Cold-Burst Method for Nanoparticle Formation with Natural Triglyceride Oils - Cholakova et al. - 2021 - Unknown

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pubs.acs.org/LangmuirArticleCold-BurstMethodforNanoparticleFormationwithNaturalTriglycerideOilsDianaCholakova,DesislavaGlushkova,SlavkaTcholakova,andNikolaiDenkov*CiteThis:https://dx.doi.org/10.1021/acs.langmuir.0c02967ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Thepreparationofnanoemulsionsoftriglycerideoilsinwaterusuallyrequireshighmechanicalenergyandsophisticatedequipment.Recently,weshowedthatα-to-β(viz.,gel-to-crystal)phasetransition,observedwithmostlipidsubstances(triglycerides,diglycerides,phospholipids,alkanes,etc.),maycausespontaneousdisintegrationofmicroparticlesoftheselipids,dispersedinaqueoussolutionsofappropriatesurfactants,intonanometerparticles/dropsusingasimplecooling/heatingcycleofthelipiddispersion(Cholakovaetal.ACSNano2020,14,8594).Inthecurrentstudy,weshowthatthis“cold-burstprocess”isobservedalsowithnaturaloilsofhighpracticalinterest,includingcoconutoil,palmkerneloil,andcocoabutter.Meandropdiametersofca.50−100nmwereachievedwithsomeofthestudiedoils.Fromtheresultsofdedicatedmodelexperiments,weconcludethatintensivenanofragmentationisobservedwhenthefollowingrequirementsaremet:(1)Thethree-phasecontactangleatthesolidlipid−water−airinterfaceisbelowca.30degrees.(2)Theequilibriumsurfacetensionofthesurfactantsolutionisbelowca.30mN/m,andthedynamicsurfacetensiondecreasesrapidly.(3)Thesurfactantsolutioncontainsnonsphericalsurfactantmicelles,e.g.,ellipsoidalmicellesorbiggersupramolecularaggregates.(4)Thethree-phasecontactanglemeasuredatthecontactline(frozenoil−surfactantsolution−meltedoil)isalsorelativelylow.Themechanism(s)oftheparticleburstingprocessisrevealed,andonthisbasis,theroleofallofthesefactorsisclarifiedanddiscussed.Weexplainallmaineffectsobservedexperimentallyanddefineguidingprinciplesforoptimizationofthecold-burstprocessinvarious,practicallyrelevantlipid−surfactantsystems.■INTRODUCTIONtransition),thecrystallineorderchangestothethermodynami-8−11Theproductionofsubmicrometeremulsiondropletsusuallycallymorestableβ'andβ-phases(Figure2a).Thisphaserequireshighmechanicalenergy.Microfluidizersandhigh-transformationisaccompaniedbylocalshrinkageofthelipidpressurehomogenizersareusedinwhichmostoftheenergyisphase,thusleadingtoformationof“nanovoids”betweenthelostasheatandsoundlessthan0.01%oftheenergyinputisnewlyformedcrystallinedomainsoftheβ-phase.Inotherwords,consumedfortheactualdropbreak-upandtherelatedincreaseaftertheα→β'→βphasetransition,thelipidphaseacquires1theinternalstructureofcrystallinedomains,separatedbyaofdropsurfaceareaandenergy.Severallow-energymethods7wereproposedintheliterature,includingphaseinversionnanoporousnetwork.TheformednanovoidswerereportedtoDownloadedviaUNIVOFCALIFORNIASANTABARBARAonMay16,2021at07:50:40(UTC).Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.temperature,phaseinversioncomposition,solventdiffusionhavereducedpressure(theso-called“negativepressuremethod,andself-emulsificationuponcoolingand/orheatingof12−14effect”).Inaqueoussurfactantsolutions,thisnegativealkane-in-wateremulsions,eachofthemhavingsome7pressuresucksthesurroundingaqueousphase.Dependingon2−6advantagesanddisadvantages.thespecificsurfactants,uponstorageoruponheating,thelipidRecently,wediscoveredanewefficientmethodforparticlesincreasetheirvolume,andfinally,eachofthemspontaneousburstingoflipidparticles(aso-called“cold-disintegrates(bursts)intomillionsofsmallerparticulates.7burst”process)whichresultedinadropsizedecreasefromca.Inourpreviousstudy,wefoundthatthecold-burstprocessis100to0.4μmafteronecoolingandheatingcycleonlyoftheobservedwithsurfactants,ensuringalowthree-phasecontactlipiddispersion;seeFigure1andMovieS1forillustrativeangleatthesolidtriglyceride−water−aircontactline,ca.<50−7examples.Briefly,themechanismofthecold-burstprocessisthefollowing.Uponfastcooling,manylipids,e.g.,triacylglycer-ols(triglycerides,viz.,estersderivedfromglycerolandthreeReceived:October12,2020fattyacids)ordiacylglycerols(diglycerides,estersderivedfromRevised:February3,2021glycerolandtwofattyacids),crystallizeintothethermodynami-callymetastableα-polymorphphasewhichhasahexagonalcrystallinelattice.Uponstorageatlowtemperature(solid-statephasetransition)oruponheating(melt-mediatedphase©XXXXAmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.langmuir.0c02967ALangmuirXXXX,XXX,XXX−XXX

1Langmuirpubs.acs.org/LangmuirArticleFigure1.Cold-burstprocessobservedwithpuretriglyceridesandmodeltriglyceridemixtures.(a)Schematicsofthemechanismofthecold-burstingprocess.Uponcooling,TGdropsfreezeinthemetastableα-polymorphwhichthentransformsintothestableβ-polymorph.Thistransitionisaccompaniedbyvolumeshrinkageofthecrystallinedomainsandformationofananoporousstructureinsidethelipidparticle.Uponprolongedstorageoruponheating,thesurroundingaqueousphasepenetratesintothefrozenparticlesandfragmentsthemintomillionsofnanometer-sizedlipidparticles.Uponfurtherheating,theseparticlesmeltformingnanodroplets.ThisschemeisadaptedfromFigure3inref7.(b)Illustrationofthecold-burstasobservedwithtrilaurindrops(C12TG)dispersedinanaqueoussolutionof1.5wt%C12SorbEO20and0.5wt%C18:1EO2surfactants.Uponheating,theaqueousphasepenetratesinsidetheparticleswhichincreasestheirvolume.At27°C,thesmallerlipidparticleshavealreadydisintegrated,anduponfurtherheatingupto45°C,thebiggerlipidparticlesdisintegratecompletelyaswell.Scalebars,50μm.Figure2.DSCthermogramsforbulkC12TG(a)andCNO(b).Notationsonthegraphsshowthephasetransitionscorrespondingtotheobservedpeaks,asexplainedinthetext.First,themetastableαorβ'phasesareformeduponcooling.Thebluecurvesshowthepeaksobservedupon5́°C/mincoolingandtheredcurvesthepeaksupon5°C/minheating.With“L”wedenotetheisotropicliquidphase.First,thecoolingcurvesareobtained,andafterward,thesamesamplesareheateduntiltheircompletemelting.60°,whereasforsystemswithahighcontactangle(>90−100°),rangeofmeltingtemperatures,wouldcreateananoporousweobservedtheentrapmentofthepenetratedwaterinsidethestructureabletosustainnegativepressureandtoundergocold-lipidglobuleinthemomentofitsmelting,withtheresultingburstfragmentation.formationofadoubleemulsioncontainingwater-in-oil-in-waterFromtheliterature,weknowthat,uponcooling,theCNO7drops.firstfreezesintheα-phasewithalamellaspacingof3.84nmand20Inourfirststudy,thecold-burstprocesswasdemonstratedWAXDpeakat0.412nm.Theβ′polymorphwithlamellawithpuretriglycerides(TGs),severalbinaryandternaryTGdistance3.29nmandshortspacingsat0.429and0.383nm7mixtures,diglycerides,andalkanes.However,thenaturalappearsatlowertemperaturesandcoexistswiththeα-20triglycerideswithahighcontentofsaturatedalkylchains,suchaspolymorph.ThesephasesareobservedbyDSCanalysistococonutoil(CNO),palmkerneloil(PKO),cocoabutter(CB),crystallizeseparatelyuponquickcoolingofCNO(seeFigureandlard,areverycomplexmixturesoftriglycerideswhich2b).Uponheating,thetwopolymorphstransformintoanothercontainmanydifferentalkylchains.Forexample,thetypicalβ′phasewithalamellarspacingof3.35nmandthreeWAXD20chain-lengthdistributioninthecoconutoilis48.2%C12,19.5%peaksat0.430,0.416,and0.384nm.Thispolymorph15−17C14,9%C16,7.9%C8,6%C18:1,5.8%C10,and3.6%others.transformationisalsoobservedintheDSCthermogramsasaAbout22%ofthetriglyceridesinCNOconsistoftrilaurinwithshoulderpeak,whichisfollowedbyabroadpeakreflectingthethreeC12chains,ca.33%havetwolauricchains(C12)andonecompletemeltingofthecoconutoil(seeFigure2).differentchain(C10orC14),ca.15%havetwocapricchainsTheappearanceofpolymorphsinCNOopensthepossibility(C10)andonelauricchain,10%havetwomyristicchains(C14)forobservingthecold-burstprocesswithnaturaltriglycerideandonelauricchain,andtheremaining20%havevariousotheroils,buttheconditionsforitsrealizationareunclear.Inthecombinationsofchains;seeTableS1forthedetailedcurrentstudy,weexplorethispossibilityanddefinetheguiding15−19compositionofthestudiedoils.Therefore,itisnotobviousrulesfortheoptimizationofthisprocess.Weshowthatboththeinadvancewhetherthefreezingpatternofsuchcomplextotalsurfactantconcentrationandtheratioofoil-solubletotriglyceridemixtures,containingcomponentswithaverywidewater-solublesurfactantintheaqueousphaseplaykeyrolesforBhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

2Langmuirpubs.acs.org/LangmuirArticletheprocessefficiency.Furthermore,someminorcomponents(TCIChemicals),andsorbitanmonoalkylatesfromtheSpanseries,presentinthetechnicalgradesurfactantswerefoundtoplayadenotedasCnSorbinthetext,werealsotested.Weusedrole.Werevealthemechanisms,explaintheobservedtrends,monoacylglycerideswithdifferentchainlengths:C8MGtoC18MGandshowthatthemainfindingsaregeneralandcanbeappliedandtheunsaturatedmonooleinglyceride,C18:1MG.Inseveralexperi-toothernaturaloils(cocoabutter,palmkerneloil,etc.).mentsweusedfattyacidsorfattyalcohols(CnAc,CnOH)ascosurfactants.WehavechosenCNOforthesystematicpartofthestudy,Allsubstanceswereusedasreceived,exceptfor1-oleoyl-rac-glycerolbecauseitiswellcharacterizedintheliteratureandwidelyused>40%,purchasedbySigma-Aldrich,whichwaspurifiedasdescribedininvariousindustrialapplications:forexample,infoodsforthetheMethodssectionbelow.Theaqueoussolutionswerepreparedwithpreparationofchocolate,icecream,andotherconfectionarydeionizedwaterwithresistivity>18MΩcm,purifiedbytheElix321−24products;incosmeticsasakeyingredientincreams,module(Millipore).25,26OtherChemicals.Theanhydrouscalciumchloride(purity99.5%)shampoos,lipglosses,bodymoisturizers,etc.;inthefuelindustryasanalternativesourcefortheproductionofbiodieselwasaproductofFerakBerlinGmbH.Thehydrochloricacid,potassiumandasanenvironmentallyfriendlylubricant;27,28andinthehydroxide,ethanol,andethyleneglycolwerepurchasedfromTeokompharmacyasasolubilizingexcipientfororalandinjectableandwereofanalyticalgrade.29,30Methods.EmulsionPreparation.Theinitialpolydisperseoil-in-formulations.VariousstudiessuggestedalsothatCNOmaywateremulsions,containingmicrometerdrops,werepreparedviaprovidehealthbenefits,suchashearthealthsupport,memoryrotor−statorhomogenizationwithUltraTurrax(IKA).Insomeenhancement,improvementinimmunity,andpossiblyexperiments,wepreparedamonodisperseemulsionbymembraneprevention/delayofthedevelopmentofAlzheimer’sandemulsification,passingtheoilyphasethroughporousglass31,32Parkinson’sdiseases.membranes.39,40WeusedalaboratoryMicrokitmembraneemulsifi-cationmodulefromShirasuPorousGlassTechnology(SPG,Miyazaki),workingwithtubularglassmembranesofouterdiameter■EXPERIMENTALSECTION10mmandworkingareaofapproximately3cm2.ThetemperaturewasMaterials.Oils.Forpreparationoftheemulsions,weusedcoconutkeptsufficientlyhightomaintaintheliquidstateofallsubstancesduringoil(CNO)producedbySmartOrganic,Bulgaria(underthebrandtheemulsificationprocess.DragonSuperfoods),purchasedfromalocalgrocerystore.WealsoOpticalObservationsinaGlassCapillary.Observationsbyopticaltestedseveralothersourcesofcoconutoil,includingcoconutoilfrommicroscopywereperformedwithspecimensofthestudiedemulsions,Cocosnucifera,purchasedfromSigma-Aldrich.Wedidnotobserveanyplacedinglasscapillarieswithalengthof50mmandrectangularcross-significantdifferencesbetweenthesamplespreparedfromdifferentsection:widthof1or2mmandheightof0.1mm.ThesecapillariesCNOsources.Westudiedalsopalmkerneloil(denotedasPKO,18,19wereenclosedinsideacustom-madethermostattingaluminumproducedbyBiOrigins)andcocoabutter(CB,DragonSuper-33,34chamber,withseveralorificescutoutforopticalobservation.Thefoods).CNO,PKO,andCBarenaturallyoccurringtriglyceridechambertemperaturewascontrolledbyacryothermostat(JULABOcompoundswithmixedtriglyceridechainsandapredominantcontentCF30).Thetemperatureinthechamberwasmeasuredwithaofsaturatedalkylchains(seeTableS1).thermocoupleprobe,withanaccuracyof±0.2°C,andcalibratedwithaInanotherseriesofexperiments,westudiedcommerciallyavailableprecisemercurythermometer.ThethermoprobewasinsertedinoneofPrecirolATO5(PRE)andGelucire43/01(GEL01)oils,boththeorificesofthethermostatingchamber,whereacapillarywithproductsofGattefosse.Thesecompoundsareusuallyappliedinemulsionsamplewouldbenormallypositioned.Theactualcapillariespharmaceuticalproductsforthepreparationofsolidlipidnanoparticles,withspecimensofthestudiedemulsionswereplacedintheneighboringnanocarriers,matricesforsustainedrelease,andcoatingsforprotection35−38orificesforopticalobservations.Incontrolexperiments,dispersionsandtastemasking.PREisamixtureofC16−C18monoglyceridescontaininglipidmicroparticleswereheatedtoobservetheirmelting.(MGs),diglycerides(DGs),andtriglycerides(TGs),withaThemeltingprocesswasalwaysobservedattemperaturesveryclose,predominantDGfraction(MG:DG:TG=21:54:25aswedeterminedbygaschromatography).GEL01containstriglyceridesonlyandhasawithin±0.2°C,tothereportedmeltingtemperatureofthebulkoil,Tm.TheseobservationswereperformedonanAxioImager.M2msimilarcompositiontoCNO,butwithahighercontentoflongeralkylmicroscope(Zeiss)intransmitted,cross-polarizedwhitelight,withchains(seeTableS1).anincludedλ-compensatorplatesituatedafterthesampleandbeforeIncontrolexperiments,weusedglyceryltridodecanoate(trilaurin)theanalyzer,at45°withrespecttoboththeanalyzerandthepolarizer.oilandtritetradecanoate(trimyristin)withpurity>98%and>95%,respectively,purchasedfromTCIChemicals.Inthethree-phaseTheimagesusedfordeterminationoftheinitialdropsizeweremadeincontactanglemeasurements,wealsousedmedium-chaintriglyceridetransmittedwhitelight.Long-focusobjectives×10,×20,×50,andoil(KollisolvMCT70),purchasedfromBASF.×100wereused.Allstudiedoilsareapprovedforfood,cosmetic,andpharmaceuticalThree-PhaseContactAngleMeasurements.Thesolidlipidapplications.substrates,usedformeasurementsofthecontactangles,werepreparedSurfactants.Foremulsionstabilizationweusedvariouswater-byplacingasmallamountofmeltedC14TG,CNO,orCNO+0.5wt%solubleandoil-solublesurfactants.AdetaileddescriptionoftheirC18:1MGontoaprehydrophobizedglassslide(theprehydrophobiza-chemicalstructures,producers,andpropertiesispresentedinTableS2.tionwasmadewithhexamethyldisilazane,HMDS).Afterthat,asecondThetestednonionicwater-solublesurfactantsincludepolyoxyethyleneglassslidewasplacedontopofthemeltedoiltoformalipidlayerofalkyletherswithgeneralformulaCnEOm(fromtheserieswithtradehomogeneousthickness.Afterward,theselipidlayerswerecrystallizednameBrijorLutensol),withhydrophobicchainlength,n,variedat0°CforCNOandat20°CforC14TGandstoredinafreezerat−18between8and18Catomsandnumberofethoxyunits,m,varied°Cpriortotheactualcontactangleexperiments.between2and23.WealsotesteddifferentpolyoxyethylenesorbitanThethree-phasecontactanglesatthesolidlipid−water−airinterfacemonoalkylates,CnSorbEO20(tradenameTween).WealsousedfourweremeasuredasafunctionofthetemperaturewithDSA30andDSAanionicsurfactants:twosodiumalkylsulfates,CH3(CH2)7SO4Naand100Eapparatus(Krüss).TheseexperimentsweremadebyplacingaCH3(CH2)11SO4Na,SDS,sodiumlaurylethersulfatewithoneethoxysmalldropofthestudiedsurfactantsolutiononthetopsurfaceofthegroup(SLES),sodiumdodecylbenzenesulfonate(LAS),andoneCNOsubstrate.ThetemperaturewascontrolledbyaTC40amphotericsurfactantcocoamidopropylbetaine(CAPB).thermostaticcellandmeasuredwithacalibratedthermocouple.TheSeveralseriesofoil-solublesurfactantsandcosurfactantswerealsoexperimentswereperformedfromaninitialtemperatureofT≈7°Cupstudied.TheyincludethreesurfactantsfromtheBrijseries,CnEOm,toca.22°CwhentheCNOsubstratesstartedtomelt.Allexperimentswithnvariedbetween12and18,andmvariedbetween2and4.wereperformedwitha0.5°C/minheatingrate,mimickingthePolyoxyethyleneglycolmonooleyletherwith2EOunits,C18:1EO2conditionsintheopticalobservationsoftheemulsions.Chttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

3Langmuirpubs.acs.org/LangmuirArticleFigure3.Main“elementary”mechanismsdrivingthewaterinfluxintothelipidparticlesinthecold-burstprocess.(a)Wettingofthenanoporesbytheaqueoussurfactantsolution,governedbythethree-phasecontactangle,θ,formedatthecontactlinesolidlipid−surfactantsolution−air.(b)Modelexperimentusedtomeasureθ.Inthecurrentstudy,wefoundthatthekineticsofsurfactantadsorptionσ(t)isalsoimportanttoensuretherapiddecreaseofθ.(c)Wettingoftheinternalsurfaceofthesolidlipidshellinapartiallymeltedlipidglobule,governedbythethree-phasecontactangle,α,formedatthecontactlinefrozenlipid−surfactantsolution−liquidoil.(d)Modelexperimentusedtomeasureα.(e)Changeinthesizeofthesurfactantaggregatesupontheirpenetrationthroughthenanoporeswiththeformationofahighernumberofsmallermicelleswhichcreatehigherosmoticpressurethantheoriginalsurfactantsolution.