Interfacial and Emulsion Characteristics of Oil − Water Systems in the Presence of Polymeric Lignin Surfactant - Ghavidel, Fatehi - 2021

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pubs.acs.org/LangmuirArticleInterfacialandEmulsionCharacteristicsofOil−WaterSystemsinthePresenceofPolymericLigninSurfactantNasimGhavidelandPedramFatehi*CiteThis:Langmuir2021,37,3346−3358ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Itishypothesizedthatpolymericligninsurfactantshavedifferentaffinitiesforstabilizingoil−wateremulsionsandthattheemulsifyingperformanceofthesesurfactantsishighlyaffectedbytheiradsorptionperformanceattheoil−waterinterface.Tovalidatethishypothesis,theadsorptionperformanceofsulfethylatedlignin(SEKL)surfactantatdifferentoil−waterinterfaceswasexaminedbyassessingthecontactangle,dynamicinterfacialtension,andsurfaceloading(Γ).Moreover,theinterfacialadsorptionkineticsofSEKLwascompre-hensivelyassessedindifferentoil−watersystemstorevealthemechanismsoftheSEKLadsorptionattheinterface.Also,theimpactsofSEKLconcentrationandionicstrengthontheperformanceofSEKLasaneffectiveemulsifierfortheemulsionswereassessed.Furthermore,thedropletsizeandinstabilityindexoftheemulsionsweresystematicallycorrelatedwiththeadsorptionperformanceofSEKLattheinterfaceofoilandwater.Forthefirsttime,byimplementingamodifiedWardToradaidiffusionmodel,twodistinctearlystagesoftheadsorptionofSEKLattheoilinterfacewereidentified.Interestingly,thesecondstagewasthedeterminingstageofadsorptionwiththediffusion-controlledmechanismwhenpolymersreconfiguredattheoil−waterinterface.SaltscreeningfacilitatedtheclusteringofSEKLuponchargerepulsionelimination,whichremovedtheenergybarrierinthefirststageofadsorption(ΔEp→0=0),butitintroducedastericbarrieruponthereconfigurationofpolymersattheoilinterfacesinthesecondstageofadsorption.Inadditiontothekineticsofadsorption,satisfactorycorrelationswereobservedbetweensurfacepressure(Δγ=γ∞−γ0),surfaceloading(Γ)ofpolymers,andcontactangleatoilinterfacesononehandandtheoildropletsizeandemulsionstabilityontheotherhand.1.INTRODUCTIONRecently,substantialattentionwasdevotedtoexploringtheBio-basedpolymericmaterialssuchaslignocelluloses,starch,interfacialbehaviorofnatural-basedemulsifiers,including17181920andchitosanhaveattractedsubstantialinterestduetotheircellulose,proteingranules,starch,andchitosan,withDownloadedviaUNIVOFNEWMEXICOonMay16,2021at10:36:11(UTC).1−4differenttechniques,suchasinterfacialshearrheology,greatbiocompatibility,biodegradability,andrenewability.Theyareappliedassolubilizers,thickeners,andstabilizersforellipsometry,anddynamicinterfacialtensiometry,tofurtheremulsionsystemsduetotheirinherentfeatures,suchasdeterminetheirroleinemulsionstability.Forinstance,WeietSeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.19multiplefunctionalgroups,complexconformationalchangesatal.proposedacorrelationbetweeninterfacialrheological5,6theoilinterface,andviscosityenhancement.propertiesofesterifiedfibergum(CFG)anditsemulsionWater-solubleligninderivativescanbeusedasemulsifyingstability.Inanotherstudy,thesurfaceloadingofstarchwasagentstoreducetheinterfacialtensionbetweenoilandwaterdeterminedbydual-wavelengthmethodstoformacompactandstabilizeliquid−liquidmixturesbyformingstericemulsifierlayerattheoilinterfaceofn-hexane.21Theimpacts7,8interfacialfilms.Forinstance,functionalizedwater-solubleofstructuralandchemicalpropertiesofproteinsonthe9,10ligninderivatives,includingcarboxymethylatedlignin,kraftinterfacepropertiesofoil−waterinterfaceswerealso1112lignin-tannicacid,sulfethylatedlignin,andpolyacrylamide-evaluated.14,22,23Inourpreviousstudy,theuseofsulfethylated13graftedligninhavebeenreportedasefficientstabilizersforlignin(SEKL)asapolymericsurfactantwasexamined,andtheemulsionformation.Currently,methodsforthecharacter-izationofemulsionsusingligninderivativesmainlyinvolvetheanalysisofdestabilization,dropletsize,andtherheologicalReceived:December3,2020characterizationoftheemulsions.9−13InadditiontosuchRevised:February1,2021analysis,theknowledgeofthekineticsofadsorbedmassatthePublished:March5,2021interfaceofoilandwatercanshedlightonunderstandingtheroleofemulsifiersinsuchemulsionsystems,especiallyintheir14−16long-termstability.©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c034583346Langmuir2021,37,3346−3358

1Langmuirpubs.acs.org/LangmuirArticle1212h.Thedriedproduct,SEKL,wasobtainedaftertheevaporationoffocuswasonformingaPickeringstabilizeratalteredpH.However,thefundamentalimpactsofSEKLontheinterfacialwaterintheovenat105°C.propertiesandemulsionstabilityofoil−wateremulsionshave2.3.HydrodynamicSizeAnalysis.Adynamiclightscatteringnotbeenevaluated.analyzer(BI-200SMBrookhavenInstrumentsCorp.,UnitedStates)equippedwitha35mWlaserpowersourcewasusedtoobtaintheThemainobjectiveofthisstudywastofurtherunderstandhydrodynamicdiametersofSEKL.SolutionsofSEKLat0.8wt%inatheadsorptionbehaviorandinterfacialpropertiesoftheSEKLsalt-freesystemand10and100mMKClsolutionswerepreparedatatdifferentoil−waterinterfaces.Inthiswork,decane,pH7.Afterstabilizingfor24h,thesolutionswerefilteredbycyclohexane,andxylenewerechosenasoilphasestoexploreWhatmanfilterswithaporesizeof0.45μm.TheRhdistributionofthetendencyofSEKLforstabilizingvariousoil−waterthesampleswasdeterminedatthewavelengthof637nmwitha24,25scatteringangleof90°at25°C.emulsions.Topredictandevaluatethecompatibilityandinterfacial2.4.ContactAngleAnalysis.ThecontactanglesofSEKLadsorptionkineticsofSEKLatdifferentoil−waterinterfaces,polymersattheair−water(WCA)andoil−water(OCA)interfacesthecontactangleofSEKLatwaterandoilinterfacesandweredeterminedintwodifferentexperiments.Initially,theSEKLsolutionof0.8wt%atpH7wascoatedonglassslidesusingaspindynamicinterfacialtension(γ)weremeasured.Fromthecoater(WS-400B-NPP)spin-processor(LaurellTechnologiesCorp)dynamicinterfacialtensionanalysis,theimportantunder-at1500rpmfor20sundernitrogenenvironment,andthefilmswerestandingsofpolymerbehaviorattheinterfaceofdifferentoilsdriedintheovenat105°Covernight.Inthisexperiment,adropofareplausible.Hence,thesurfaceloading(Γ)wasevaluateddeionizedwater(DI)wasplacedontheSEKL-coatedglassslide,andusingGibbsadsorptionisotherms,asitwaspreviouslyusedforthecontactangleofSEKLatthewater−airinterface(WCA)waslinkingsurface/interfacialtensionofthesystemtothesurfacedeterminedfollowingstaticcontactanglemeasurementwiththe26−28sessiledropmethodat25°C.35Then,theglassslidewiththewaterconcentrationofpolymers.Inaddition,themodifiedWardandTordaidiffusionmodelwasimplementedforthedropletonitssurfacewasintroducedtoachamberfilledwithpurifiedearlystagesofadsorption29−31toassessthediffusionbehaviororganicphase(i.e.,xylene,cyclohexane,ordecane)toreflectthesituation,inwhichemulsificationoccurswhenSEKLpolymersareofSEKLfromthebulksystem(i.e.,water)totheinterfaceand24dispersedinwaterfirstandtheninteractedwithoilinterface.AftertofurtheridentifythemechanismofSEKLadsorptionat32theoil−waterphasereacheditsequilibrium(1h),theOCAwasdifferentoilinterfaces.measuredaccordingly.ThesameprocedureswerefollowedinInseveralstudies,saltadditionwasfoundtofacilitatethedifferentsalinitiesatnewlypreparedcoatedglassslides.Theaqueousadsorptionofpolymersattheoilinterfacebyscreeningdropletsof10and100mMKClwereplacedontheSEKLcoatedpolymer−oilandpolymer−polymerelectrostaticrepulsionandslides,andtheWCAandOCAwereobtainedfollowingthesame33,34stepsexplainedabove.Allthemeasurementswererepeatedthreethusfacilitatingthestabilityofemulsions.Forinstance,thesolubilityandhydrophilicityofcarboxymethylatedlignin,times,andtheaveragecontactanglewasreportedineachexperiment.CML,wasreportedtodecreasewithincreasingthesalt2.5.DynamicInterfacialTensionMeasurement.Dynamicconcentration,whichimprovedtheinteractionofCMLwithinterfacialtension(γ)betweenSEKLofdifferentconcentrationsand10theorganicphasewasmeasuredusinganAttensionThetaBiolintheoilphase.Similarly,theroleofelectrostaticinteractionin36opticaltensiometerfollowingthependantdropmethod.Precisely,3theadsorptionofSEKLattheoil−waterinterfacewasmLoforganicsolvent(i.e.,xylene,cyclohexane,decane)waschargedevaluatedinthisstudy.toaQuartzcuvetteandsealedtominimizethevolumeloss.InonesetLastly,tofindoutwhetherthereisacorrelationbetweentheofexperiments,theSEKLconcentrationwasvariedfrom0.25to1.5interfacialpropertiesandemulsionstability,emulsionstabilitywt%at0mMKClionicstrength.Then,5μLdropletsofSEKLwasevaluatedusingconfocalmicroscopyandacceleratingsolutionsatvariableconcentrationsweregeneratedatthetipofa36centrifugaldestabilizationinstruments.needle,whichwassubmergedintotheoilphase.Theimagesofthedropletswererecordedover3600sataframerateof10imagespersecondinthefirst600sand1imageperminuteinthelast3000s.2.EXPERIMENTALSECTIONTheinterfacialtensionswerecalculatedfromtheanalysisoftheshape372.1.Materials.Softwoodkraftlignin(KL),whichwasproducedofdropletsusingtheYoung−Laplaceequation.Inallcalculations,densityvalues(at22°C)wereconsidered997kg/m3forwater,864viatheLignoForcetechnology,wasreceivedfromFPInnovations.kg/m3forxylene,730kg/m3fordecane,and779kg/m3forAlso,2-bromoethanesulfonatesalt(NaBES98%),sodiumhydroxide38(NaOH,97%),potassiumchloride(KCl),sodiumnitrate(NaNO3),cyclohexane.Thesteady-stateinterfacialtensions(γ∞)foralloil−sulfuricacid(H2SO4,98%),hydrochloricacid(HCl,37%),dimethylwatersystemsstudiedinthisworkwereobtainedfromtheinterceptssulfoxide-d6(DMSO-d6),cyclohexane(C6H12),deuteriumoxideofplotsofγagainst1/√t.Areferencebaselinefortheγoftheoil−(D2O),poly(ethyleneoxide)s,andcellulosemembrane(1000g/watersystemswasinitiallyestablished(FigureS1).Thevalueofγ∞ofmolcutoff)werepurchasedfromSigma-Aldrich.Xylenexylene,cyclohexane,anddecaneagainstpurewater(i.e.,oil−water(C6H6(CH3)2≥98.5%,ACSgradeasamixtureofortho,meta,interfacetension)wasfoundtobe35,44,and47mN/m,respectively,andparaisomers,n-decane(C10H22),andNilereddyewereandthevalueswereconstantduringthemeasurements.Theseresults11,39,40purchasedfromFisherScientific.Allchemicalswereusedwithoutarecomparablewithreportedvaluesinotherliterature.Infurtherpurification.anothersetofexperiments,theconcentrationofSEKLwas2.2.SynthesisofSulfethylatedKraftLignin.DriedKLpowdermaintainedconstantat0.8wt%inthepresenceof10and100wasusedasaprecursortosynthesizeSEKLfollowingourpreviouslymMKClconcentrations.Then,theaboveanalysiswasrepeatedto12establishedmethod.Thealkalizationofhydroxygroupsoflignin(adetermineinterfacialtensionsinsalinesystems.Repeatedmeasure-20g/Laqueoussystem)wascarriedoutinthepresenceofsodiummentsofthesameexperimentwerewithin±0.5mN/m.hydroxidetoformionizednucleophiles.ThephenolionsthenreactedInadditiontointerfacialobservations,thecriticalaggregationwith2-bromoethanesulfonatesalt(NaBES)undertheconditionsofconcentration(CAC)pointofSEKLwasdeterminedtoshapeat0.82/1mol/mol(NaBES/KL),80°C,and4hreactiontimeinathree-wt%concentration,andfurtherdetailsofsurfacetensionanalysisareneckglassflasktoproduceSEKL.Uponcompletionofthereaction,providedintheSupportingInformation(FigureS2).thereactionmediumwascooledtoroomtemperatureandthen2.6.EmulsionPreparation.Differentemulsionsystemswereneutralizedwith5wt%H2SO4.Afterward,itwasdialyzedusingapreparedinthisstudyusingxylene,cyclohexane,anddecaneasthecellulosemembranefor4daystopurifytheproductsfromsaltsandorganicoilphasewithvariedchemicalstructures(FigureS3).unreactedreagents(i.e.,Na+,SO2−)whilechangingthewatereveryDifferentstocksolutionsofSEKLat0.25,0.5,0.8,and1.5wt%43347https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

