNaClaqueoussolutionswithdifferentethylalcoholalcoholconcentrationwasincreasedto70.0wt%,h(0,t)concentrations.Theapproachvelocityoftheairbubblewas100μm/s.increasedby10nmincomparisonwithhundredsofnanometersTheverticaldashedlinemarkstheboundarybetweentheapproachingperiodandtheholdingperiod.(c)ExcessvolumeoftheliquidforthecasesinFigure3.(V(t)excess)inthefilmcorrespondingtothecasesin(b).EffectofElectrolyteConcentration.Inordertounder-standtheroleofelectrolyteconcentrationontheinwardflowbehavior,similarexperimentswereconductedinethylalcohol−therewasnoincreaseofh(0,t)whentheethylalcoholwatersolutionswithdifferentethylalcoholconcentrationsandconcentrationwaslessthan3.9and100wt%(Figure4a).Theatdifferentbubbleapproachvelocities.Theresultsoftimeincreaseinh(0,t)occurredatanearliertimewiththeincreasingevolutionofh(0,t)areplottedinFigure5(thecorrespondingethylalcoholconcentration(Figure4b).AfterreachingtheevolutionoffilmprofilescouldbefoundintheSupportinglargestvalueofh(0,t)ineachcase,aplateauwasformedratherInformationinFiguresS3andS4).Inspiteoftheethylalcoholthananimmediatedecreaseinh(0,t).Forthecaseof12.1wt%concentrationandapproachvelocity,thepronouncedinwardethylalcoholconcentration,theplateaulasteduntiltheendofflowwasnotobservedforallthecaseswithoutNaCl.Onlywhen4124https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128

4Langmuirpubs.acs.org/LangmuirArticleFigure5.Thicknessatthecenterofthefilmasafunctionoftimewhenanairbubbleapproachedafreshlycleavedmicasurfaceatdifferentbubbleapproachvelocitiesinethylalcoholaqueoussolutionswithdifferentelectrolyteconcentrationsandethylalcoholconcentrationsof(a)12.1wt%,(b)20.6wt%,(c)43.8wt%,and(d)70.0wt%.40theethylalcoholconcentrationwasincreasedto43.8and70.0interfaceforionsisreducedbyethylalcoholandNaClisa41wt%atbubbleapproachvelocityof100μm/s,therewasasmallsurface-excludedelectrolyte.Therefore,theconcentrationofincreaseinh(0,t)(20and80nm).Theseresultsconfirmedthatethylalcoholattheair−aqueoussolutioninterfaceisstillbesidestheadditionofethylalcoholinaqueoussolutions,thesignificantlyhigherthanthatinthebulkeventhroughthepresenceofanelectrolyteisalsothekeytotheformationofelectrolyteispresentinthesolution.Ithasbeenshowninour24pronouncedinwardflowinethylalcoholaqueoussolution.previousworkthattheair−liquidinterfacewaspartiallyorInwardMarangoniFlow.Accordingtothelitera-fullymobilewithabubbleapproachvelocityof100μm/swhen10,31,32ture,theMarangonieffectisthegeneralcauseofthetheethylalcoholconcentrationwas12.1,20.6,43.8,and70.0wtreversedflowinthedrainageprocessofthinliquidfilmsthat%intheinitialdrainageprocess.Intheinitialapproachingslowsdowntheoutwarddrainage.Thus,itispossiblethattheperiod,boththeaqueoussolutionandethylalcoholquicklyflewMarangonieffectcouldbestrongenoughtoovercometheoutwardfromthefilmthroughtheinterfacialregion.Ahigheroutwardflowtocreateanetinwardflowinsomeconditions,concentrationofethylalcoholattheair−liquidinterfaceledtowhichhasbeenreportedtoleadtoaphysicalreboundbetweenanadditionalamountofethylalcoholtodrainoutofthefilm,33twodropsatahighcollidingvelocity.Basedontheresultinginalowerethylalcoholconcentrationinthefilmexperimentalresultsmentionedabove,itisreasonabletocomparedtothatinthebulksolution.Asaresult,theinterfacialspeculatethatthepronouncedinwardflowinthisstudywastensionoftheair−liquidinterfacebecamehigherinthefilmthancausedbyMarangoniflowinducedbyasurfacetensiongradientthatinthebulksolution(Figure1),givingrisetoaninwardalongtheair−liquidinterfaceinethylalcohol−NaClaqueousMarangoniflowintheholdingperiod.Theincreaseofh(0,t)solutions.Inthissection,wewilldiscusstheoriginofthesurfaceshowninFigures2c,3c−ecanbeattributedtothedominanttensiongradientformedattheair−liquidinterfaceintheholdinginwardMarangoniflowcomparedtotheoutwarddrainageflow.periodduringthedrainageofthefilmbetweentheairbubbleAtthevelocityof100μm/s,theshearstressoftheoutward29andthesolidsurfaceinethylalcohol−NaClaqueoussolutions.drainageflowwasfoundtobelessthan1Pa.TheinterfacialAsthesystemwassealedandthebubbleonlycontainedatensiongradientof0.1mN/malongthearound100μmsmallvolumeofairinthisstudy,ethylalcoholinthebubbleandtransitionregionwouldbesufficienttogenerateMarangonithesolutionshouldreachequilibriumafteragingtimebeforestressof1Patoovercometheshearstressofoutwarddrainageeachexperiment.Thus,thesurfacetensiongradientcouldnotbeflow.Theearlierformationoftheinwardflowatahighethylcausedbytheevaporationofethylalcoholintothebubblethatalcoholconcentrationmightbeduetothehighdegreeofresultsinthe“tearsofwine”intheopensystem.Itiswell-knownmobilityoftheair−liquidinterfaceastheethylalcoholthatethylalcoholconsistsofahydrophilicheadwithashortconcentrationwasincreased.Theair−liquidinterfacewasnon-polarhydrocarbontail,whichconfersaweakamphiphilicimmobileinthecasesoflowethylalcoholconcentration(2.9property.Asaresult,intheethylalcohol−watersolution,ethyland3.9wt%)sothatitcouldnotgenerateinwardMarangonialcoholtendstoenrichattheair/waterinterface,leadingtoflow.Forthecaseof100%ethylalcohol,theair−liquidinterfacehigherconcentrationofethylalcoholatthesurfacelayerwasmobile,butitcouldnotcreateaconcentrationgradient.Atcomparedtothatinthebulk.Thisfacthasbeenstudiedthelowbubbleapproachvelocityof10μm/s,theair−liquid34,35experimentallybymassspectrometry,sum-frequencyinterfacewasimmobilewhentheethylalcoholconcentration36,37generationvibrationalspectroscopy,andneutronreflec-was12.1wt%sothattheinwardMarangoniflowcouldnotbe38,3939tionandtheoreticallybymoleculardynamicssimulationcreated.Astheethylalcoholconcentrationwasincreasedtoandhasbeenwell-acceptedsincetheearly20thcentury.Inethyl20.6,43.8,and70wt%,eventhoughtheair−liquidinterfacealcohol−NaClaqueoussolution,theavailablespacewithinthebecamemobile,resultinginanethylalcoholconcentration4125https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128

5Langmuirpubs.acs.org/LangmuirArticlegradientintheinitialapproachingperiod,theinwardMarangonialcohol−NaClaqueoussolution(FigureS5),themostflowcouldnotbegeneratedtoincreaseh(0,t)intheholdingpronouncedinwardflowonlyoccurredwhentheethylalcoholperiod.Bycomparingtheapproachingperiodof4.5sattheconcentrationwas20.6wt%.velocityof100μm/s,theapproachingperiodof45satthevelocityof10μm/swaslongenoughtoallowethylalcoholto■CONCLUSIONSdiffusebackfromthehighconcentrationofthebulksolutiontoWereportedanovelphenomenonofinwardflowdrivenbythethelowconcentrationofthefilm.Asaresult,theethylalcoholMarangonieffectduringthefilmdrainagebetweenabubbleandconcentrationinthefilmandthebulksolutionwasequalizedatafreshlycleavedmicasurfaceinethylalcohol−NaClaqueousthebeginningoftheholdingperiod.solutions