E ff ect of Sodium Dodecyl Sulfonate on the Foam Stability and Adsorption Con fi guration of Dodecylamine at the Gas − Liquid Interface

《E ff ect of Sodium Dodecyl Sulfonate on the Foam Stability and Adsorption Con fi guration of Dodecylamine at the Gas − Liquid Interface》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

pubs.acs.org/LangmuirArticleEffectofSodiumDodecylSulfonateontheFoamStabilityandAdsorptionConfigurationofDodecylamineattheGas−LiquidInterfaceXimeiLuo,QiqiangLin,ShumingWen,YunfanWang,*HaoLai,LinpingQi,XuetongWu,YongfengZhou,andZhenguoSongCiteThis:Langmuir2021,37,1235−1246ReadOnlineACCESSMetrics&MoreArticleRecommendationsABSTRACT:Inthisstudy,theeffectofsodiumdodecylsulfonate(SDS)onthefoamstabilityofdodecylamine(DDA)andonitsadsorptionconfigurationatthegas−liquidinterfacewasinvestigated.Frothstabilityexperiments,surfacetensionmeasurements,time-of-flightsecondary-ionmassspectrometrymeasurements,andmoleculardynamicssimulationcalculationswereperformedinthisinvestigation.TheresultsrevealedthatthefoamstabilityofDDAsolutionwasextremelystrong,andtheadditionofSDScoulddecreasethefoamstabilitywhentheconcentrationofDDAwaslessthanacertainvalue.Thedecreaseinfoamstabilitycouldbeascribedtoseveralreasons,namely,thebigcross-sectionalareaofSDSatthegas−liquidinterfaceandlowadsorptioncapacityofsurfactantsatthegas−liquidinterface,thehighsurfacetension,thechangeinthedouble-layerstructure,thesmallthicknessofthegas−liquidinterfaciallayer,theweakinteractionintensitybetweentheheadgroupsofthesurfactantsandthewatermolecules,thestrongmovementabilityofthewatermoleculesaroundtheheadgroups,andthesparseandlessuprightarrangementconfigurationofmoleculesatthegas−liquidinterface.ThesefindingscangreatlyhelpinsolvingthestrongfoamstabilityprobleminDDAflotationandprovideamethodforreducingfoamstability.18−24■INTRODUCTIONsurfactantactivityandleadtoanobvioussynergisticeffect.Foralongtime,scholarsbelievedthatanionicandcationicFoamisakindofdispersionsystemwithnumerousbubblesdispersedintheliquidcontinuousphase.Thissystemisasurfactantscannotbecombinedbecauseoftheriskofthermodynamicallyunstablesystemwithatendencytodecreaseprecipitationorinstability.However,recentstudiesconfirmedtheboundareaandsurfaceenergyspontaneously.1Foamisthatmixedsurfactantspossessnumerousexcellentproperties,extensivelyusedinseveralfields,suchasthedailychemicalincludingeffectivedecontamination,solubilization,satisfactoryDownloadedviaUNIVOFCALIFORNIASANTABARBARAonMay16,2021at10:42:44(UTC).Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.25−28industry,food,mineralflotation,metallurgy,firefighting,andoilfoamperformance,andefficientdisinfection.Mixedmining.Foamstabilityisanimportantconceptinfoamresearchsurfactantsarenowbroadlyusedbecauseoftheirstrong29−34andakeyfactorinfoamapplications.Foamhasvarioussynergisticeffect.First,thestrongelectrostaticinteractionadvantagesanddisadvantages.Thebenefitsofusingfoamarebetweenanionicandcationicsurfactantsgreatlyreducestheprominentinthefieldsofmineralprocessing,soapindustries,absorptionfreeenergyofeachcomponentinthemixedsystem,andfirefighting,whereasitsharmfuleffectsarenoticeableintherebyimprovingthesurfaceactivity.Second,theionscanbesolutionconcentrationandvacuumdistillationprocesses.replacedwithsurfaceactiveionswithoppositechargestoreduceTherefore,foamstabilityshouldberegulatedandthestabilitytheelectrostaticrepulsion,andthehydrocarbonchainarrange-mechanismshouldbeanalyzed.mentiscompact.Last,thehydrophobicgroupsofthecationicDodecylamine(DDA)isusedasacationiccollectorfor2−4silicates,oxidizedminerals,andcarbonateminerals.Cationicflotationhasseveraladvantages,includingasimplereagentReceived:November10,2020regime,lowcost,andlowtemperaturerequirement.2,5−12Revised:January4,2021However,theextremelyhighfoamstabilityisamajorproblemPublished:January12,202113−17associatedwithDDAapplicationsinflotation.Therefore,theissueoffoamstickinessofDDAhasreceivedconsiderableattention.Mixedanionic−cationicsurfactantscanimprovethe©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c032481235Langmuir2021,37,1235−1246

1Langmuirpubs.acs.org/LangmuirArticle63,64andanionicsurfactantscanactwitheachotherandthusgreatlyobtainexperimentally.IthasbeenproventhattheSandwich65−68enhancetheassociationbetweenthetwosurfactants.Asaresult,modelisfeasibletostudythegas−liquidinterface.themixedsurfactantscaneasilyadsorbattheinterfaceandHowever,thesimulationcalculationresultsshouldbecombinedsurface,formmicellesinthesolution,andshowahighsurfacewithotherexperimentaldataordetectionmethodsbecauseactivity.Nonetheless,thecationicsurfactantsmixedwithsimulationcalculationalonecannotfullysimulatearealsolutionanionicsurfactantsarerarelyusedtoregulatethefoamstability,environment.Time-of-flightsecondary-ionmassspectrometryandtheunderlyingmechanismisnotthoroughlyexplored.The(ToF-SIMS)isasurfaceanalysistechniquewithextremelyhighcommonmethodsforadjustingfoamstabilityincludephysicalresolution.Itcancollectandanalyzethesecondaryions35,36andchemicalapproaches.Examplesofphysicalmethodsareremovingfromthesurfaceafterbombardmentbyprimary-ion69fluidinjection,static,ultrasonic,heatingorpressure,mechanicalbeams.Additionally,itcanobtaintheinformationofagitation,anddecompression(vacuumextraction)methods.individualelementsandmolecularspeciesaswellashaveanFluidinjectionisthecommonlyusedphysicalmethodforinsightintobindingphenomena,molecularorientation,and70,71defoaminginflotation.However,thistechnologyisinsufficient,configurationinformation.Thus,ToF-SIMScanprovideaisinefficient,wastesalargeamountofwaterresources,andnewwaytoinvestigatethemicro-configurationofthegas−liquiddilutesthepulp.Thechemicalapproachesincludechemicalinterface.Moreover,thecombinedapplicationofthetworeactionanddefoameradditionmethods.Thechemicalreactionmethods(MDsimulationandToF-SIMS)isveryrare.methodproducesinsolublesubstances,whichareharmfultotheInthispaper,theeffectofsodiumdodecylsulfonate(SDS)onequipment.AlthoughdefoameradditionisaconvenientthefoamstabilityofDDAandonitsadsorptionconfigurationatapproach,thismethodhasalowdefoamingefficiencyandthegas−liquidinterfacewasinvestigated.Frothstabilityhighconditionrequirement.Inaddition,thistechniquemainlyexperiments,surfacetensionmeasurements,ToF-SIMSmeas-involvesthefoamproductafterflotation,anditcannotsolvetheurements,andMDsimulationswereperformedinthisproblemscausedbyfoamstickinessduringflotation(e.g.,investigation.ThisstudycombinesToF-SIMSmeasurementsentrainment).Comparedwithotherapproaches,themethodofandMDsimulationcalculationstoobtainthestructuraladjustingthefoamstabilitybyusingamixedcationic−anionicinformationattheatomiclevelandthemicro-configurationofsurfactantnotonlydirectlyadjuststhefoamstabilityduringthesurfactantsatthegas−liquidinterfacetheoreticallyandflotationbutalsoimprovestheflotationefficiencyandproductexperimentally.TheresultspresentusefulknowledgeonhowtoqualityduetothesynergisticeffectofthecombinationofsolvetheproblemofstrongfoamstabilityinDDAflotation,cationicandanioniccollectors.Theresultsofourpresentstudyprovideatheoreticalbasistoguidethedesignofamineindicatethatinthereverseflotationofhematitebyusingcationicsurfactants,andintroduceamethodfordecreasingfoamandanionicsurfactants,theflotationindexishigh,andthestability.inhibitordosageislow.Therefore,investigatingthepropertiesofmixedcationicandanionicsurfactantsisessentialtoregulate■MATERIALSANDMETHODSfoamstability.Reagents.Analytical-gradeDDAwasdissolvedindistilledwaterbyManyresearchersinvestigatethemechanismoffoamstability.adding50%(moleratio)aceticacid;thissampleislabeledasDDA.Theymostlyfocusedonthedynamics,involvingtheformationAnothersetofanalytical-gradeDDAwasdissolvedwithoutaceticacidofliquidfilmsandfoams,drainingfluidsoffoam,liquidfilmindistilledwaterat50°ConahotplateandlabeledasDDA(noAA).rupture,coarseningofbubbles,andinteractionbetweenUnlessspecifiedotherwise,“DDA”referstothesampledissolvedwith37−4037aceticacid.Analytical-gradeSDSwasdissolveddirectlyindistilledparticlesandbubbles.Listatedthatfoamdecayisaffectedbytwodrainageprocesses,namely,thethermodynamicwater.Analytical-gradehydrochloricacid(HCl)wasusedasapHdrainageoftheliquidfilmandthegravitydrainageintheplateauregulator.Deionizedwaterwasusedinallexperiments.border.Forthegravitydrainageintheplateauborder,(1)thegreaterthewatercontentinthefoam,thefasterthedrainage■METHODSspeed;(2)thegreatertheviscosityoftheliquid,theslowertheFrothStabilityExperiment.Thefrothstabilitywasevaluatedbydrainagespeed;and(3)thelowerthesurfacetensionoftheaeration.TheeffectofbothDDAandSDSconcentrationsaswellasliquid,theslowerthedrainagespeed.Severalstudiesalsotheirweightratioonfoamstabilitywasinvestigated.TheDDA(orreportedtheeffectsofvariousfactors,suchasinorganicSDS)solutionswithdifferentconcentrations(0.05,0.1,0.2,0.4,and1.0salts,41−45concentrationandtypesofsurfactants,46−49temper-wt%)wereprepared.Moreover,theweightconcentrationofDDAwithature,50particlesize,51,52hydrogenbonding,53andmoisture,54aceticacidwasfixedat0.2wt%,andthen,thecorrespondingSDSwasonfoamstability.DespitetheexistenceofextensiverelatedaddedaccordingtotestdesignbeforeregulatingthepHat4.ThemixedsolutionswithdifferentweightratiosofDDA:SDSwereprepared.research,thestudiesthatcoverthemicro-configurationoftheAfterward,thesolutionpreparedwithavolumeof200mLwasinjectedgas−liquidinterfaceanditsrelationshipwithfoamstabilityareintoanorganicglasstubeandaeratedfor10satanaerationrateof300scarce.mL/min.Finally,themaximumfoamheightwasrecordedafterNowadays,severalmethodsfortheconfigurationstudyofstandingfor10s.Thetimewhenthemaximumfoamheightdecreasedsurfactantsatthegas−liquidinterfacehavebeenreportedinthetohalfwasdefinedasthehalf-lifeperiod,whichwasusedtoinvestigate55−62thefoamstability.Thetestsunderthesameconditionswereconductedliterature,includingsurfacetensiontesting,X-rayreflec-tion,small-angleneutronscattering