2Langmuirpubs.acs.org/LangmuirArticleconcentrationsinthesalt-freesystemandat0.8wt%SEKLin10andof10±1kg/moland1.80forSEKLcomparedto6.5±0.5100mMKClsystemswereprepared.Theemulsionswerepreparedand2.1kg/molforKL,andtitrationexperiments(detailbymixingSEKLstocksolutionsanddifferentoilsinthevolumetricavailableinSupportingInformation)showedthesulfonateratioof1/1usinganultrasonicinstrument(Omni-Ruptor4000,groupcontentof1.2and0mequiv/gforSEKLandKL,OmniInternationalInt.)at240Wpowerand3sintervalfor30sandrespectively(TableS1),whichconfirmedthesuccessoftheroomtemperature.sulfethylationreaction.2.7.MicroscopicStructure.ThemicrostructureofpreparedemulsionswasobservedbyaLeicaTCC-SP8confocallaserscanning3.2.StabilityofSEKLSolution.Aswasshownpreviously,microscope(LeicaMicrosystemsInc.,Germany)equippedwithaSEKLformsastablesolutionatpH7inasalt-freesystemwith12WLLlaser(563nmexcitationwavelengths)usinganHCPLAPOCS2noobservableagglomerationorprecipitationovertime.The100×/1.40oilimmersionobjectivelens.Inthissetofexperiments,effectofionicstrengthonthestabilityofSEKLsolutionswas200μLofallpreparedemulsionswithoutdilutionweretakenfromevaluatedbymonitoringthechangesinelectrostaticpotentialtheemulsionlayerofthesamplesandstainedusingthe5μLofNile(ζ)andhydrodynamicsize(Rh)ataconstantconcentration41reddyesuspensioninwater(0.05wt%).Thestainedsampleswere(FigureS6),andtheresultsaresummarizedinTable1.At0.8placedonaglassslidewithacoverglassslideonthetop.Redfluorescencewasobservedwitha600−710nmfilterundera563nmlaserillumination.Table1.PhysicochemicalPropertiesofSEKLSolutions2.8.EmulsionStability.TheacceleratedstabilityoftheSEKLconcentrationKClmeanRh(nm)ζ-potential(mV)emulsionsusingadispersionanalyzer(LUMiSizer611,LUM(wt%)(mM)(±2)(±3)GmbH,Berlin,Germany)wasmeasuredtodeterminethelong-time420.8021−45storagestabilityoftheemulsioninthisstudy.Thisinstrumentcan0.81035−31reflectthemovementofemulsiondropletsthroughthesample.Undilutedemulsionswerepreparedasexplainedintheprevious0.810043−20section,andtheywereplacedinseparatecellsandsubjectedtoacentrifugalforceofthisinstrument.Uponthecentrifugation,theheavierandlighterphasesstartedtoseparate,andmigrationhappenedwt%SEKL,thechargescreeningdroppedthemagnitudeofζthroughthecell,whichcausedlighttransmissionthroughthecells.fromaninitialvalueof−45±3mVintheabsenceofsalttoSimultaneously,near-infraredlightoftheinstrument(λ=865nm)−31±2and−20±2mVatelevatedsalinity,suggestingthatwasappliedtoilluminatethesamplestodeterminetheinstabilitysaltscreenedsomeofthesurfacechargesofthepolymer42indicesbytheincludedsoftware(SepView6.0;LUM).The(Table1).Thesamebehaviorwaspreviouslyreportedforthedimensionlessindexwasquantifiedbytheclarificationatagivengraftedligninpolyacrylamide,astheζofitssolutiondropped43separationtimedividedbythemaximumclarification.Thedramaticfrom−40to−22±2mVwhentheNaClconcentrationseparationofphasesisanindicationoftheinstabilityofemulsions,13increasedto10mM.whichresultsinalargerinstabilityindex.Theintegrationgraphswerealsogeneratedanddescribedasthe“creamingrate”,whichshowedThemeanRhofSEKLwasincreasedinhighersalinitythetransmittedlightinpercentovertime.Thehighercreamingrate(Table1),whichsuggeststheaggregationofpolymersatrepresentsthelowerstabilityofemulsionsandviceversa.Thehigherionicstrengths.Ligninisknowntodevelophydro-operationalparametersofthetestswerethetotalsamplevolumeofphobicinteractions,suchasvanderWaalsandπ-stacking0.4mLofemulsion,thewavelengthof865nm,therotationalspeedofforces,whichstronglycontributetothenanoaggregationof112G,experimentaltimeof1000s,theintervaltime(betweenpolymersleadingtoahigherhydrodynamicsizebyscreeningrecording)of1s,andthetemperatureof25°C.theelectrostaticrepulsionbetweenthem.44,45Theseresults2.9.ZetaPotential.Theζ-potentialofallsolutionswasalsoagreewiththeDLVOtheory,46,47whichpredictstheanalyzedusingaZetaPALSanalyzer(BrookhavenInstrumentsCorp,accumulationofpolymersbyadecreaseinthedoublelayerUnitedStates).Eachsamplewasmeasuredthreetimes,andtherepulsionthroughsaltscreeningthatcausedaggregationtoaaveragevalueswerereported.certainlevel.However,theSEKLsolutionwasstillstablewithTheζ-potentialoftheemulsionwasmeasuredusingthesameinstrument.Emulsionsampleswerepreparedfollowingthemethod-noobservableprecipitation(FigureS7)duetothesufficient48ologystatedinSection2.6,andtheywerediluted100timesinelectrostaticrepulsion(ζ<−20mv).However,clusterswithdeionizedwater.ThesampleswereloadedintothecellsandanalyzedlargerRhwereformedatelevatedionicstrength.atthelaserwavelengthof659nmandthescatteringangleof90°.Zeta3.3.InterfacialAnalysis.3.3.1.WettabilityandCompat-potentialmeasurementwascarriedoutasafunctionofSEKLibilityofSEKLatOilInterfaces.ThecontactanglesofSEKLconcentrationandoiltype.AtleastthreemeasurementswerepolymersattheWCAandOCAinterfacesweremeasured,andperformedforeachsample.theresultsareshowninFigureS8.WCAat0mM(36.6°)2.10.StatisticalAnalysis.AllmeasurementswereimplementedrepresentsthehydrophilicnatureofSEKL,whichisassociatedintriplicate,andtheresultswerereportedasmeanandstandardwiththefunctionalgroups,suchassulfonatemoieties,deviations.AnalyseswerecarriedoutinExcel2016forWindows(MicrosoftOfficeHomeandStudent,2016).anchoredonlignin.ThepartialneutralizationofthesurfacechargesofSEKLbycounterions(i.e.,K+)compressedthedoublelayer,weakenedelectrostaticrepulsiveforces,andthus3.RESULTSANDDISCUSSIONreducedtheζ-potential(Table1),whichprobablyexposedthe3.1.SEKLFormulationandCharacterization.InthishydrophobicfeaturesofSEKLandthustheSEKLcoated49,50study,2-bromoethansulfonate(NaBES)wasusedtoproducesurface.Theincreasedsalinityresultedinanupsurgein22SEKL.Briefly,thereactionfollowedanucleophilicWCA(39°and43°at10and100mMKCl,FigureS8)andsubstitutionmechanism(SN2)wherealkoxyionsfromtheelevatedthehydrophobicityofSEKLcoatedsurfaceinsalinedissociationoflignin’shydroxygroupsinanalkalinemediumsystems.substitutedwithbromineionontheNaBESsalt(FigureS4).TheOCAisshowntobedependentontheoilsystem,The1Hand2H−HNMRspectraoftheproductsandrawwhichisthelowest(∼25°)atthexyleneinterfaceandgreatermaterialconfirmedthegraftingoftheethylgroupontheligninatcyclohexane(∼27°)anddecane(∼36°)interfaces.Thestructure(FigureS5).TheGPCrevealedtheMwandMw/MnlowestOCAatthexyleneinterface(FiguresS8)impliesthe3348https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