(f)Dynamiclightscatteringwasusedtodeterminethesizeofthesurfactantmicelles.Themostefficientparticledisintegrationwasobservedwhenallthreemechanismswereoperative.Theschematicsarenotinscaleandillustratethemainprocessesonly.Thethree-phasecontactanglemeasurementsatthefrozenoil−aliquotof1mLoftheemulsionwasseparatedandstoredatroomwater−meltedoil−contactlinewereperformedwithC14TGsubstrates,temperature.Theobtaineddisintegratedspecimenswerefirststudiedplacedinaglasscuvette.Ontopofthesolidlipidsubstrate,weplacedaunderopticalmicroscopetodeterminequalitativelywhethermicro-dropoftheliquidMCToil,andafterward,wepouredgentlythestudiedmeter-sizeddropletshadremainedinthesamples.Theexactdrop-sizesurfactantsolutionusingasyringe.Thethree-phasecontactangledistributionwasthenmeasuredviadynamiclightscattering(DLS).formedwasmonitoredfor5minatatemperatureof25°C.DynamicLightScattering(DLS)MeasurementsofDrop-SizeAllvaluesofthemeasuredthree-phasecontactanglespresentedinDistributionandMeanDropSize.Themeandropsizeafteronetothemanuscriptaremeasuredthroughtheaqueousphase.severalconsecutivefreeze−thawcycleswasdeterminedbyDLSDifferentialScanningCalorimetry(DSC).Thephasebehaviorofmeasurementsonthe4700Cinstrument(MalvernInstruments),CNOandC12TGwasstudiedwithDSConaDSC250apparatus(TAequippedwithasolidstatelaser,operatingat514nm.Thebuilt-inInstruments).Beforemeasurements,eachsamplewasweighted,placedmultimodalsoftwarewasusedforanalysisoftheautocorrelationintoaDSCpan(Tzeropan,TAInstruments),andsealedwithafunctionofthescatteredlight.hermeticlid(Tzerohermeticlid,TAInstruments)onaTzerosamplePurificationoftheCommercialMonooleinSampleofTechnicalpress.Thesampleswerecooledandheatedatafixedrate,variedGrade.Tostudythedifferencebetweenhighlypurifiedmonoolein(1-between0.5and5°C/min.TheDSCcurvesuponbothcoolingandoleoyl-rac-glycerol≥99%,Sigma-Aldrich)anditstechnicalgradeheatingwererecorded.Thepeakintegrationofthecurveswasanalogues(1-oleoyl-rac-glycerol40%,Sigma-Aldrich;Peceol,Gatte-performedusingthebuilt-infunctionsoftheTRIOSdataanalysisfosse;AldoMO,Lonza;andmonoolein40%,TCIChemicals),weusedsoftware(TAInstruments).aqueousalcoholextractionforthe40%1-oleoyl-rac-glycerol(Sigma-EquilibriumSurfaceTension(SFT)andDynamicSurfaceTensionAldrich).Forconvenience,thelattersubstanceisdenotedhereafteras(DST).Theequilibriumsurfacetensions(SFTs)ofthesurfactantGMO40.TheprocedureusedforGMO40purificationwassuggestedby41solutionsweremeasuredbytheWilhelmyplatemethodonaK100Sanchezetal.,andweslightlymodifiedittobetterfitourpurpose.tensiometer(KrüssGmbH)at10and20°C.Forsomeofthesystems,Briefly,weprepareda10wt%dispersionofGMO40inaqueouswemeasuredthesurfacetensionsalsobydropshapeanalysisonaethanolsolution,containing65wt%ethanoland35wt%water(65wtDSA30tensiometer(KrüssGmbH).Theresultsobtainedwiththe%aqueousethanol).TheGMO40dispersionwasstirredintensivelyat5Wilhelmyplateandthedropshapeanalysismethodswereinverygood°Cfor2h.Then,itwascentrifugedfor1hat5°Candataagreement.TheonlyexceptionwasC12SorbEO20+C18:1DGsolutioncentrifugationspeedof5000rpm.Aftercentrifugation,thesedimentduetotheveryslowadsorptionkineticsofC18:1DGtothesurface.Forwhichcontainedpredominantlythediglyceridefractionwasdispersedthisspecificsystem,thevaluesfromthedropshapeanalysismethodareagaininto65wt%aqueousethanol,andthedescribedprocedurewaspresentinthetext.repeatedtwiceatahighertemperatureof15°C.ThefinalsolidlipidMeasurementsofdynamicsurfacetension(DST)ofthesurfactantfractionseparatedafterthisprocedure,containing≈80%DGasprovensolutionswereperformedat20°CbythemaximumbubblepressurebyGCanalysis.methodonaBP2tensiometer(KrüssGmbH).Forsomeofthesystems,TheupperphaseobtainedaftertheinitialcentrifugationcontainedwemeasuredtheDSTalsoat10°C.Theresultsobtainedatthesetwopredominantlythemonoglyceridefraction.Aftercentrifugation,itwastemperatureswerewithintheframeofourexperimentalaccuracy(±0.5carefullydecantedandplacedintoanotherbottle.Then,theethanol−mN/m).watermixturewasevaporatedfullyfor2hat50°C.TheobtainedsolidFreeze−ThawingoftheLipidDropsinBulkEmulsionSamples.phasewasredissolvedin95wt%ethanolsolution,stirredfor2hat5°C,Thedropsizeevolutioninbulkemulsionswasstudiedwitheither10orandcentrifugedat15°Cfor1h.Then,theupperphasewasagain20mLsamples,placedinenclosedglasscontainers.Eachfreeze−thawseparated,andtheethanolwasevaporatedfromitat50°C.Thus,thecycleconsistedofthefollowingsteps:First,thebulksampleswereobtainedlipidfractioncontained≥90%monoglycerides.cooledinafreezerfor10−15mintoensurethataninternaltemperatureGasChromatography(GC)Analysis.Toanalyzethecommercialof1−2°Cwasreachedatwhichthelipiddrops,predispersedintheoilsandthefractionspreparedafterGMO40purification,weusedGCsurfactantsolution,frozeintosolidlipidparticles.Next,theglassanalysiswithbothhydrolyzedandnonhydrolyzedsamples.TheanalysiscontainersweretransferredintoacryothermostatandweregraduallyofnonhydrolyzedsamplesgivesinformationabouttheMG,DG,andheatedwitharateof0.5°C/minuptoseveraldegreesabovethemeltingTGcontentofthesamples,whereastheanalysisofthehydrolyzedpointoftheoil.Nofreezingoftheaqueousphasewasallowedinthesesamplesgivesinformationaboutthechainlengthdistributionofallofexperiments.Aftereachfreeze−thawcycleforthelipidparticles,anthesecomponents.Dhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