,neutronreflectivity,andthreetimes.vibrationalsum-frequencyspectroscopy.Nevertheless,theseSurfaceTensionAnalysis.AKRUSSsurfacetensionmeterwastraditionalexperimentalmethodssofar,however,sufferfromadoptedtomeasurethesurfacetension.Thesurfacetensionsofsolutionspreparedweremeasured.Thetestsunderthesameconditionsthefactthattheyaredifficulttopresentthemicro-configurationweredonethreetimes.Themeasuredtemperaturewasmaintainedatofsurfactantsatthegas−liquidinterface.Severalstudieshaveabout25°C.revealedthatthemoleculardynamics(MD)simulationToF-SIMSAnalysis.ToF-SIMSanalysis(IONTOFGmbH,technologycanobtainthestructureinformationanddynamicMünster,Germany)wasadoptedtocharacterizethegas−liquidsurfaceinformationofthegas−liquidinterface,whichisdifficulttoofdifferentsurfactantsolutions.1236https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

2Langmuirpubs.acs.org/LangmuirArticleDifferentsurfactantsolutionswereinjectedintoindividualopenglass(RDF),andthediffusioncoefficient(DC)ofwatermoleculesinthetankswithdimensionsofapproximately14×12×2mm3andfrozenatfirsthydrationlayerwereanalyzedusinganalysistoolsintheForcite−120°Cbyusingliquidnitrogenbeforetesting.TheToF-SIMSmodule.TheaverageanglesbetweenthemolecularchainsofDDA(orspectralacquisitionwasconductedwithin30minofthesampleSDS)andtheZ-axiswereinvestigatedusingscriptanalysis.Allpreparation.calculationswereperformedwiththeForciteprograminMaterials74AToF-SIMSVinstrumentwasusedtoobtainthedepthprofilesofStudio2017.COMPASSwasselectedastheforcefield,Smartmultilayerfilms.TheinstrumentequippedwithaBiandoxygenclusterMinimizerwasusedforgeometricaloptimization,andtheNVTiongunwasoperatedinthedual-beammode.A500eVoxygenclusterensemblewasusedtolimittheMDsimulationcalculation.Theionbeamwasusedforsputtering,anda30keVBi+analysisbeamwas3temperaturewascontrolledat298KusingtheAndersencontrolusedtoanalyzethecentralregionbetweenthesputteringpulses.method.TheEwaldmethodandatombasemethodwereusedtoMoreover,anelectronfloodgunwasadoptedforthechargecalculatetheelectrostaticandintermolecularinteractions,respectively.compensation.ThesamplewasexaminedwithaCs+ionbeamrasteredThetotalsimulationtimewas2000ps;thetimestepwas1fs,andoneovera400×400μm2areaandaBi+beamrasteredovera100×1003framewasoutputtedevery1000steps.μm2area;therasteringwasperformedinarandommodeovera256×256pixelareaandwasstoppedafter35s.Dataacquisitionandthe■subsequentdataprocessandanalysiswereperformedusingSurfaceLabRESULTSANDDISCUSSION6(IONTOF).FrothStability.TheeffectsofDDAandSDSconcentrationsComputationDetails.Inthispaper,thegas−liquidinterfaceofandtheirweightratiosonfoamstabilitywereinvestigated.foamwasstudiedusingtheSandwichmodel.CHNH+(Figure1a)12253Figure2ashowsthefrothhalf-lifeperiodofthesurfactantsasafunctionofDDAandSDSconcentrationsatpH4.Thefrothhalf-lifeperiodofDDAandSDSincreasesinitially,thenreachesthemaximumwhentheconcentrationisupto0.2wt%,andfinallydecreasesastheconcentrationfurtherincreases.Thefrothhalf-lifeperiodofDDAsignificantlyincreasesfrom981to2100min,andthatofSDSconsiderablyenhancesfrom298to860min,whentheconcentrationincreasesfrom0.05to0.2wtFigure1.Structuresoftheresearchobjects:(a)CHNH+and(b)%.Thefrothhalf-lifeperiodofDDAislongerthanthatofSDS;12253CHSO−.12253thefrothhalf-lifeperiodsofDDAandSDSataconcentrationof0.2wt%are2100and860min,respectively.andCHSO−(Figure1b)molecules,watermolecules,andAfterfixingtheconcentrationofDDAat0.2wt%,the12253counterions(CHCOO−andNa+)wereconstructedbyusingthecorrespondingSDSwasaddedinaccordancewithdifferent3SketchtoolinMaterialsStudio2017,andtheirchargedistributionandweightratios(DDA:SDS).TheeffectofSDSonthefrothhalf-preliminaryoptimizationwereconducted,respectively.ThestructureslifeperiodoftheDDAsolutionwasinvestigated.Figure2boftheresearchobjectsareshowninFigure1.indicatesthatwhentheDDAconcentrationislessthanacertainTheamorphouscellconstructiontoolandthebuildlayerstoolwerevalue,theadditionofSDScandecreasethefrothhalf-lifeperiodusedtoconstructthegas−liquidinterfaceoftheSandwichmodel.The−+ofthesolution.ThehighertheproportionofSDS,thelowerthecounterionsCH3COOandNa,whosenumberswerethesameas+−foamstabilityofthesolution.Inaddition,thefoamofthemixedthoseofC12H25NH3andC12H25SO3,respectively,wereaddedtothewaterboxrandomlytomaintaintheelectricalneutralityofthesystem.surfactantislessstablethanthatofthesinglesurfactant(DDAorTheoptimizedDDAs(orSDSs)wereplacedsymmetricallyontheSDS)whentheDDAconcentrationislessthanacertainvalue.interfaceofthewaterlayer.AllthecarbonchainsofDDA(orSDS)Figure2presentsthemaximumhalf-lifeperiodsofthemoleculeswereparalleltotheZ-axis.Thethicknessofthewaterlayerdifferentsolutions(DDA,SDS,andDDA+SDS).Similartrendswasatleast2nm,72,73whereasthatoftheselectedwatermoleculeswas75−78havebeenreportedfordifferenttypesofsurfactants.Before3.5nm.Thenumberofwatermoleculesaddedwas1000.Thedistancereachingthecriticalmicelleconcentration(CMC),asthebetweenthemonolayerandwaterwasmaintainedwithin0.2nm.A30surfactantconcentrationincreases,thesurfaceadsorptionÅvacuumlayerwasaddedtothemodelalongtheZ-axistoreducethecapacityincreases,thesurfacetensionsignificantlydecreases,periodicboundaryeffect.andcompactnessofthemoleculararrangementincreases.TheForcitemodulewasusedtooptimizethegeometricstructureofthemodelabove-mentioned,andthen,MDsimulationwascarriedoutConsequently,thefoamstabilityisenhanced.Moreover,bubblefortheoptimizedmodeltoobtaintheequilibriumconfiguration.Thecoalescenceisreducedandinterfacialelasticityisincreasedrelativeconcentrationdistributions,theradialdistributionfunctionbecauseofthestabilizationoffoamlamellaebymoleculesoftheFigure2.