3Langmuirpubs.acs.org/LangmuirArticle55leastfavorableinteractionbetweenSEKLandxyleneinterface,Bergfreundetal.ontheadsorptionofnanocrystals(CNCs)despitethemutualstructuralaromaticity,whichshouldbeatdifferentoilinterface.relatedtothehigherpolarityofxyleneattheinterface(2.5,ImplementingtheGibbsadsorptionequation(eq1),the51TableS2).Ontheotherhand,thebettercompatibilityofsurfaceloadingofSEKLpolymersperunitareaattheinterface56SEKLwithcyclohexaneanddecaneinterfaces(i.e.,largerwasidentified.OCA°)withaliphaticstructuresshouldbeassociatedwiththeelevatedhydrophobicinteractionsattheinterfaceduetothe1dγ∞Γ=51nRTlncd(1)limitedoilpolarity.Inaddition,chargescreeningeffectivelyimprovedtheOCA2Inthisequation,Γstandsforsurfaceloading(mol/m),γ∞(to∼35°),whichwasindependentoftheoiltypeat10mMistheequilibriuminterfacialtensionobtainedfromFigureS10KCl(FigureS8)butoriginatedfromtheeliminationofandTable2,cistheSEKLconcentrationinthebulksolution,electrostaticrepulsionandenrichmentofhydrophobicnaccountsfortheionicstateofthepolymer(n=2forionicinteractions.At100mMKCl,theOCAatthexyleneinterfacepolymersandn=1fornonionicpolymers),Tistheabsolutewasraisedto53°,whileitwas42°and44°forcyclohexaneand13temperature,andRisthegasconstant.decaneinterfaces,respectively(FigureS8).ThesesuperiorTheareaoccupiedbySEKLattheinterface(a)canthenbehydrophobicinteractionsbetweenxyleneandSEKLstructurecalculatedfollowingeq2:probablyoriginatefromtheπ−πinteractionsassociatedwiththeirmutualaromaticstructure,whichisabsentincyclohexaneMwa=anddecanesystems.ΓNA(2)3.3.2.DynamicInterfacialAnalysis.Thedynamicinter-facialtension(γ)isafundamentalquantitythatisrelatedtowhereMwisthemolecularweightofSEKL(10kg/mol)and13theassemblypropertiesofadsorbedmaterialsatinterfacesandNAisAvogadro’snumber.ThecomputedΓandaforallplaysacrucialroleintheprocessofemulsionformationandsystemsareshowninFigures1aand1b.stabilization.52PolymericsurfactantsreduceγbymigratingtoTheresultsdisplayacontinuousincreaseintheinterfacialtheinterfacebeforetheirconcentrationreachesequilibriumatloading(Γ)whenmoreSEKLisavailableinthebulksystemtheinterface.53Inthisstudy,thedynamicγwasmeasuredvia(Figure1a).ThenumberofSEKLpolymersattheinterfacereachedthemaximumamountof7.3×10−4,9.2×10−4,andpendantdroptensiometryanddrop-shapeanalysisforallsystemsatdifferentSEKLconcentrationsover3600s,andtheresultsarepresentedinFigureS9.Thesteady-stateinterfacialtensions(γ∞)foralloil−watersystemswereobtainedfromtheinterceptsofplotsofγagainst1/√t(FigureS10)fromdataoft>1900sinFigureS9,whereaminimalalterationinγisobserved,andtheresultsaresummarizedinTable2.Table2.Steady-StateInterfacialTensions(γ∞)forAqueousSolutionsofSEKLatXylene,Cyclohexane,andDecaneInterfacesinSalt-FreeSystemsSEKLγ∞(mN/m)γ∞(mN/m)(±0.5)γ∞(mN/m)(wt%)(±0.5)xylenecyclohexane(±0.5)decane03544470.2512.117.316.50.511.914.615.50.811.013.715.01.510.712.214.1Asexpected,thechangesinγforallsystemsattheoil−waterinterfacesdependontheconcentrationofSEKLintheaqueoussolutions(FigureS9),asthehigherdosagesofSEKLinthebulksystem(e.g.,1.5wt%SEKL)yieldedlowerfinalγvalues(γ∞inTable2).Also,therateofdeclineinγvariedovertime,whilechangesweresteeperinthefirst250softhetest,anditreachedaplateauatthelaterstageofanalysis,suggesting21,54thatthepolymerassemblyreachedanequilibrium.Basedonγ∞andγ0(pristineinterfacialtension)atdifferentoilinterfaces(Table2),thehighersurfacepressure(Δγ=γ∞−γ0)wasdeterminedforthedecaneinterface(33mN/m)thanforcyclohexane(31.8mN/m)andxylene(24.3mN/m)atthehighestSEKLconcentration,whichimpliesahighersurfaceactivityofSEKLatthedecaneinterface.ItisimpliedFigure1.(a)Computed(Γ)and(b)computed(area,a)forSEKLasthatthehigherpolarityoftheoilattheinterfacewasassociatedafunctionofbulkconcentration(wt%)atxylene,cyclohexane,andwithlesssurfacepressurevariationsaswasalsoreportedbydecaneinterfaces.3349https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

4Langmuirpubs.acs.org/LangmuirArticleFigure2.plotsofγvstshowingdifferentstagesofinterfacialdepletionatdifferentoilsystemswithincreasingSEKLwt%andionicstrengths.9.6×10−4mol/m2forxylene,cyclohexane,anddecaneastheadsorptionofSEKLincreasedattheinterface,theareasystems,respectively.Thetrendforinterfacialloading(Γ)ofofoccupationofSEKLdecreasedaccordingly.ResultsinSEKLattheoilinterfacefollowsthetrendinthesurfaceFigure1bdepictedthesmallestsurfaceoccupation(a)forthepressureattheseinterfaces(Table2),whichrevealsthehigherSEKLattheinterfaceofdecane(17.2−23.6nm2)andtheinterfacialactivityofSEKLatthedecaneinterface.Moreover,largestattheinterfaceofxylene(22.7−32.3nm2).Therefore,it3350https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