4Langmuirpubs.acs.org/LangmuirArticleFigure4.OpticalmicroscopyexperimentswithCNOdrops,dispersedin1.5wt%C12SorbEO20intheabsence(a)andinthepresence(b,c)of0.5wt%C18:1MG.(a)ParticlesstabilizedbyC12SorbEO20surfactantonlydonotdisintegrateuponheating.(b)15μmparticlesdisintegratecompletelyuponheating.(c)Disintegrationwith33μmparticlesproceedsviatwocoupledmechanisms:initially,smallliquiddropletsareejectedfromtheparticleinterior(seethewhitearrowsat16°C);uponfurtherheating,thesolidshelloftheparticlesdisintegratescompletely.Thesizeofthedropsisreducedsignificantly,butsomemicrometer-sizeddropsremainaftertheparticlecompletesmelting.Allexperimentsareperformedwithaheatingrateof0.5°C/min.Scalebarsinallimages,20μm.Nonhydrolyzedsamplesweredissolvedinchloroformandanalyzedobservedwhenthecontactangleissmallerthanca.50−60°,byan8890GCSystem(Agilent).Acomparisonbetweenthewhereasdoublewater-in-oil-in-wateremulsiondropletsforminretardationtimeforstandards(highlypurifiedacylglycerides)andthethemomentoflipidmeltingwhenthisangleishigherthanca.analyzedsamplewasusedforthepeaks’identification.90−100°.TheroleoftheangleθandtheusedmethodforitsThesampleswerehydrolyzedbyaprocedure,adaptedfromIUPAC42,43measurementareschematicallyillustratedinFigure3a,b.standardmethodsforanalysis.Thestudiedsamplewasdissolvedat5wt%in3.33MKOHsolutionin80%aqueousethanol.ThissolutionThemostsignificantdifferencebetweenthemodel7wasstoredfor4hat40°Candshakeneveryhour.Afterward,thetriglycerides,studiedinourpreviouspaper,andCNOisthatsamplewasdriedinavacuumdrierand,then,dissolvedin0.37MHCl.theTGscontainingonlyonetypeofalkylchains(e.g.,Next,chloroformwasaddedforextraction,andthesamplewastrimyristine)remainsolidthroughouttheentireheatingperiodsonicatedinabathfor15min.Afterward,thesamplewascentrifugeduntilthefinalmeltingtemperatureisreached.Incontrast,CNOfor30mintoseparatewellthewater(top)andchloroform(bottom)containsamixtureofvarioustriglycerides,someofwhichmeltatphases.ThechloroformphasewascollectedwithasyringeandanalyzedamuchlowertemperaturecomparedtotheotherswhichwithGC.containlongersaturatedchains(seetheheatingDSCthermo-gramspresentedinFigure2).Therefore,uponheating,some■RESULTSANDDISCUSSIONregionsinsidethefrozenCNOparticlesmeltbeforetheothers,Inthissection,wepresentourexperimentalresultsaboutthethusformingcoexistingliquidandfrozenregionsinsidethesecold-burstphenomenon.Thesystematicexperimentsareparticles,inacertaintemperaturerangebelowthecompleteperformedwithCNOandarepresentedfirst.Wediscusstheparticlemelting.obtainedresultsinviewoftheirmechanisticunderstandingandAsexplainedbelowinrelationtothenewlyobtainedresultsclarifythemainphysicochemicalfactorswhichcontrolthecold-withCNOandtheotheroilsstudiedinthecurrentarticle,thisburstprocessandcanbeusedforitsoptimization.Afterward,widerangeofmeltingtemperaturesleadstotheappearanceofresultswithothertri-anddiglycerideoilmixturesarepresentedtwoadditionalmechanisms(Figure3c,e)whichhavenotbeentoillustratethewiderangeofpracticallyimportantlipidreportedintheexperimentswithsingletriglycerides,describedsubstancestowhichthecold-burstmethodcouldbeapplied.inref7.ThesemechanismsarediscussedinthefollowingCNOCold-BurstingwithC12SorbEO20andC18:1MGsectionstoexplainthemicroscopeobservationswiththevariousSurfactantsandTheirMixtures.Uptonow,nostudieshavesystemsstudied.Asexplainedbelow,theseadditionalmecha-beenpublishedtoclarifywhethernanovoidsareformeduponnismscanberealizedonlyiftherequirementforthemechanismcrystallizationofCNO,whereassuchaprocesswasreportedforshowninFigure3a(viz.,wettingofthenanoporesurfacebythe44surfactantsolution)isalreadyfulfilled.Inotherwords,thenewcocoabutter.Asexplainedinref7,thesenanovoidscanbefloodedbytheaqueousphasewhenappropriatesurfactantismechanismscomplementtheinitialoneand,whenpresent,used.Dependingonthethree-phasecontactangle,θ,formedatmakethecold-burstprocessmuchmoreefficientforCNOandthethree-phasecontactlinesolidlipidsubstrate−surfactantfortheothernaturaloils.Theexperimentalmethods,illustratedsolution−air,thebehaviorofthedispersedlipidparticlesuponschematicallyinFigure3d,f,wereusedtoprovetheimportancestorage/meltingisdifferent.Intensiveparticledisintegrationisoftheadditionaltwomechanisms,asexplainedbelow.Ehttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

5Langmuirpubs.acs.org/LangmuirArticleInourpreviousstudywithpuretriglycerides,weshowedthatweshowedalsothatthemulticomponentalkaneparticlesmeltedthemostefficientself-dispersionisobservedwhenwater-solublefrominsideout;i.e.,uponfreezing,theshorteralkaneswere7andoil-solublesurfactantsarecombinedintheaqueousphase.trappedpredominantlyintheparticleinterior,whereastheTherefore,inthecurrentstudywechoseonewater-solublelonger-chainalkanesformedasolidshellwithhighermeltingsurfactantallowedtobeusedinfoods,C12SorbEO20(tradetemperatureattheparticleperipheryastructurewhichwesawnameTween20),andperformedaseriesofsystematicinthecurrentexperimentswithlargeCNOparticlesaswell.experiments,combiningitwithvariousoil-solublesurfactantsEffectofC12SorbEO20andC18:1MGTotalConcentration.(seeTableS3).Forreasonsexplainedinthenextsection,weMostoftheexperimentsinthisstudywereperformedat2wt%observedthemostefficientcold-burstprocesswith99%totalsurfactantconcentrationanda3:1ratioofthewater-to-oil-C18:1MGastheoil-solublesurfactant(seeFigure4andMoviessolublesurfactants,becausethisconcentrationissufficientlyS2andS3).hightoensureacompletecoverageofthesurfaceofthenewlyOpticalObservationsofCNOParticlesinSolutionsofformedsmallparticles/droplets(uptoca.3vol%ofoilintheC12SorbEO20andC18:1MG.Intheabsenceofoil-solubleemulsion).Thisconcentrationalsoensuresstablesurfactantsurfactant,thefrozenCNOparticlesdispersedinC12SorbEO20solutionswhichdonotphase-separateuponprolongedshelf-solutionmelteddirectly,returningtotheinitialemulsiondropsstorage.