(a)Frothhalf-lifeperiodasafunctionofDDAandSDSconcentrationsand(b)effectofSDSonthefrothhalf-lifeperiodofDDAatpH4.1237https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

3Langmuirpubs.acs.org/LangmuirArticleFigure3.Surfacetensionsofthe(a)DDA,(b)SDS,and(c)DDA+SDSsolutionsand(d)theirbubblesizes.79surfactant.However,theincreaseinfoamstabilityisfoundshowsthattheCMCofthemixedsurfactantis0.4wt%,whichisonlyuptoaspecificconcentration.AfurtherincreaseinhigherthanthatofDDA.ThisincreaseinCMCmightcausethe76maximumhalf-lifeperiodtodeclineandshiftstoahigherDDAsurfactantconcentrationincreasesthecollapserateoffoam.ThedecreaseinfoamstabilityatsurfactantconcentrationsconcentrationwiththeincreaseintheratioofSDSintheDDA+abovetheCMCcanbeattributedtotheformationofmolecularSDSsolution(Figure2b).aggregates(micelles)attheCMCofthesurfactant.WangandTheamountofexcesssubstanceonthesurfacecanbeMulligan77,78relatedthedecreaseinstabilityoffoamathigherdeterminedusingtheGibbsadsorptionisothermequationconcentrations(>CMC)withtheincreasedweight(gravita-(Formula1).Thecross-sectionalarea(CSA)oftheadsorbed1tionaleffect)offoambecauseofexcessmoleculesofthemoleculesiscalculatedusingFormula2basedontheresultssurfactantatthelamella.BecauseoftheexcessofthesurfactantpresentedinFigure3a,b.ThefindingsrevealthattheCSAofSDS(2.61nm2)atthegas−liquidinterfaceislargerthanthatofmolecules,theimpactofgravitationonthedrainageoffoamDDA(1.39nm2).Thisresultisconsistentwiththemolecularincreased,whichresultedincontinuousliquiddrainagefromthefilmformedbetweenadjacentbubbles,eventuallyrupturingtheresultsobtainedfromthestructuraloptimizationinMaterialsliquidfilmstoresultinbubblecoalescence.80Beheraetal.81alsoStudio(Figure2).ThisfindingalsoexplainswhytheCMCofsuggestedthattherateofcollapseincreasedathigherDDAishigherthanthatofSDSconcentrationsduetoadecreaseinlamellaelasticitywhichcijjdσyzzdecreasedwithanincreaseinsurfactantconcentrationandledtoΓ=−jzRTkdc{T(1)fastfoamcollapse.Moreover,Figure2bshowsthatthemaximumhalf-lifeperioddecreasesandshiftstoahigherwhereΓistheamountofexcesssubstanceonthesurface,mol·DDAconcentrationwiththeincreaseintheratioofSDSinthem−2;cistheconcentration,mol/L;Risthegasconstant,8.314DDA+SDSsolution.ThisphenomenoncanbeattributedtothePa·m3/mol·K;andTisthethermodynamictemperature,KincreaseinCMCduetotheincreaseintheratioofSDS(Figure13c).Figure3cindicatesthattheCMCofthemixedsurfactantA=(DDA/SDS=1:0.25)is0.4wt%.Moreover,thefoamofthisΓ∞NA(2)mixedsurfactantexhibitsamaximumhalf-lifeperiodatthiswhereAistheCSAofadsorbedmolecules,m2;Γistheamount∞concentration.ofexcesssubstanceatasaturatedsurface,mol·m−2;andNistheASurfaceTensionandCross-SectionalAreaoftheAvogadroconstant,6.02×1023.AdsorbedMolecules.ThesurfacetensionsasafunctionofThesurfacetensionsofdifferentsolutionsatpH4areshownDDAandSDSconcentrationsaredepictedinFigure3a,b.TheinFigure3d.WhentheDDAconcentrationisfixedat0.2wt%,surfacetensiondecreasesinitiallyastheDDA(orSDS)theadditionofSDS(DDA/SDS=1:0.25)canimprovetheconcentrationincreases,thenreachesaminimum,andfinallysurfacetensionofthesolutionfrom24.81to27.39mN/m.increasesslightlyastheconcentrationfurtherincreases.ItMoreover,thesurfacetensionofSDSishigherthanthatofreachestheminimumwhentheconcentrationsofDDAandSDSDDA,whichmaybetheoneofthereasonswhySDSfoamislessreach0.2and0.1wt%,respectively.TheseresultsindicatethatstablethanDDAfoam(Figure1a).Inaddition,thefoamsinthetheCMCsofDDAandSDSare0.2wt%(1.1×10−2mol/L)SDS,DDA,andDDA+SDSsolutionswereexaminedusingaand0.1wt%(0.35×10−2mol/L),respectively.Liuetal.82microscopeunderthesamemagnification,andtheaveragereportedthattheCMCofDDAis1.2×10−2mol/L.Figure3cnumbersandsizesofbubblesweremeasuredusingImage-J1238https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