5Langmuirpubs.acs.org/LangmuirArticlecanbeconcludedthattheoiltypeplaysavitalroleintheFigure2fortheearlystagesofadsorption.WhilethechangesinterfacialactivityofSEKLattheinterface.ofγinthefirststagearesmall(t→0),alargerslopeofγvstVarioussurface-sensitivetechniques,suchasneutronwasobservedforthesecondstage(t→t1).Thetransition57reflectometry(NR),vibrationalsum-frequencygenerationbetweentwostageshappenssoonerforSEKLatdecane5839spectroscopy(SFG),orellipsometrywerepreviouslyinterfacethanatcyclohexaneandxyleneinterfaces.Accord-implementedtoexperimentallymeasurethesurfaceloadingingly,D*t→0andD*t→t1areobtainedfrom(eq4)usingtheorareaofoccupationofmoleculesatair−wateroroil−waterslopeofaplotofγvstfromFigure2forbothstages(slopesinterfaces.Thesemethodsreportedresultsthatwerealigned67areshowninFigureS11).withthetheoreticalGibbsadsorptionforanalyzingsurfaceorinterfacialtensionforawiderangeofsurfactantsandTheD*t→0andD*t→t1ofSEKLatdifferentoilinterfacesarepolymers.59Inanotherstudy,60thesurfaceloading(Γ)ofdepictedinFigure3a,bandiscomparedwiththebulkdiffusionD(2×10−12m2/s)tofindouttheadsorptionpolyethyleneglycolatedligninpolymersattheair−waterinterfacewasmeasuredviaellipsometry,andtheexperimentalmechanism,whichisnotsimilarinallsituationsandwillberesultswerecorrelatedtothesurfacetensiondeterminedfurtherdiscussedhere.followingtheGibbsadsorptionequation.Also,adeviationeq5wasappliedtoquantifythedifferencesbetweenDand68betweentheoreticalandexperimentalresultswouldbeD*,whereΔEp→0/t1,i.e.,theactivationenergyofattachedpossible,whichwoulddependontheaccuracyoftheSEKLattheinterface,determinestheextenttowhichtheoreticalmodelsusedandthenatureofsurfactants(i.e.,adsorptioniskineticallylimited(notdiffusion-controlled).64,6961cationicoranionic).3.3.3.DiffusionintoOilInterface.ThethreemaintypesofijjΔEp→0/tyzzadsorptionkineticsforpolymersatinterfaceshavebeenDD∗=−expjj1zztt→0/1jjzzreportedtobediffusion-controlled,energy-barriercontrolled,jkTBz(5)k{62oramixedbarrier-diffusion.Itisgenerallyacceptedthattheadsorptionprocessatthepristineinterfaceisdiffusion-Thisequationcanexplainthesituationinwhichthediffusion62controlledwhenthereisnoenergybarrier.Inthiscase,ofamoleculeandsubsequentlyitsadsorptionattheinterfaceispolymermoleculeseasilymigratefromthebulktothepristinehamperedforsomereason,e.g.,stericorelectrostaticinterfaceandfreelyadsorb.Forabetterunderstandingoftherepulsionsaswellasrestructuringinthecaseofbulky70,71adsorptionprocess,theanalysisoftheeffectivediffusivity(D*)macromoleculessuchaspolymersandproteins.Consid-ofSEKLintotheoilinterfaceisimportant.FindingeffectiveeringtheresultsofD*t→0andDinFigure3a,theapparentD*tobemuchsmallerthantheestimateddiffusioninthebulkinconsistenciesexistforbulkDdependingontheoiltypeandphaseindicatestheexistenceofanadsorptionbarrier,whilepolymerconcentrations,andΔEp→0calculationsidentifythis63similarvaluesshowdiffusion-controlledadsorption.Inthedifferenceasanenergybarrieruponadsorption(Figure3c).presentwork,theestimateddiffusioncoefficientofSEKLinInthecaseofthedecanesystem,theD*t→0wasgreaterthanbulkwaterwasanticipatedtobe2×10−12m2/susingthethebulkD,whichrevealsthediffusion-controlledadsorptionin64Stokes−Einsteinequation(eq3):theearlystageofadsorption(stage1)becausethediffusion-controlledadsorptionmodelofWardandTordaiassumesthatKTD=thetransferfromthesubsurfacetotheinterfaceisfaster6ΠμRh(3)comparedtothetransportfromthebulktothesubsurface.62wherekistheBoltzmannconstant,Ttheabsolutetemper-Therefore,weobtainedΔEp→0≈0kBT(i.e.,theorderofthermalfluctuations)forallSEKLconcentrations,indicatingature,μistheviscosityofthesolution,andRhisthehydrodynamicradiusofSEKL.64thevalidityofeq4anddiffusion-controlledadsorptioninstage62,72ThemodifiedWardandTordaidiffusionmodel31was1atthedecaneinterface.Inthecaseofthecyclohexaneinterface,thisvalidationisimplementedtoexpressthediffusionphenomenonofSEKLonlyapprovedintheconcentrationrangeof0.25−0.5wt%;fromthebulksystem(i.e.,water)totheinterface.Assumingtheadsorptionbarrierisnotsignificantatthepristineinterface,whileat0.8and1.5wt%SEKLconcentrations,theD*t→0decreasedto2.22×10−14and6.65×10−15m2/s,whichwas2eq4canbeappliedaspreviouslyusedforpolymersand−122proteins.64−66Inthiscase,theadsorptionprocessisto3ordersofmagnitudesmallerthanbulkD(22×10m/characterizedbyD*t→0,effectivediffusioncoefficientsinas)(Figure3a),resultingintheΔEp→0of4.5and5.7kBT,respectively.Therefore,theadsorptionkineticsofSEKLattheshorttime(t→0),inwhichasingleSEKLpolymeriswater-cyclohexaneinterfaceisonlydiffusion-controlledbelowadsorbedontoafreeinterface:itsCACpoint(0.8wt%),abovewhichanenergybarrierexistsD*t→0(duetoΔEp→0≥0kBT).Atthexyleneinterface,variationsγ=−γ02nRTC0×tbetweenD*t→0andbulkDisapplicableatallSEKLwt%π(4)ranges,whichresultsinΔEp→0=1.6−7kBT,suggestingthatanHere,γandγ0arethedynamicinterfacialtensionsattimetandenergybarriertotheadsorptionexistsandadsorptionisno72pristineinterface,respectively,nis1fornonionicpolymersandlongerdiffusion-controlled.2forionicones.C0istheSEKLconcentrationinthesolutionInthesecondstageofadsorption,differentbehavioris(i.e.,water),Tisthetemperature,andRistheuniversalgasobserved,andthediscrepancyisonlyvisibleatconcentrationsconstant(8.314J/mol.K).beyondCACpoint(1.5wt%)foralloilsystems(Figure3b).Thechangesinγvstintheinitialtime(ts=15)isAsaresult,ΔEp→t1=0forstage2(Figure3d)isassociatedshowninFigure2,wherethesharpestdeclineinγwaswithdiffusion-controlledadsorptionforalloilinterfaces.observed(FigureS9).Remarkably,wedetectedtwoSEKLconsistsofhydrophilicsegmentsofsulfonateanddistinguishablestraightlinesofγagainsttasshowninhydroxygroupsandhydrophobicaromaticandaliphatic3351https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