(Figure4a).WhenC18:1MGsurfactantwaspresentintheToclarifytheeffectofsurfactantconcentration,weperformedaqueoussolution,theparticlebehaviorwasverydifferent.Inmodelexperimentsalsowith1and0.5wt%totalsurfactanttheseexperiments,weusuallycooledthesamplequicklyfrom25concentration,atthesame3:1surfactantratio.With1wt%,theto2°Cwithacoolingrateofca.2.5°C/sandthenstartedtheself-dispersionefficiencywasalmostunchanged,comparedtoheatingwith0.5°C/min.Dependingontheinitialdropsize,thetheonewith2wt%.At0.5wt%,thecold-burstingprocesswasfrozenparticlesbegantodisintegrateatatemperaturearound12stillobservedwithsomesmalldropletsseparatingfromthe±2°C,withnumeroussmalllipidparticlesdetachingfromthefrozenparticleperiphery.However,thefinaldropsizeremainedperipheryofeachoriginalbigparticle.Theprocessbecamemoremuchbiggerinthelatterexperimentcomparedwiththeintensivewiththeincreaseoftemperature(seeFigure4b,c).Inexperimentsathighersurfactantconcentrations.Atsurfactanttheexperimentswith≤20μmdrops,theparticlesdisintegratedconcentrationslowerthan0.5wt%,thecold-burstprocesswascompletelyat18−19°Cintonumerous,muchsmallerparticles,notobserved.Ontheotherhand,attotalsurfactantduetothepenetrationoftheaqueousphase(Figure4b).Theseconcentrations>2wt%,thecold-burstingprocesswasobservedobservationscorrespondtothecombinationofmechanisms1untiltheaqueoussolutionbecamegelled(aroundca.6wt%),and3,asillustratedinFigure3a,e.duetotheentanglementofthethreadlikemicellesformedinWithCNOparticlesthatwerebiggerinsize(diameter>20suchhighlyconcentratedsurfactantsolutions.μm),twosimultaneousprocesseswereobserved(seeMovieS3EffectsoftheRatioofC12SorbEO20toC18:1MGandoftheandFigure4c).TogetherwiththedetachmentofthesmallPhaseinWhichC18:1MGIsDissolvedInitially.Weobservedparticlesfromtheparticleperiphery,describedabove,weefficientcold-burstingwithC12SorbEO20whenC18:1MGwasobservedalsoaphaseseparationoftheTGfractionwithalowerdispersedintheaqueousphaseorinboththeaqueousandthemeltingtemperaturefromtheTGfractionwithahighermeltingoilyphases.Incontrast,noparticleburstingwasobservedwhentemperature(i.e.,oftheTGwithshorterand/orunsaturatedtheoil-solublesurfactantwaspredissolvedintheoilyphaseonly.chainsfromthosewithsaturatedandlongeralkylchains).TheThisisrelatedtotheabilityfortherealizationofMechanism3aslow-melting-temperatureTGsspontaneouslylefttheinteriorofshownschematicallyinFigure3e.thefrozenparticleintotheaqueoussolutionintheformofsmallTheproportionofC12SorbEO20toC18:1MGwasalsoveryliquiddropletsattemperatureswhichweremuchlowerthantheimportant.AsseenfromFigure5,dependingontheratiomeltingtemperatureofthebulkCNO(seeFigure4c).Athigherbetweenthewater-solubleandoil-solublesurfactants,thetemperatures,butstilllowerthanthemeltingtemperatureoftheaqueoussurfactantsolutionsappeareddifferently(noCNObulkCNO,burstingoftheremainingsolidshellofthehigh-wasaddedinthesamplesshowninFigure5a).Thesurfactanttemperature-meltingfractionofCNOwasobserved,duetosolutionswerecompletelytransparentwhentheratiobetweenintensivepenetrationoftheaqueousphaseintothisshell.Inthisthewater-solublesurfactant,C12SorbEO20,andoil-solublecase,thecombinationofallthreemechanismsisobserved(see,surfactant,C18:1MG,was6:1orhigher.Thesurfactantsolutionse.g.,theejecteddropletsshownbywhitearrowsinFigure4cwerealmosttransparentatthe5:1ratioandopalescentat4:1whichcorrespondtoMechanism2inFigure3).and3:1ratiosandbecameveryturbidatalowerratio,viz.,ataItisworthnotingthatthefirstprocessofseparationoftheoilyhigherfractionoftheoil-solublesurfactant(Figure5).dropsfromthesolidfractionofCNOwasverysimilarinnatureTheseobservationscouldbeexplainedbythemoleculartothedewettingprocessdescribedpreviouslywithlipidglobulessurfactantaggregatesformedwhentheoil-solublesurfactantiscomposedofmixedsoybeanoil(lowmeltingtemperature)andintroducedintotheaqueoussolution.Whenthewater-solubletristearin(highmeltingtemperature),dispersedinaqueoussurfactantisinabigexcess,theoil-solublesurfactantis5surfactantsolutions.Intheselatterexperiments,areleaseofthecompletelysolubilizedinthemixedsurfactantmicelles.Theseliquidsoybeanoilfromthefrozennetworkoftristearinsurfactantsolutionsaretransparent,becausethesizeofthemicrocrystalswasobservedbyopticalmicroscopy,whenmicellesdominatedbywater-solublesurfactantsistypicallyappropriatesurfactantswereused:LAS+EO7(linearmuchsmallerthanthewavelengthofthevisiblelight,ca.5−1046alkylbenzenesulfonate+polyoxyethylenealkylether).Thisnm.Incontrast,whenthefractionofoil-solublesurfactantdewettingprocesswasdrivenbytheappropriatecontactangleofapproachesorexceedsthesolubilizationcapacityofthemicelles,thealreadymeltedoildropletsoverthe(still)frozenlipidmuchlarger,nonsphericalmixedmolecularaggregates,vesicles,substrate.Similarprocessesofspontaneousseparation(dewet-and/ormicellaragglomeratesareformedwhichhaveamuchting)oftheliquidandsolidlipidcomponentswereobservedalsobiggervolumeandhigherlightscatteringpowerthanthe45withglobulescomposedofalkanemixtures.Inthelatterstudysphericalmicellesofthewater-solublesurfactants.Asaresult,Fhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