4Langmuirpubs.acs.org/LangmuirArticleFigure4.NormalizedpeakintensitieswithP=95%confidenceintervalsfromthe(a)positiveionand(b)negativeionsofdifferentsolutionsfrozenat−120°Cbyusingliquidnitrogen.software.TheorderofaveragebubblenumbersisDDA>DDAmainlycausedbythefactthattheCSAofSDSistwicelarger+SDS>SDS,andtheorderofaveragebubblesizesisDDADDA+SDS>DDA(noAA).velocity.DifferenttypesofsurfactantshavebeenexaminedbyAddingSDStotheDDAsolutionwilllessentheadsorptionof85Sardeingetal.,andtheyobservethatthebubblediameterDDAmoleculesatthegas−liquidinterface.Theresultsareindecreasesfromwatertoanionic,tocationic,andthentonon-goodagreementwiththesurfacetensionresults.ionicsurfactants.ThebubblesizesandthesurfacetensionFigure4bshowsthenormalizedpeakintensitieswithP=95%resultswehaveobtainedareconsistentwiththeseresultsabove-confidenceintervalsfromthenegativeionofdifferentsolutionsmentioned.frozenat−120°Cbyusingliquidnitrogen.AscanbeseenfromToF-SIMSanalysis.ToclearlydepictthedifferenceoftheFigure4b,theionsignalsofCH−,CN−,andCNO−weregas−liquidinterfacebetweenDDA+SDSandDDAandobservedatthegas−liquidinterfaceintheDDA(noAA),DDA,illustratetheeffectofSDSonthegas−liquidinterfaceoftheandDDA+SDSsolution.Thesepeaksarealsothefingerprintlatter,theDDAwithoutaceticacid[DDA(noAA)]wasalsopeaksofDDA.Inaddition,theionsignalsofO−,OH−,HO−,22analyzedusingToF-SIMS.ThesamplesanalyzedthroughToF-HO−,HO−,HO−,HO−,HO−,HO−,HO−,HO−,2232435344647484SIMSincludeDDA(noAA)(pH4,weightconcentration=HO−,HO−,HO−,andHO−wereobserved.Thesepeaks946585950.2%),DDA(pH4,weightconcentrationofDDA=0.2%,arethefingerprintpeaksofwater.Moreover,theionsignalsofconcentrationofaceticacid=1.1×10−2mol/L),andDDA+CHSO−andCHSO−werefoundatthegas−liquid1225414294SDS(pH=4,weightconcentrationofDDAandSDS=0.2%+interfaceintheDDA+SDSsolution.Thisfindingindicatesthat0.05%,concentrationofaceticacid=1.1×10−2mol/L).theSDSmoleculescanalsoadsorbatthegas−liquidinterfaceToF-SIMSSpectraAnalysis.Figure4ashowstheafteraddingSDStotheDDAsolution.TheadsorptionofSDSnormalizedpeakintensitieswithP=95%confidenceintervalsmoleculeswithaCSAthatisapproximately2timeshigherthanfromthepositiveionofdifferentsolutionsfrozenat−120°CbythatofDDAmoleculescausessomeofthelattertoentertheusingliquidnitrogen.TheionsignalsofNH+,CHN+,CH+,solutionandformmicelles,therebyreducingtheadsorption4425CH+,CH+,CHN+,CHN+,CHN+,CHN+,andcapacityoftheDDAmoleculesatthegas−liquidinterface.49373681810221227CHN+wereobservedonthegas−liquidinterfaceinDDAWhat’smore,itisfoundthatcomparedwiththeDDAandDDA1228(noAA),DDA,andDDA+SDSsolution.Thesepeaksarethe+SDSsolutions,DDAmulti-molecularpeaks(CHN−,14302fingerprintpeaksofDDA.TheorderofpeakintensityrelatedtoCHN−,andCHN−)intheDDA(noAA)solutionwere1432214332DDAisDDA>DDA+SDS>DDA(noAA).Thisfindingclearlyobservedatthegas−liquidinterface,indicatingthatDDAimpliesthattheDDAadsorptioncapacityatthegas−liquidwithoutaceticacidcannoteasilyinteractwithwater,whichareinterfaceisweakwithoutaceticacid;theadditionofaceticacidislikelytounitetogether.Inaddition,theCHNO−and2beneficialtotheadsorptionofDDAattheinterface.Moreover,CHNO−signalionpeakswerefoundatthegas−liquid5132theresultsindicatethataddingSDStotheDDAsolutionwillinterfaceoftheDDAsolutionwithaceticacid.ThetwosignallessentheadsorptionofDDAatthegas−liquidinterface.InionpeaksarecausedbythestronginteractionbetweenDDAandaddition,theionicpeakintensityassociatedwithDDAintheaceticacidaftertheadditionofthelatter,whichresultsintheDDAsolutionistwicethatintheDDA+SDSsolution(FigureformationofCOO···NHandCOO···4a).ThisfindingindicatesthattheadsorptioncapacityofDDANH3CH2CH2CH2CH2CH2.ThetwoionicpeakswerehardlyintheDDAsolutionisroughlytwicethatintheDDA+SDSobservedatthegas−liquidinterfaceoftheDDA(noAA)andsolution.TheseresultsillustratethatwhentheDDADDA+SDSsolutions.ThisfindingsuggeststhataddingSDStoconcentrationisfixed,theadditionofSDSwillcausethehalftheDDAsolutionwithaceticacidcanreducetheadsorptionofofDDAmoleculestomigratetothesolutionandformmicelles.CHCOO−ionsatthegas−liquidinterface.Suchareduction3AccordingtotheresultsoftheadsorptionmolecularCSA,thisiscanbeascribedtothestrongelectrostaticinteractionbetween1239https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

5Langmuirpubs.acs.org/LangmuirArticleFigure5.(a)ScoresonPCs1and2andloadingsfor(b)PC1and(c)PC2fromthePCAofthepositive-ionspectraofdifferentsolutionsfrozenat−120°Cbyusingliquidnitrogen.Figure6.DepthprofileoftheDDAsolutionswithandwithoutaceticacidfrozenat−120°Cbyusingliquidnitrogen:(a)positiveionand(b)negativeion.SDSandDDA,whichinhibitstheinteractionbetweenDDAandPC1isthemaindistinctionbetweentheBsampleandotherCHCOO−andcausessomeCHCOO−ionstomigratefromsamples(AandC).ThepeaksCHN+,CHN+,andCHN+331228425theinterfacelayertotheliquidphase.Thisphenomenonresults(positivePC1loadings),whicharerelatedtoDDAmolecules,inthedecreaseinCHCOO−ionsatthegas−liquidinterface.areattributedtoDDAwithaceticacidatpH4(positivePC13TheCHCOO−ionsatthisinterfacecanformadoubleelectricscores),whilethepeaksOH+,OH+,OH+,OH+,and3254937511layerwiththesurface.Whentheliquidfilmbecomesthin,theHO+(negativePC1loadings),whicharecorrelatedtothewater3mutualrepulsionforcebetweenitstwosurfacesweakens.Thismolecules,areassignedtoothersamples(negativePC1scores).phenomenonisnotconduciveinpreventingtheliquidfilmfromThePC1loadingsreflectthenegativecorrelationbetweenthethinningfurtheranddecreasesthefoamstability.Theseresultswater-relatedpeaksandDDAspecies-relatedpeaks.Meanwhile,corroboratewellwiththefoamstabilityresults.inthescoreplot,theCsample[c(DDA)=0.2wt%]hasthePositive-andNegative-IonSpectraAnalysisthroughmaximumpositivePC1score.Therefore,theresultsofPC1PrincipalComponentAnalysis.Figure5showsthescoresindicatethattheorderoftheDDAadsorptioncapacityattheandloadingsfromtheprincipalcomponent(PC)analysisgas−liquidinterfaceisDDA(noAA)