6Langmuirpubs.acs.org/LangmuirArticle56cores.ThefirststepofSEKLadsorptionwasfoundtobekineticallylimitedatcyclohexaneandxyleneinterfaces(Figure3c)duetotheexistingenergybarrier,whileitwasbarrier-free(ΔEp=0)atthedecaneinterface.Ionicmolecules,e.g.,SEKL,areunabletoeasilydiffuseintotheinterfaceduetotheirstrong73hydrogenbondsformedwithwatermolecules.Ontheotherhand,thenetinteractionsbetweenSEKLandtheoilsurfacemayincludenotonlyvanderWaalsandhydrophobicattractionbutalsoelectrostaticrepulsionduetotheionic30characteristicsofSEKL(ζof−45mV).Hence,itissuggestedthatthesuperiorhydrophobicinteractionsofSEKLwithdecaneshouldhaveresultedinbarrier-freeadsorptionbyexceedingthehydrogenbondingandelectrostaticrepulsion,whilethehydrophobicinteractionsatcyclohexaneandxylenewerelesssignificant(OCAresultsinFigureS8).AsisschematicallyillustratedinFigure4,whenSEKLarrivesattheFigure4.SchematicillustrationofSEKLadsorptioninstage1andstage2atcyclohexaneandxyleneinterfaceinasalt-freesystem.hydrophobicinterfaceofoil,thehydrophobicsegmentofSEKLinitiallyinteractswiththeoilinterfaceandrestructuresbyfacingitshydrophilicmoietiesoutwardthewaterphaseandthehydrophobicsegmentstowardtheoilphase,whichis14,72analogoustoproteindenaturationatanoilinterface.Thiscanbeascribedtothe“unfolding”ofSEKLatthewater−oilinterface,astheinteractionsswitchfromSEKL−waterinthe25,63bulktoSEKL−oilattheinterface.ThisstepofrestructuringofSEKLatoilinterfaceswasshowntobediffusion-controlled(Figure3d).Theelimination(orreduc-tion)ofhydrogenbondingandeffectiverestructuringofSEKLatoilinterfacesshouldhavefurtherassociatedwithstrongerhydrophobicinteractionsandlesselectrostaticrepulsionbetweenSEKL−oilinterfaces;therefore,theenergybarriernolongerexists.Instage2,twoprocesseswouldoccursimultaneously:(1)thediffusionprocessofapproachingmoleculesfrombulksolution,whichmakestheadsorbedlayerdenserthatcausesthecontinuousdepletionoftheinterfacialtension;and(2)thereorientationofSEKLsegmentswithintheadsorptionlayer,leadingtoadiffusioncontrol74,75process,aswasreportedinthepast.TheobservableΔEpbeyondtheCACpoint(at1.5wt%)Figure3.(a)DiffusioncoefficientsD*t→0(eq4)instage1,(b)D*t→t1couldbeassociatedwiththechangesintheconformationor63,76(eq4)instage2,(c)energybarrierΔEpt→0(eq5)instage1,and(d)nanoaggregationofactivesolutes,i.e.,macromolecules.ΔEpt→t1(eq5)instage2oftheSEKLofdifferentconcentrationsCACisstatedtohaveasignificanteffectinthediffusivityof(0.25−1.5wt%)atdifferentoilinterfaces.macromoleculesthatcausedanabruptchangeinD*t→t13352https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

7Langmuirpubs.acs.org/LangmuirArticleTable3.EffectofKClConcentrationontheKineticParametersofSEKLAdsorptionatEarlyStagesofAdsorptionatDifferentOilInterfacesand0.8wt%SEKLConcentrationstage1stage2oilphaseKCl(mM)D*(eq4)(m2/s)ΔE(eq5)(KT)±0.5D*(eq4)(m2/s)ΔE(eq5)(KT)±0.5t→0p→0Bt→t1p→t1Bxylene01.95×10−132.31.87×10−120.06101.01×10−120.39.30×10−130.401002.58×10−1202.58×10−130.63cyclohexane0220×10−144.51.36×10−120.40107.83×10−130.61.90×10−120.201002.86×10−1205.80×10−130.60decane01.78×10−1104.30×10−120.00102.10×10−1205.80×10−130.801003.64×10−131.15.25×10−130.70Figure5.Confocalimagesoftheemulsionspreparedfromxylene,cyclohexane,anddecaneastheoilphaseandSEKLaqueoussolutionsatconcentrationrangesof0.25−1.5wt%andinsalinesystems(10and100mM).Thescalebaris5μminallimages.63(Figure3b),whichfurtherrestrictedtherestructuringofSEKLadsorptionisvalid.TheincrementinD*t→0andreductionin63attheinterface.energybarrierathighersalinitywaspreviouslyreportedtoUltimately,itcouldbesummarizedthatSEKLshowedaassociatewiththereducedpolymer−interfacerepulsion.32betterinterfacialactivityatthedecaneinterfaceintheinitialSimilarly,electrostaticrepulsionamongSEKLpolymerswasstageofadsorption;however,suchactivitywasimprovedlatershowntobeweakenedatelevatedsalinesystemsbasedonζ-atxyleneandcyclohexaneinterfacesinthesecondstage,inpotential(Table1),andstrongerhydrophobicinteractionswhichdiffusion-controlledadsorptionwasdevelopedatalloilwereformedattheoilinterface(OCAresultsinFigureS8),interfaces.whichresultedineffectiveadsorptionatxyleneandcyclo-3.3.4.DiffusionandAdsorptionMechanismsinSaltyhexaneinterfacesinthepresenceofSEKL.Systems.ThechangesinD*t→0andD*t→t1(calculatedInterestingly,areverseshiftwasobservedatthedecaneaccordingtoeq4andtheslopesinFigureS11)andinterfacecomparedtoxyleneandcyclohexaneinterfacesforcorrespondingΔEp→0andΔEp→t1(eq5)attheearlystagesSEKLadsorptioninthefirststage,andD*decreasedat100t→0ofadsorptioninacceleratedsalinitysystemsarealsomMsalinity,resultinginΔEp=1.1KBT.AshydrophobicsummarizedinTable3.interactionswerealreadydominantinthecaseofSEKLAninterestingobservationinstage1wastheincrementinadsorptionatthedecaneinterfacewithdiffusion-controlledD*t→0by1−2ordersofmagnitudeattheelevatedsalinityadsorptioninthefirststageofthesalt-freesystem,chargecomparedtothesalt-freesystemforcyclohexaneandxyleneinterfaces,whichmadeΔEp→0=0kBTat100mM.Itindicateseliminationdidnotacceleratethediffusion(Table3).Onthethatthesaltconcentration(100mM)wassufficienttootherhand,thebulkierclustersofSEKLhadslowerdiffusioneliminatetheadsorptionbarrierbecausethediffusivitiesintotheinterfaceduetoSEKL’sagglomeration(Table1).calculatedfromWardandTordaiwouldrecoverthebulkTherefore,abarrierisdevelopedagainstadsorptionat100mMvaluesmeasuredwithDLS,andthus,diffusion-controlledsaltconcentration.3353https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