.ThenetinwardflowoccurredifthefollowingTounderstandhowtheelectrolyteinfluencedtheinwardconditionsweremet:(1)theair−liquidinterfaceshouldbeMarangoniflow,theexperimentaldataofh(0,t)andh(rrim,t)inpartiallyorfullymobileintheinitialapproachingperiodtothecaseof20.6wt%ethylalcoholconcentrationinethylcreateinwardMarangoniflowinthefilm;(2)theinwardalcohol−500mMNaClwerecomparedwiththatinethylMarangoniflowneedstobesufficientlystrongtoovercomethealcohol−watersolution(Figure6).Asshownintheinsetofoutwardflow,whichreliesonthebubbleapproachvelocityandethylalcoholconcentrationintheethylalcoholaqueoussolution;and(3)theoutwarddrainageflowissoweakthatitcouldbeeasilyovercomebytheinwardMarangoniflow,whichreliesonthenarrowchannelatthebarrierrimofthefilm.Ourfindingsareapplicabletothebubblecoalescenceandbubble−solidattachmentinalcoholaqueoussolutionsastheinwardflowinhibitsthefilmthinningtobecomeahindrancetotheaboveprocesses.Incombinationwithourpreviousstudyofthehydrodynamicboundaryconditionattheair−liquidinterfacein24ethylalcoholaqueoussolutions,thisstudyprovidesacomprehensiveunderstandingofthewholedrainagedynamicsofthinliquidfilmsinvolvingbubblesinethylalcoholaqueoussolutions.FurthereffortstodevelopanappropriatetheoreticalmodeltoquantifytheinwardMarangoniflowareunderwaysothattheinwardflowbehaviorcouldbequantitativelyexplained,Figure6.Comparisonofthetimeevolutionofh(0,t)andh(rrim,t)andthepredictioncouldbemadebasedontheinformationfromwhenanairbubblewasdriventowardafreshlycleavedmicasurfaceat100μm/sinethylalcohol−500mMNaClandethylalcohol−waterthemodel.solutionsof20.6wt%ethylalcoholconcentration.Theverticaldashedlinemarkstheboundarybetweentheapproachingperiodandthe■ASSOCIATEDCONTENTholdingperiod.Theinsetshowstheevolutionofh(0,t)andh(rrim,t)in*sıSupportingInformationtheapproachingperiod.TheSupportingInformationisavailablefreeofchargeathttps://pubs.acs.org/doi/10.1021/acs.langmuir.0c03600.Figure6,thedrainagerateofthethinliquidfilmwasthesameinReproducibilityoftheexperiment;timeevolutionoffilmethylalcohol−NaClandethylalcohol−watersolutionsintheprofilesatanapproachvelocityof10μm/sinethylinitialapproachingperiod,indicatingsimilarinwardMarangonialcohol−500mMNaClaqueoussolutionsand100μm/sflowinthesetwosolutions.However,atthebeginningoftheand10μm/sinethylalcohol−watersolutions;timeholdingperiod,astherepulsiveelectrostaticdoublelayerforceevolutionofh(rrim,t)atavelocityof100μm/sinethylcanessentiallybenegligiblein500mMNaClsolution,thealcohol−500mMNaClaqueoussolutions(PDF)barrierrimofthefilminethylalcohol−NaClaqueoussolutionquicklydrainedtoreachathinnerfilmthickness(about30nm).VideoofinterferenceringsofthethinliquidfilmbetweenSuchathinfilmgeneratedaverynarrowchannelatthebarrierthebubbleandthesolidsurfaceatavelocityof100μm/srimfortheliquidinsidethefilmtodrainout,whichrestrictedtheinethylalcohol−500mMNaClaqueoussolutionswithandrainageoftheliquidatthecenterofthefilm.Thisslowdrainageethylalcoholconcentrationof20.6wt%(AVI)rateatthecenterofthefilmcausedbyhighelectrolyte29concentrationhasalsobeenshowninourpreviouswork.Asaconsequence,theinwardMarangoniflowcouldovercomethe■AUTHORINFORMATIONoutwarddrainageflowtoincreaseh(0,t)intheholdingperiod.CorrespondingAuthorOntheotherhand,duetothedominantrepulsiveelectrostaticXuruiZhang−StateKeyLaboratoryforStrengthandVibrationdoublelayerforceinwater,thethicknessofthebarrierrimoftheofMechanicalStructures,SchoolofAerospaceEngineering,filmwasquitethicker(about160nm)inethylalcohol−waterXi’anJiaotongUniversity,Xi’an710049,China;DepartmentsolutionatthebeginningoftheholdingperiodcomparedtothatofChemicalandMaterialsEngineering,UniversityofAlberta,inethylalcohol−NaClaqueoussolution.TheliquidinsidetheEdmonton,AlbertaT6G1H9,Canada;orcid.org/0000-filmcouldeasilyflowout,resultinginthefastdrainageofthefilm0003-0801-5760;Email:xurui_zhang@xjtu.edu.cnatthecenter,asshowninFigure6,thatwasnotabletoovercomebytheinwardMarangoniflow.ThisisthereasonwhythereisnoAuthorsincreaseofh(0,t)intheholdingperiodinethylalcohol−waterRogerioManica−DepartmentofChemicalandMaterialssolutions.Similarly,becauseh(rrim,t)becamethickerwhentheEngineering,UniversityofAlberta,Edmonton,AlbertaT6Gethylalcoholconcentrationexceeded20.6wt%inethyl1H9,Canada;orcid.org/0000-0002-2247-45364126https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128

6Langmuirpubs.acs.org/LangmuirArticleQingxiaLiu−DepartmentofChemicalandMaterials(15)Keitel,G.;Onken,U.InhibitionofBubbleCoalescencebyEngineering,UniversityofAlberta,Edmonton,AlbertaT6GSolutesinAir/WaterDispersions.Chem.Eng.Sci.1982,37,1635−1H9,Canada1638.ZhengheXu−DepartmentofChemicalandMaterials(16)Drogaris,G.;Weiland,P.CoalescenceBehaviourofGasBubblesinAqueousSolutionsofn-AlcoholsandFattyAcids.Chem.Eng.Sci.Engineering,UniversityofAlberta,Edmonton,AlbertaT6G1983,38,1501−1506.1H9,Canada;DepartmentofMaterialsScienceand(17)Kracht,W.;Finch,J.A.UsingSoundtoStudyBubbleEngineering,SouthernUniversityofScienceandTechnology,Coalescence.J.ColloidInterfaceSci.2009,332,237−245.Shenzhen518055,China(18)Ghosh,P.CoalescenceofAirBubblesatAir−WaterInterface.Completecontactinformationisavailableat:Chem.Eng.Res.Des.2004,82,849−854.https://pubs.acs.org/10.1021/acs.langmuir.0c03600(19)Srinivas,A.;Ghosh,P.CoalescenceofBubblesinAqueousAlcoholSolutions.Ind.Eng.Chem.Res.2012,51,795−806.(20)Sagert,N.H.;Quinn,M.J.TheCoalescenceofN-HexaneNotesDropletsinAqueousSolutionsofn-Alcohols.Can.J.Chem.Eng.1979,Theauthorsdeclarenocompetingfinancialinterest.57,29−34.(21)Qu,X.;Wang,L.;Karakashev,S.I.;Nguyen,A.V.Anomalous■ThicknessVariationoftheFoamFilmsStabilizedbyWeakNon-IonicACKNOWLEDGMENTSSurfactants.J.ColloidInterfaceSci.2009,337,538−547.Wegratefullyacknowledgethefinancialsupportfromthe(22)Wang,L.;Yoon,R.-H.EffectsofSurfaceForcesandFilmFundamentalResearchFundsfortheCentralUniversities(no.ElasticityonFoamStability.Int.J.Miner.Process.2008,85,101−110.xxj022020012)andtheChinaPostdoctoralScienceFoundation(23)Basarová,P.;Pišlová,J.;Mills,J.;Orvalho,S.Influenceof̌(grantno.2019M663675).ThisworkwasalsopartiallyMolecularStructureofAlcohol-WaterMixturesonBubbleBehavioursupportedbytheNaturalSciencesandEngineeringResearchandBubbleSurfaceMobility.Chem.Eng.Sci.2018,192,74−84.(24)Zhang,X.;Manica,R.;Tang,Y.;Liu,Q.;Xu,Z.BubbleswithCouncil(NSERC)IndustrialResearchChairPrograminOilTunableMobilityofSurfacesinEthanol-NaClAqueousSolutions.J.SandsEngineeringandAlbertaInnovates-EnergyandEnviron-ColloidInterfaceSci.2019,556,345−351.mentalSolutions(AI-EES),Canada.(25)Zhang,X.;Tchoukov,P.;Manica,R.;Wang,L.;Liu,Q.;Xu,Z.SimultaneousMeasurementofDynamicForceandSpatialThinFilm■ThicknessbetweenDeformableandSolidSurfacesbyIntegratedThinREFERENCESLiquidFilmForceApparatus.SoftMatter2016,12,9105−9114.