6Langmuirpubs.acs.org/LangmuirArticleFigure7.DepthprofileoftheDDAandDDA+SDSsolutionsfrozenat−120°Cbyusingliquidnitrogen:(a)positiveionand(b)negativeion.Figure8.RelativeconcentrationsofdifferentcomponentsalongtheZ-axis:(a)DDA,(b)SDS,and(c)DDA+SDS.interfacetendstobelessuprightafteraddingSDStotheDDAOH−ionpeakintensityrelatedtowaterinDDAsolutionswithsolution.ThisspeculationwillbeverifiedthroughMDandwithoutaceticacidgraduallyincreasesasthesputtertimesimulation.increases.FortheDDAsolutionwithaceticacid,theCHNO−2DepthProfilingAnalysis.TheDDAsolutionswithandandCHNO−ionpeakintensitiesgraduallydecreaseasthe5132withoutaceticacidfrozenat−120°Cbyusingliquidnitrogensputtertimeincreases,whereastheCHN−ionpeak14322weresubjectedtodepthprofiling.Thedepthprofileresultsofintensityisextremelylowanddemonstratesaminimalchange.DDAsolutionsfrozenbyusingliquidnitrogenareshowninFortheDDAsolutionwithoutaceticacid,theCHNO−and2Figure6.−+++C5H13NO2ionpeakintensitiesareextremelylowandexhibitaTheintensitiesoftheC2H5,C12H27N,andC12H28Nionminimalchangewiththeincreaseinsputtertime,whereasthesignals,whichareknownasthemarkersofDDA,decreasefirst−C14H32N2ionpeakintensitydemonstratesagradualdecline.andthenslightlychangeasthesputtertimeincreases(Figure+Theseresultsfurthersupporttheinferencethattheadsorption6a).Moreover,theintensityoftheCsO2H4ionsignalrelatedtocapacityofDDAatthegas−liquidinterfaceoftheDDAsolutionwaterincreasesfirstbeforedisplayingnosignificantchange.withoutaceticacidisweak.Moreover,thesemoleculescannotComparedwiththeDDAsolutionwithaceticacid,theintensitiesoftheionpeaksrelatedtoDDAintheDDAsolutioneasilyinteractwithwaterandarelikelytoagglomeratetogetherwithoutaceticacidarelow,whereasthoseoftheionpeaksduetotheattractiveforcesamongtheDDAmolecules.Afterrelatedtowaterarehigh.ThisresultsuggeststhatwithoutaceticaddingaceticacidtotheDDAsolution,astronginteractionacid,theDDAmoleculescannoteasilyadsorbatthegas−liquidbetweenDDAandaceticacidoccurs,andtheadsorptioninterface.capacityofDDAatthegas−liquidinterfacesubsequentlyFigure6bshowsthenegative-ionpeaks(OH−,CHNO−,increases.TheconcentrationofDDAgraduallydecreasesfrom2CHNO−,andCHN−)asafunctionofsputtertime.Thethegas−liquidinterfacetothesolutionphase.5132143221241https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

7Langmuirpubs.acs.org/LangmuirArticleFigure9.(a)RDFoftheDDAandSDSheadgroupsandwatermoleculesand(b)MSDofwatermoleculesinthefirsthydrationlayer.Figure7showsthedepthprofileresultsoftheDDAandDDAFigure8billustratesthatSDScanassembleatthegas−liquidinterface,thepolarheadgroups(−SO−)areimmersedinthe+SDSsolutionsfrozenat−120°Cbyusingliquidnitrogen.3Figure7aillustratesthattheintensitiesoftheCHN+andaqueousphase,andmostcarbonchainsarefoundinthegas1227+phase.Inaddition,thecounterions(Na+)mostlygatheraroundC12H28Nionpeaks,whicharerelatedtoDDA,decreasefirstandthenslightlychangewiththeincreaseinthesputtertime.theheadgroupsofSDSowingtotheelectrostaticinteractionbetweenthecounterions(Na+)andheadgroups(−SO−).ThepeakintensitiesrelatedtoDDAintheDDA+SDSsolution3arelowerthanthoseintheDDAsolution.Incontrast,thepeakFromFigure8c,itcanbeseenthatDDAandSDScanintensitiesrelatedtowaterintheformerarehigherthanthoseinassembleatthegas−liquidinterface.Additionally,thepolarheadgroups(−NH+and−SO−)areimmersedintheaqueousthelatter.ThisresultshowsthataddingSDStotheDDA33solutioncanreducetheadsorptioncapacityofDDAatthegas−phase,andmostcarbonchainsarefoundinthegasphase.liquidinterface.Moreover,comparedwiththeresultsfromFigure8a,b,itisThenegative-ionpeaks(OH−,CHNO−,CHNO−,andfoundthatafteraddingSDStotheDDAsolution,most25132−+CHSO−)asafunctionofsputtertimearedepictedinFigureCH3COOandNamovefromtheinterfacetothesolution.122547b.TheOH−ionpeakintensityrelatedtowaterintheDDAandThisresultissupportedbyToF-SIMSresults.TheseresultsDDA+SDSsolutionsgraduallyincreasesasthesputtertimeabove-mentionedindicatethattheadditionofSDStotheDDAincreases.Withtheincreaseofthesputtertime,theCHNO−solutioncangreatlyreducetheadsorptionofcounterions2−+andCHNO−ionpeakintensitiesintheDDAsolutionwith(CH3COOandNa)atthegas−liquidinterface,whichresults5132inthemovementofthesecounterionsfromtheinterfacephaseaceticaciddecreasegradually,whereasitisdifficulttofindthesetothesolutionphase.peaksintheDDA+SDSsolution.TheseresultsindicatethatWhentherelativeconcentrationofwatermoleculesgraduallyafteraddingSDStotheDDAsolution,theinteractionbetweendecreasesto0fromtheliquidphasetothegasphase,theregiontheaceticacidionandDDAisweakened.wherethewaterdensitydecreasesistheinterlayer.TheMDSimulationResults.Theresultsofsurfacetensionandinterlayerthicknessofthegas−liquidinterfaceisdefinedasToF-SIMSanalysesindicatethataddingSDStotheDDAthedistancewherethewaterdensitydecreasesfrom90to10%.solutioncanreducetheadsorptioncapacityoftheDDAThethicknessvaluesintheDDA,SDS,andDDA+SDSmoleculesatthegas−liquidinterface.WhentheDDAsolutionsare16.14,15.15,and14.07Å,respectively.Theconcentrationisfixed,theadditionofSDS(weightconcen-thicknessintheSDSsolutionissmallerthanthatintheDDAtrationratio,DDA/SDS=1:0.25=4:1;moleratio,DDA/SDS=solution,whichmightbeanotherreasonwhythefoamstability6:1)causeshalfoftheDDAmoleculestoenterthesolutiontoofthelatterishigherthanthatoftheformer(Figure1a).Informmicelles.Inthisstudy,36CHNH+representstheDDA12253addition,comparedwiththeDDAsolution,theinterlayersolution,whereas18CHNH+and6CHSO−denotethe1225312253thicknessofthegas−liquidinterfacedecreasesafteraddingSDSDDA+SDSsolution.ThecounterionsCHCOO−andNa+,3totheDDAsolutionandthusleadstoadecreaseinfoamwhosenumbersarethesameasthoseofCHNH+and12253stability.TheresultscorroboratewellwiththefoamstabilityCHSO−,respectively,areaddedtothewaterboxrandomly12253results.tomaintaintheelectricalneutralityofthesystem.InteractionbetweenSurfactantsandWaterMole-MonolayerPropertiesofDDA.Afterequilibrium,thecules.TheRDFofwatermoleculesaroundthehydrophilicrelativeconcentrationdistributionsofdifferentcomponentsheadgroupswasanalyzedtoinvestigatetheinteractionbetweenalongtheZ-axis(perpendiculartothegas−liquidinterface)arereagentandwatermoleculesandfoamstability.ItisobservedshowninFigure8.AsrepresentedinFigure8a,DDAcanfromFigure9athatthefirstobviouspeakbetweenDDAandaccumulateatthegas−liquidinterface,thepolarheadgroupswatermoleculesappearsnear3.5ÅandthatbetweenSDSand(−NH+)areimmersedintheaqueousphase,andmostcarbon3watermoleculesappearsnear4.2Å.Thisresultshowsthatachainsarefoundinthegasphaseowingtotheirstrongstronginteractionbetweentheheadgroups(−NH+or−SO−)33hydrophobicity.Additionally,thecounterions(CHCOO−)3andwatermoleculesoccurs,andahydrationlayeraroundthemostlygatheraroundtheheadgroupsofDDAduetotheirheadgroupforms.Therangewithinthepeakvalleyofthefirstsimilarpeakpositions.Theresultisduetotheelectrostatic65peakiscalledthefirsthydrationlayer.Figure9bshowstheinteractionbetweenthecounterions(CHCOO−)andhead3meansquaredisplacement(MSD)ofwatermoleculesatthefirstgroups(−NH+),resultinginthemovementofcounterions3hydrationlayerunderdifferentconditions.Themovementfromtheaqueousphasetotheinterface.abilityofmoleculesisprimarilyreflectedbytheirDCs.TheDC1242https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

8Langmuirpubs.acs.org/LangmuirArticleFigure10.(a)RDFoftheheadgroupsofthesurfactants,(b)schematicoftheanglebetweenthesurfactantmolecularchainandtheZ-axis,and(c)angleresults.Figure11.EffectofSDSonadsorptionconfigurationofDDAatthegas−liquidinterface:thegas−liquidinterfacesof(A1)DDA(withaceticacid),(B1)SDS,and(C1)DDA(withaceticacid)+SDSsolution;thefoammorphologiesof(A2)DDA(withaceticacid),(B2)SDS,and(C2)DDA(withaceticacid)+SDSsolutionatthemacrolevel.65isequalto1/6oftheslopeoftheMSDcurve.TheDCsofconditions(Figure10a)wereanalyzedtoinvestigatethewatermoleculesatthefirsthydrationlayeraroundtheheadinteractionbetweenthepolarheadgroupsofDDAandSDS.group(−NH+or−SO−)intheDDAandSDSsolutionsareTheangledistributions(Figure10c)betweentheDDA(or330.29and0.28,respectively.However,intheDDA+SDSSDS)moleculechainandtheZ-axisindifferentsurfactantsolution,theDCsofwatermoleculesaroundtheheadgroupssystemswerealsoanalyzed.Aschematicoftheanglebetween−NH+andtheheadgroups−SO−increaseto0.33and0.31,theDDA(orSDS)moleculechainandtheZ-axisisshownin33respectively.TheresultsindicatethatafteraddingSDStotheFigure10b.DDAsolution,theinteractionbetweenwatermoleculesandtheAsshowninFigure10a,theaveragedistanceamongtheNandheadgroups(−NH+or−SO−)isweakened,andtheSatomsoftheDDAandSDSheadgroups,respectively,33movementabilityofwatermoleculesaroundtheheadgroupsincreasesafteraddingSDStotheDDAsolution.Thisincreaseisstrengthened.ThesewatermoleculesareeasytoloseinthecanbeattributedtothelargerCSAofSDSatthegas−liquiddrainingfluidprocess,therebydecreasingthefrothstability.TheinterfacecomparedwiththatofDDA.Thisdiscrepancyresultsresultsareconsistentwiththeresultsoffrothstability.inadecreaseintheadsorptioncapacityoftheDDAandtotalConfigurationsofReagentMoleculesattheGas−moleculesinthegas−liquidinterfaceaswellasinarelativelyLiquidInterface.TheRDFsofNatomsintheDDAheadsparsemoleculararrangement,whichdecreasethefrothstability.groupsandSatomsintheSDSheadgroupsunderdifferentFigure10cshowsthatintheDDA+SDSsystem,theaverage1243https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