6Langmuirpubs.acs.org/LangmuirArticleaqueousphasewasshiftedtoahigherwater--soluble/oil--solubleratio.However,cold-burstingwasobservedagainwhenthesameCNOdropsweredispersedinafreshlypreparedaqueoussolutionoftheC12SorbEO20+C18:1MGmixtureoftheappropriateratio.Theselatterresultsprovethatitisessentialforthecold-burstprocesstohavemixedmicelleswiththeappropriateratioofC12SorbEO20andC18:1MGintheaqueousphase(thepresenceofoil-solublesurfactantintheoilyphaseisofsecondaryimportance).ThisimportantobservationisrelatedtothepossibilityfortherealizationofMechanism3inFigure3e,asexplainedindetailintheMechanismoftheProcesssectionbelow.EffectofGlycerylDioleate.Theglycerylmonooleatesurfactantofhighpurity(>99%)isratherexpensive.Therefore,knowingthatthissurfactantinducesaveryefficientcold-burstprocess,wecheckedtheeffectofitsanaloguesoftechnicalgrade.Accordingtotheirproducers,themonooleinsoftechnicalgradeusuallycontain>40%C18:1MG.WetestedfourdifferentFigure5.Effectofsurfactantratioontheefficiencyofthecold-burstingmonooleinsamplesfromdifferentproducers,butsurprisingly,process.(a)Imagesofglassbottlescontainingaqueoussurfactantthecold-burstprocesswasnotobservedwitheitherofthematsolutionsof1.5wt%C12SorbEO20andC18:1MG,mixedindifferentthestandard3:1water-to-oil-solublesurfactantratioand2wt%weightratios,asindicatedontheimages(noCNOispresentinthesetotalsurfactantconcentrationalthoughthesurfactantsolutionsbottles).Thecold-burstingscoresgivenwithrednumbersonthesewereturbid(seeFigureS1).imagesrefertotheefficiencyoftheburstingprocessobservedwithThemainimpurityinthetechnicalmonooleinsistheglycerylCNOparticlesintherespectivesurfactantsolution:“0”,noparticledisintegrationobserved.“1”,smalldropletsareseparatedfromthedioleates(C18:1DG);therefore,wehypothesizedthattheirsurfaceofthefrozenparticle,butthemeandropsizedoesnotchangepresenceinterruptsthecold-burstprocessbyaffectingthesignificantly.“2,3”,allinitialdropsdisintegrateintosmallermicrometerrelevantinterfacial(surface)tensionswhichinturncontrolthedrops.“4,5”,mostofthedropsdisintegrateintomuchsmallerdropletswettingabilityofthesurfactantsolution,interruptingthewithsize<1μm,butaverysmallfractionofmicrometerdropsmayrealizationofMechanism1inFigure3(seealsotheMechanismremaininthesample.(b−d)TheimagesintheupperrowshowfrozenoftheProcesssectionbelow).CNOparticles,dispersedinthesurfactantsolutionswiththesurfactantToobtainC18:1DG,wepurifiedoneofthecommercialratioindicated.Thebottomrowshowsimagesoftheparticlesinthemonooleinsoftechnicalgrade(1-oleoyl-rac-glycerol>40%,samesamples,afteronefreeze−thawcycleofCNO:inpartb,thedropsizedecreasessignificantlyintheemulsionsstabilizedwiththeturbidSigma-Aldrich,denotedasGMO40)asdescribedintheMethods2:1surfactantmixture;thedropsizedecreaseismuchlesspronouncedsection.OurGCanalysisshowedthattheinitialGMO40sourceinpartcwhentheopalescent5:1solutionisused,whileinpartd,nocontainedca.65%MG,33%DG,and2%TG,withC18:1chainsdropdisintegrationisobservedwiththetransparent6:1solution.Thebeingthepredominantfraction≈85%.AfterthepurificationmechanisticexplanationofthisobservationisgivenlaterinthemainprocedureweobtainedseparatefractionsofC18:1MG(puritytext.Theheatingrateinalloftheseexperimentswas0.5°C/min.Scale≥90%)andC18:1DG(purity≈80%).bars,20μm.Microscopyobservationswithemulsionsstabilizedbysurfactantmixturescontainingthesefractionsconfirmed,asexpected,thatthecold-burstprocessisobservedwiththethesurfactantsolutionbecomesopalescentorturbid,andtheoil-solublesurfactantcanphase-separateuponprolongedshelf-C18:1MGfraction,whereasitwasnotobservedwiththeC18:1DGfraction.Nosignificantdifferenceswereobservedbetweenthestorage.Ourexperimentswiththesesurfactantsshowedthatcold-behavioroftheemulsions,preparedwiththeC18:1MGfractionburstingwasobservedwithallsolutionswhichwereopalescentobtainedafterGMO40purification,andthatoftheemulsionsorturbid.Incontrast,thecold-burstprocesswassuppressedpreparedwith99%pureC18:1MGpurchased.withtheopticallyclearsurfactantsolutions.Forexample,veryWealsocheckedwhethertheabsenceofthecold-burstefficientcold-burstingwasobservedat2:1and3:1ratiosofprocessinsampleswithGMO40isduetothelowerC12SorbEO20withC18:1MG(Figure5b),whereasthecold-concentrationofC18:1MGintheseexperimentscomparedtoburstingefficiencydecreasedfor4:1and5:1ratios(Figure5c)thecasewhenpureC18:1MGisaddedat0.5wt%concentration.andwasalmostcompletelysuppressedatthe6:1ratio(FigureExperimentswith1.5wt%C12SorbEO20andhigher5d).concentrationsofGMO40showedthatthisisnottheItisworthnotingthat,whenCNOemulsionwaspreparedinexplanation;viz.,nodisintegrationwasobservedforCNOC12SorbEO20+C18:1MGmixedaqueoussolutionandwasthendispersedin1.5wt%C12SorbEO20+0.8wt%GMO40solution.storedattemperaturesabovetheCNOmeltingtemperature,Thereasonfortheabsenceofdisintegrationinthesamplessomefractionoftheoil-solublesurfactantC18:1MGgraduallywithGMO40surfactantturnedouttobethat,inthepresenceoftransferredfromtheaqueousphaseintotheoilydrops.AsaC18:1DG,themoleculesofC18:1MGareincludedinmixedresult,theaqueoussurfactantsolutionbecamecompletelymicelles,whichsignificantlylowerstheirsurfaceactivity.Inturn,transparent(checkedaftertheoildropscreamedduetothisleadstoelevatedvaluesofthesurfacetensionandofthebuoyancy).Whenthisstoredemulsionwasexamined,nocold-three-phasecontactangleattheCNO−solution−airinterfaceburstingwasobserved,becausethesurfactantratiointheforC12SorbEO20+GMO40comparedtotheC12SorbEO20+Ghttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