8Langmuirpubs.acs.org/LangmuirArticleaTable4.ComparisonofSEKLasanEmulsifierwithPreviouslyReportedPolymericSurfactantsemulsionsystem/oiloildropletinstabilityindex/contactequilibriuminterfacialemulsifier,dosagecontent(wt%)size(μm)instrumentangleθtensions(mN/m)D(m2/s)refH2OSEKL,0.25−1.5%xylene,cyclohexane,15to20.8to0.04(Lumisizer)36°10.7,12.2,14.11.87×10−12,thisdecane,50%1.36×10−12,study4.3×10−12OSA-starches,MCT,5%0.2−0.25ΔT%=10−30%38.1−246.9×10−7to4.7×10−6830.125−1wt%(Turbiscan)pectin,1%rapeseedoil,30%25−102×10−12to1.2×10−1186LPI,0.1−30oliveoil,10%12to0.4ESI=24−386h121.22×10−1366mg/mLgravitationalsettlingLG,0.5wt%sunfloweroil,10%1.739TSI,930.50°588LA1.777849.33°WPI15(Turbiscan)KL-TA,1.5%cyclohexane,50%6−12TSI20(Turbiscan)20°21.711CMLs,2%kerosene,30−70%1.7−3surfacetension65−6210OSA-CFG,0.5−soybean,5.0%1.5−2.50.75to0.2533to25interfacialviscoelasticity191.5%(Lumisizer)studiesaΔT:transmissiondifference.ESI:emulsifyingstabilityindex.Instage2,D*t→t1isdecreasedinoppositiontostage1,andshowedthatformulatedemulsionwithdecaneastheoilphasewasmorestablecomparedtotheothertwooils,andtheΔEp→t1increasedtolessthan1kBT.Inthesaltysystem,thestabilityforallsystemswasimprovedbyconcentratingthebulkalreadyadsorbedclustersarebulkierandthereforemoresolution(instabilityindexdecreased).Moreover,theinstabilitydifficulttorestructureattheinterface.Therefore,astericindexreductionwaslimitedto0.36and0.25inthecaseofbarrierexistedfortherestructuringofadsorbedSEKLandthexyleneandcyclohexanesystems,respectively,whileitreachedadsorptionofnewpolymersfromthebulk,whichresultedin0.04forthedecaneemulsion.ΔEp>0KBTinstage2.Instabilityindexdepletionwithincreasingthebulk3.4.EmulsionsObservation.Physicalobservationandconcentrationisentirelyconsistentwiththevariationsinthestabilityofemulsionwereanalyzedthroughmicroscopicdropletsize(Figure5),whichfollowsStoke’slawstatingtheimagingandphysicalstabilityanalysisundercentrifugalforces.smallertheoildropletsize,thelowerthecreamingrateofTheemulsionphaserestedatoptheexcessaqueousphase,80,81emulsions.Thecreamingrateofemulsionsalsodecreasedsuggestingthatthesystemwasanoil-in-water(O/W)50withincreasingbulkconcentration,whichisevidentfromtheemulsion,whichwasanticipatedfromcontactanglesmallerslopesoftransmittancewithpositionandtheintegralmeasurements(θ<90°)(FigureS8).82transmissionasafunctionoftimeinFigureS13aandb,3.4.1.ConfocalImages.Theconfocalimagesoftherespectively(showedonlyforthedecanesystem).Allζ-valuesemulsionsformulatedfromdifferentoilsarepresentedinwerenegativeatthelowestSEKLdosage(decane−36±2Figures5.TheoilphaseisdemonstratedbygreencoloraswasmV,cyclohexane−35±3mV,andxylene−36±2mV)duestainedbythedye.Thevariationsintheoildropletsizeare83tothepresenceofsulfonateanionicgroupsonSEKL.Theobservablebychangingtheoiltypeandbulkconcentration.Itisinferredthatxylene,astheoilphase,contributedtothemagnitudeofζ-potentialofemulsionsincreasedforallthree83formationofthelargestoildroplets(∼15μm),whiledecaneoilsbyconcentratingtheSEKLbulksolution.Moreover,showedthesmallestdropletsize(<7μm)at0.25wt%SEKLdecaneexhibitedthehighestpotentialata1.5%SEKLdosageconcentration.Thefindingsfollowpreviousobservations(−55±3mV)comparedtocyclohexane(−50±2mV)andreportedontheformulationoflargeroildropletsforpolarxylene(−47±2mV),whichagreedwiththehigheststabilityoilscomparedtononpolaroils.77Also,apossibleexplanationofdecaneemulsionsinasalt-freesystem.Theseobservationsmightbethehigherinterfacialloadingatthedecaneinterface,werecoherentwiththeadsorptionresultsshowninFigure1a,whichfacilitatedtheproductionofsmalldroplets,aswasreflectingthatahigherΓatthedecaneinterfaceledtohigherreportedpreviously.78stabilitythatwasassociatedwithmorepackingandastrongerByfurtherincreasingthebulkconcentration,thesizeofoilbarrieratthedecaneinterface.Thefactthatthereductionindropletsdroppedinallformulatedemulsions(xylene∼7μm,theζofemulsionswascorrelatedtothesuperiorstabilityandcyclohexane∼5μm,anddecane≤2.5μmat1.5wt%).InasmallestdropletsizerevealedthatelectrostaticrepulsiveforcelowerSEKLconcentration,thenumberofpolymersadsorbedamongoildropletswasthemainmechanismofdroplet84attheinterfacewasnotsufficient;therefore,coalescenceorstabilizationinasalt-freesystem.flocculationwouldbeprobable,whichwouldresultinlargeroilAsubstantialreductionintheinstabilityindicesforalldroplets.79Inaddition,increasingthesalinityofthesystememulsionsathighersalinitywasobtainedastheoildropletsizedroppedtheoildropletsizetolessthan2.5μmforallsystemswassignificantlyreduced(Figure5).Theinstabilityindexwithoutfurthercoalescenceorflocculation.Chargescreeningreached0.01,0.01,and0.04forxylene,decane,andclearlycausesmorepackingofSEKLattheoil−waterinterface,cyclohexanesystemsat100mMsalt,respectively,suggestingwhichformedoildropletssmallerinsize.theultrastableemulsionformulationinthesalinesystems(the3.4.2.StabilityofEmulsions.ThestabilityoftheemulsionsimagesoftheemulsionsaftercentrifugingarepresentedinthewascomparedconsideringthechangesintheacceleratingSupportingInformationinFigureS14).Inthiscase,thephysicalinstabilityindex(FigureS12)andζ-potential(ζ)ofreducedelectrostaticrepulsionbetweenSEKLandtheemulsions.Thecomparisonofinstabilityindices(FigureS12)interface(duetothereducedchargeofpolymersinbulk3354https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