9Langmuirpubs.acs.org/LangmuirArticleanglebetweentheDDA(SDS)molecularchainandtheZ-axisismutualrepulsionforcebetweenthetwosurfacesofthe45.35°(44.98°).ComparedwiththeDDAorSDSsystem,theliquidfilm.Furthermore,theadditionofSDScausedaaverageanglebetweenthemolecularchainandtheZ-axissparseandlessuprightarrangementofmolecules,whichincreases.Thegreaterthisangle,thesmallerthedistanceenhancedthepermeationofthegasandconsequentlybetweenthemoleculartailchainandthegas−liquidinterfacedecreasedthefoamstability.andthesparserthemoleculararrangement.Furthermore,thepermeationofthegasisenhanced,therebydecreasingthefoamstabilitytoacertainextent.Theresultsareconsistentwiththe■AUTHORINFORMATIONfoamstabilityandTOF-SIMSresults.TheeffectofSDSontheadsorptionconfigurationofDDAinCorrespondingAuthorthegas−liquidinterfaceisdepictedinFigure11.A1,B1,andC1YunfanWang−StateKeyLaboratoryofComplexNonferrousrepresentthegas−liquidinterfacesofDDA(withaceticacid),MetalResourcesCleanUtilizationandFacultyofSDS,andDDA(withaceticacid)+SDSsolution,respectively.MetallurgicalandEnergyEngineering,KunmingUniversityofA2,B2,andC2arethecorrespondingfoammorphologiesattheScienceandTechnology,Kunming650093,China;macrolevel.TheadditionofSDScandecreasetheDDAorcid.org/0000-0003-4393-7015;Email:asc_cloud@adsorptionatthegas−liquidinterfaceandcausesomeDDA163.commoleculestomigratetothesolutionandformmicelles.Thisphenomenonleadstotheincreaseinsurfacetension.Moreover,AuthorsaddingSDScandecreasethegas−liquidinterfaciallayerXimeiLuo−FacultyofLandandResourceEngineeringandthicknessandenhancethemovementabilityofthewaterStateKeyLaboratoryofComplexNonferrousMetalResourcesmoleculesaroundtheheadgroupsofthesurfactants.CleanUtilization,KunmingUniversityofScienceandFurthermore,suchanadditiongreatlydecreasestheinteractionTechnology,Kunming650093,ChinabetweentheheadgroupsofDDAandSDSandtheirQiqiangLin−FacultyofLandandResourceEngineering,correspondingcounterions(CHCOO−andNa+,respectively)KunmingUniversityofScienceandTechnology,Kunming3atthegas−liquidinterface.Asaresult,thecounterionsmigrate650093,Chinafromtheinterfacephasetothesolutionphase,therebyShumingWen−FacultyofLandandResourceEngineeringandweakeningthemutualrepulsionforcebetweenthetwosurfacesStateKeyLaboratoryofComplexNonferrousMetalResourcesoftheliquidfilm.TheadditionofSDSalsocausesasparseandCleanUtilization,KunmingUniversityofScienceandlessuprightarrangementofmolecules,whichenhancestheTechnology,Kunming650093,ChinapermeationofthegasandconsequentlydecreasesthefoamHaoLai−FacultyofLandandResourceEngineering,Kunmingstability.UniversityofScienceandTechnology,Kunming650093,China■LinpingQi−FacultyofLandandResourceEngineering,CONCLUSIONSKunmingUniversityofScienceandTechnology,KunmingTheobjectiveofthisstudyistoinvestigatetheeffectofSDSon650093,ChinathefoamstabilityoftheDDAsolutionandonitsadsorptionXuetongWu−FacultyofLandandResourceEngineering,configurationatthegas−liquidinterface.TheresultsoftheKunmingUniversityofScienceandTechnology,Kunmingsurfacetensiontests,ToF-SIMSmeasurements,andMD650093,ChinasimulationprovidedusefulknowledgeonwhySDSdecreasesYongfengZhou−FacultyofLandandResourceEngineering,thefoamstabilityoftheDDAsolution.KunmingUniversityofScienceandTechnology,Kunming(1)ThefrothstabilityoftheDDAsolutionwasextremely650093,Chinastrong.AddingacertainamountofSDScoulddecreaseZhenguoSong−StateKeyLaboratoryofMineralProcessingthefoamstability.ThefoamstabilityofthemixedScienceandTechnology,BGRIMMTechnologyGroup,Beijingsurfactant(DDA+SDS)waslowerthanthatofthesingle100160,Chinasurfactant(DDAorSDS).Completecontactinformationisavailableat:(2)Theresultsofthesurfacetensiontests,ToF-SIMShttps://pubs.acs.org/10.1021/acs.langmuir.0c03248measurements,andMDsimulationindicatedthattheCSAofSDSinthegas−liquidinterfacewaslargerthanNotesthatofDDA.Therefore,theadditionofSDScouldTheauthorsdeclarenocompetingfinancialinterest.decreasetheDDAadsorptionattheinterfaceandcausesomeDDAmoleculestomigratetothesolutionandform■micelles.ThisphenomenonledtotheincreaseinsurfaceACKNOWLEDGMENTStension.AddingSDScouldreducethegas−liquidTheauthorsgratefullyacknowledgethefinancialsupportfrominterfaciallayerthickness,weakentheinteractiontheNationalNaturalScienceFoundationofChina(grantnos.intensitybetweentheheadgroupsofthesurfactants51964025and51604130),theTenThousandTalentsPlanforandwatermolecules,andenhancethemovementabilityYoungTop-notchTalentsofYunnanProvince(YNWR-QNBJ-ofthewatermoleculesaroundtheheadgroups.2018-167),theOpenFundProjectoftheStateKeyLaboratoryMoreover,suchanadditiongreatlydecreasedtheofMineralProcessingScienceandTechnology(BGRIMM-interactionbetweentheheadgroupsofDDAandSDSKJSKL-2019-05),andtheFundProjectoftheAnalyticalandandtheircorrespondingcounterions(CHCOO−and3TestingResearchCenterofKunmingUniversityofScienceandNa+,respectively)atthegas−liquidinterface,therebyTechnology(2020T20140027).Additionally,theauthorsresultinginthemigrationofthecounterionsfromthewouldliketoexpresstheirgratitudetoeditorsandreviewersinterfacephasetothesolutionphase,whichweakenedthefortheirdiligentwork.1244https://dx.doi.org/10.1021/acs.langmuir.0c03248Langmuir2021,37,1235−1246

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