(1)Kumar,P.;Mittal,K.L.HandbookofMicroemulsionScienceand(26)Butler,C.S.;Seeger,Z.L.E.;Bell,T.D.M.;Bishop,A.I.;Tabor,Technology;CRCpress,1999;pp139−184.R.F.LocalDeterminationofThinLiquidFilmProfilesUsingColour(2)Zana,R.AqueousSurfactant-AlcoholSystems:AReview.Adv.Interferometry.Eur.Phys.J.E2016,39,14.ColloidInterfaceSci.1995,57,1−64.(27)Hewitt,D.;Fornasiero,D.;Ralston,J.;Fisher,L.R.AqueousFilm(3)Elmahdy,A.M.;Mirnezami,M.;Finch,J.A.ZetaPotentialofAirDrainageattheQuartz/Water/AirInterface.J.Chem.Soc.,FaradayBubblesinPresenceofFrothers.Int.J.Miner.Process.2008,89,40−43.Trans.1993,89,817−822.(4)Dahami,M.A.;Constant,W.D.;Wolcott,J.M.Alcohol-Assisted(28)Manica,R.;Chan,D.Y.C.DrainageoftheAir−Water−QuartzAlkalineFloodingforEnhancedOilRecovery.Fuel1988,67,1242−Film:ExperimentsandTheory.Phys.Chem.Chem.Phys.2011,13,1248.1434−1439.(5)Oolman,T.O.;Blanch,H.W.BubbleCoalescenceinStagnant(29)Zhang,X.;Manica,R.;Tchoukov,P.;Liu,Q.;Xu,Z.EffectofLiquids.Chem.Eng.Commun.1986,43,237−261.ApproachVelocityonThinLiquidFilmDrainagebetweenanAir(6)Derjaguin,B.;Kussakov,M.AnomalousPropertiesofThinBubbleandaFlatSolidSurface.J.Phys.Chem.C2017,121,5573−PolymolecularFilms.ActaPhysicochim.URSS1939,10,25−44.5584.(7)Chan,D.Y.C.;Klaseboer,E.;Manica,R.FilmDrainageand(30)Connor,J.N.;Horn,R.G.TheInfluenceofSurfaceForcesonCoalescencebetweenDeformableDropsandBubbles.SoftMatterThinFilmDrainagebetweenaFluidDropandaFlatSolid.Faraday2011,7,2235−2264.Discuss.2003,123,193−206.(8)Liu,B.;Manica,R.;Xu,Z.;Liu,Q.TheBoundaryConditionatthe(31)Karakashev,S.I.;Tsekov,R.Electro-MarangoniEffectinThinAir-LiquidInterfaceandItsEffectonFilmDrainagebetweenCollidingLiquidFilms.Langmuir2011,27,2265−2270.Bubbles.Curr.Opin.ColloidInterfaceSci.2020,50,101374.(32)Tsekov,R.;Ivanova,D.S.;Slavchov,R.;Radoev,B.;Manev,E.(9)Horn,R.G.;Asadullah,M.;Connor,J.N.ThinFilmDrainage:D.;Nguyen,A.V.;Karakashev,S.I.StreamingPotentialEffectontheHydrodynamicandDisjoiningPressuresDeterminedfromExper-DrainageofThinLiquidFilmsStabilizedbyIonicSurfactants.imentalMeasurementsoftheShapeofaFluidDropApproachingaLangmuir2010,26,4703−4708.SolidWall.Langmuir2006,22,2610−2619.(33)Chevaillier,J.-P.;Klaseboer,E.;Masbernat,O.;Gourdon,C.(10)Carnie,S.L.;DelCastillo,L.;Horn,R.G.MobileSurfaceChargeEffectofMassTransferontheFilmDrainagebetweenCollidingDrops.CanImmobilizetheAir/WaterInterface.Langmuir2019,35,16043−J.ColloidInterfaceSci.2006,299,472−485.16052.(34)Raina,G.;Kulkarni,G.U.;Rao,C.N.R.SurfaceEnrichmentin(11)Webber,G.B.;Manica,R.;Edwards,S.A.;Carnie,S.L.;Stevens,Alcohol−WaterMixtures.J.Phys.Chem.A2001,105,10204−10207.G.W.;Grieser,F.;Dagastine,R.R.;Chan,D.Y.C.DynamicForces(35)Raina,G.;Kul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7Langmuirpubs.acs.org/LangmuirArticle(39)Li,Z.X.;Lu,J.R.;Styrkas,D.A.;Thomas,R.K.;Rennie,A.R.;Penfold,J.TheStructureoftheSurfaceofEthanol/WaterMixtures.Mol.Phys.1993,80,925−939.(40)Gao,G.;Nguyen,C.V.;Phan,C.M.MolecularArrangementbetweenElectrolyteandAlcoholattheAir/WaterInterface.J.Mol.Liq.2017,242,859−867.(41)Levin,Y.;DosSantos,A.P.;Diehl,A.IonsattheAir-WaterInterface:AnEndtoaHundred-Year-OldMystery?Phys.Rev.Lett.2009,103,257802.4128https://doi.org/10.1021/acs.langmuir.0c03600Langmuir2021,37,4121−4128