9Langmuirpubs.acs.org/LangmuirArticlesolution,Table1)andelevatedhydrophobicityofSEKLSEKLshowedbetteremulsionpropertiescomparedtotheformedastrongerintermolecularinteractionbetweenthepreviouslyreportedlignintannicacid(KL-TA)withahigherSEKL−oilinterfaceinthesalinesystem(WCAandOCAchargedensity(−2.8mmol/g)asastabilizer,whichformeda11resultsasshowninFigureS8),whichresultedinconcentrationlargeroildropletsizewithgreaterinstability.Itisknownthat12thehighersurfacechargesareassociatedwithlargeroilofSEKLatoilinterfaces.Itissuggestedthatthemain89mechanismofdropletstabilizationinthesaltysystemsisadropletsthatwillcauseinstabilityovertime.Carboxymethy-stericbarrierbasedonthebulkierpolymersandthereducedζ-latedlignin(CML)showedbetteremulsifyingpropertieswithpotentialofSEKLsolutionsathigherionicstrengths(Tableasmalleroildroplet;however,oneissuewithCMLisits85limitedaffinitytolowerthesurfacetension.10Inanotherstudy,1).Moreover,acorrelationisobservedbetweenthemagnitudehydrophobicallymodifiedcornfibergum(CFG)graftedwithofinstabilityindicesandtheresultsoftheOCAatdifferentoiloctenylsuccinateanhydride(OSA)wasreportedtoobtainsystems(FigureS8).Forinstance,thelargestandsmalleststabilizedemulsionsundercentrifugalforcesinthedosage19OCAatthedecaneandxyleneinterfaceswereassociatedwithrangeof1−1.5wt%,whichwascomparablewithSEKL’sthesmallest(moststable)andlargestoildroplets(leaststable)performance.Itshouldbestatedthat,comparedwiththeoil(Figures5andS12)inasalt-freesystem,respectively.Thefractionofthecurrentstudy(50%),theoilfractionwasmuchintenseincrementintheOCAinthesaltysystems(FigureS8)lowerinthestudiesdiscussedabove,whichcouldgreatlyaffectisalsoassociatedwiththehighlystableemulsionswiththetheemulsifyingcapacityofpolymers.smallestoildroplets(Figure5).Thismadetheemulsionstabilityindependentoftheoilchoice,astheemulsionswith5.CONCLUSIONSxyleneandcyclohexaneareasstableastheoneswithdecane.Forthefirsttime,asystematicanalysisoftheinterfacialbehaviorofapolymericligninsurfactant(SEKL)wasprovided4.COMPARISONtoidentifytheadsorptionperformanceofSEKLattheinterfaceofdifferentoil−watersystems.First,alteringtheComparingthephysicalpropertiesofemulsionsofdifferentpolarityandchemicalstructureoftheoilaffectedthesurfacesystemsischallengingastheoiltype,content,andpressureΔγ,surfaceloadingΓ,andcontactangleθofSEKLatemulsificationconditionscangreatlyaffectthemacroscopictheoilinterfaces,whichrevealedthehighestadsorptionpropertiesandultimatelythestabilityofthesystem.Theperformanceatthedecaneinterface.Theseobservationswerequantitativeanalysisfromthepreviouslyusedbio-basedassociatedwithstrongerhydrophobicinteractionsintheorderpolymersforstabilizingoil−watersystemsissummarizedinofdecane>cyclohexane>xyleneattheinterface.Second,theTable4.Asseen,severalstudieshavequantitativelyadsorptionbehaviorofSEKLwasnoticedtohappenintwocharacterizedthekineticsofadsorptionattheinterfacebydistinguishablestagesanalogoustodiffusionanddenaturation66,83,86calculatingdiffusivity.Forinstance,theDeffwasofproteinsattheoilinterface.Third,theimplicationofacalculatedforcitruspectinwithdifferentdegreesofmodifiedWardToradaidiffusionmodelforkineticadsorptionesterification,anddiffusion-controlledadsorptionkineticswasanalysisrevealedthatalthoughthediffusionwaskineticallyreportedat1wt%bulkconcentrationfortherapeseedoil−limitedintheveryfirstsecondsofadsorptionatinterfacesof86watersystem.Comparedwiththeresultsofthepresentoils(exceptfordecane),therestructuringinthesecondstagestudy,theoildropletsizewasmuchlarger,andincreasingsaltwasdiffusion-controlledforallsystems.Thechangesintheconcentrationfurtherenlargedthedropletsizeto50μm,interactionsfromSEKL−water(stage1)toSEKL−oil(stagewhichcauseddemulsificationduetostrongdropletcoales-2)eliminated(orreduced)thestronghydrogenbondingofcence.86Afairlysimilardiffusivityrate(1.22×10−13m2/s)towatermoleculeswithSEKLandassociatedwithstrongertheresultofthepresentstudywasreportedforlentilproteinhydrophobicinteractionuponrestructuringattheoil66isolates(LPI)attheoliveoilinterface.interfaces.Furthermore,chargescreeningathighersalinityThetwo-stagetransitionforSEKLadsorptionattheoileliminatedtheenergybarrierfortheSEKLadsorptionintheinterfacewasalsoidentifiedfortheamphiphilicderivativesoffirststageatxyleneandcyclohexaneinterfaces.Nonetheless,a8768chitinorchitosan,bovineserumalbumin(BSA)protein,newstericbarrierwasgeneratedinthesecondstage,which72andhydrophilicpolyethyleneglycol(PEG)NPs.Thesehinderedthediffusion-controlledreorientationofSEKLresultsshowedtobediffusion-controlledonthedynamicclustersatoilinterfaces.TheoveralladsorptionofSEKLatsurfaceandinterfacialanalysis.theinterfacewasdiffusion-controlled(consideringstage2asAnotherstudyusingAcrysolTT-935,apolymericsurfactant,thedeterminingstage)atalloilinterfacesinasalt-freesystem.andsoylipophilicproteinshowedthattheadsorptionprocessInasalinesystem,theadsorptionattheinterfacewasstrictly64ofthepolymerattheinterfacewasdiffusion-controlled.ForlimitedduetotheformationofbulkierSEKLclusters.SEKLthissystem,thesurfaceloadingbasedonGibbsadsorptionledtostrongstabilityagainstaphaseseparationviaincreasingisothermswasreportedtobe12.3KTfortheAcrysolthebulkconcentrationandionicstrength,whichwere64polymer.Inanotherstudy,thecomparisonbetweentheconfirmedbyaconsiderabledecreaseintheoildropletsizeemulsifyingpropertiesofligninderivatives(kraftLAandandinstabilityindicesundercentrifugalforces.ThedecreaseincalciumlignosulfonateLG)andwheyproteinWPIillustratedtheζ-potentialofemulsionsinsalt-freesystemssuggestedthatthebetteremulsifyingpropertiesofthemorehydrophobicthemechanismbehindthestabilizationofdropletswouldbepolymer(LA),whichformedsmalleroildropletsthatwereelectrostaticrepulsion.However,itisbelievedthatthesteric88associatedwithaprominentdeclineintheinterfacialtension.barrierisassociatedwithdropletstabilizationinsaltysystemsComparedwiththosestudies,betterhydrophobicinteractionduetotheadsorptionofbulkierpolymersatoilinterfaces.Ininthisstudyatthedecaneinterfacewasassociatedwithhigheraddition,adirectcorrelationwasexhibitedforthefirsttimeinterfacialactivityandbetteremulsifyingproperties(smalleroilbetweenoilcontactangle,surfacepressure,andsurfaceloadingdropletsandinstabilityindex).ΓofSEKLattheoilinterfaceandtheoildropletsizeand3355https://dx.doi.org/10.1021/acs.langmuir.0c03458Langmuir2021,37,3346−3358

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