7Langmuirpubs.acs.org/LangmuirArticleC18:1MGsolution(seeTableS3,Figure6,andtheexplanationsTheobservationthattheself-dispersionprocessisefficientofthecold-burstingmechanisminthefollowingsection).onlywhentheC18:1MGsurfactantwasdispersedintheaqueousphaseorinboththeaqueousandoilyphasesisalsoinagreementwiththecontactanglemeasurements.SimilarcontactanglesweremeasuredforC12SorbEO20onCNOandCNO+0.5wt%C18:1MGsubstrates(themonoglyceridewasdissolvedintheCNObeforeitsfreezingtopreparethesolidsubstrate;seetheemptyredcirclesinFigure6andFigureS2).WhenC18:1MGwaspresentintheaqueousphase,thecontactanglewassignificantlylower(seethefullgreencirclesinFigure6andFigureS2).Fromtheexperimentsperformedatdifferentratiosofwater-to-oil-solublesurfactants,weconcludedthatweneedanexcessfractionoftheoil-solublesurfactantintheaqueousphase,formingrelativelylargesurfactantaggregates(opalescentsolutions).Whensuchasolutionpenetratesinsidetheporousnetworkofthefrozenlipidparticle,theoil-solublesurfactantpreferentiallyadsorbsonthesurfaceofthelipidnanopores.Asaresult,thepenetratingmicellesbecomeenrichedinwater-solublesurfactantwhichleadstoshapetransformationintoFigure6.Temperaturedependenceofthecontactangles,measuredsphericalmicelleswhicharesmallerinsize(ca.6−10nminwithdropsofaqueoussurfactantsolutionsonfrozenCNOsubstrate.diameter)andmuchlargerinnumberconcentration.TheAllsolutionscontained1.5wt%C12SorbEO20.Theemptycirclesshowdifferenceinthemicellarnumberconcentrationinsidethetheresultsobtainedwithsolutionsofthiswater-solublesurfactantonly,porousnetworkofthelipidparticleandinthesurroundingmainwhereasthefullcirclesshowresultsfrommeasurementsinthepresenceaqueousphasecausesastrongosmoticeffectwhichsuckswaterofadditional0.5wt%oil-solublesurfactant:C18:1MG(green);C12EO4intothepores(seeFigure3eforaschematicpresentationofthis(purple);GMO40(orange).mechanism).Asaresultofthisosmoticeffect,theaqueousphasefloodstheparticleinterior,increasingtheparticlevolumeandtearingaparttheindividualcrystallinedomains.NotethattheMechanismoftheProcess.Agoodcorrelationbetweentheosmoticeffectisefficientonlyiftheaqueousphaseisabletothree-phasecontactangleformedatthelipid−−solution−airpenetratetheporousnetworkinthefrozenlipidparticlewhich,interfaceandthecold-burstingphenomenonwasfoundinourinturn,iscontrolledbythethree-phasecontactangle,θ,previousstudy.7Anintensivecold-burstingwasobservedwhendiscussedabove.thethree-phasecontactanglewasrelativelylow,ca.<50−60°.FromtheexperimentswithC12SorbEO20andC18:1MG,weSuchsmalleranglesfavorthewettingofthesurfaceofthesolidcanconcludethatthefollowingrequirementsshouldbefulfilledtriglyceridebythesurfactantsolution,thuspromotingtheforefficientparticleself-disintegration:penetrationoftheaqueousphaseintotheporousnetworkinside(1)Thethree-phasecontactangleattheCNO−water−airthefrozenlipidparticle(Mechanism1inFigure3).interfaceshouldbelowerthanca.35°.ToclarifythemechanismofCNOcold-burstingobservedwiththecombinationsofoil-solubleandwater-soluble(2)Themicellesinthesurfactantsolutionshouldreducetheirsurfactants,weperformedsimilarcontactanglemeasurements.aggregationnumber(size)uponadsorptionoftheoil-Anaqueoussurfactantsolutiondropwasplacedontopofasolublesurfactantonthesurfaceofthelipidnanopores.frozenCNOsubstrate,andwemeasuredthethree-phasecontactThischangeinmicelleaggregationnumbercausesanangledependenceasafunctionoftemperature(seeFigure6forosmoticpressuredifferencewhichsuckstheaqueousillustrativeresultsandFigure3bforaschematicpresentationofphaseintothefrozenparticles,leadingtotheirtheexperiment).disintegration.Theseexperimentsshowedthatthecontactangleofdropsofdeionizedwater,placedonCNOsolidsubstrate,isθ=83±1°Thedescribedmechanismalsoexplainswhynodrop(at10°C)andslightlydecreaseswhenthetemperatureisdisintegrationisobservedforC12SorbEO20+GMO40andincreasedabove18−19°C,duetotheformationofaC12SorbEO20+C18:1DGsolutions.AsseeninTableS3,theheterogenicstructureontheCNOsubstrateatthesetemper-contactangleandthesurfacetensionmeasuredwithatures(seetheDSCthermogramforbulkCNOshowninFigureC12SorbEO20solutionsarepracticallyunaffectedbytheaddition2b).Whenthesamemeasurementswereperformedwith1.5wtofC18:1DG:θCNO≈48°Candσaw≈37.7mN/mat10°C.The%C12SorbEO20aqueoussolution,thethree-phasecontactanglelattercomparisonshowsthatthesurfactantadsorptionlayerofwassignificantlylower,θ≈48±1°at10°C(emptyredcirclesC12SorbEO20remainsunaffectedbythepresenceofglycerylinFigure6).Thecontactangledecreasedto30±1°inthedioleates.TheanglemeasuredforC12SorbEO20+GMO40ispresenceof0.5wt%C18:1MG.Withthismixedsurfactantsomewhatlower,ca.38°underequivalentconditions;however,system,veryintensiveparticledisintegrationwasobserved,asthisvalueisstillmuchhigherthantheonemeasuredforexplainedabove.Forthesystem1.5wt%C12SorbEO20+0.25wtC12SorbEO20+C18:1MG,θCNO≈30°at10°C.Fromthese%C18:1MG,wemeasuredacontactangleof40±1°at10°C.results,weconcludethatthepresenceofglyceryldioleatesintheThisresultisinagoodagreementwiththeobservationthatthecommercialgrademonooleinsleadstotheformationofmixedcold-burstingwassignificantlysuppressedat0.25wt%C18:1MGC18:1MG+C18:1DGmicelleswhichsuppressthereleaseof(ratio6:1)comparedwiththeburstingobservedwith0.5wt%C18:1MGmolecules,neededtoeffectuatethecold-burstprocessC18:1MG(ratio3:1).inthissystem.Hhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

8Langmuirpubs.acs.org/LangmuirArticleFigure7.Imagesillustratingthestrongdependenceofthecold-burstprocessonthecoolingandheatingrates.Theseexperimentsareperformedwithamonodisperseemulsionofinitialdropsize≈30μm.Themostefficientdropsizedecreaseisobservedwhenafastheating−slowcoolingprotocolisapplied.Thecoolingratesaregivenwithbluelabelsandtheheatingrateswithwhitelabelsontheimages.Scalebars,20μm.Alldropsaredispersedin1.5wt%C12SorbEO20+0.5wt%C18:1MGsurfactantsolution.EffectoftheCoolingandHeatingRates.Toclarifytheeffect+1.5wt%C18:1MG,whichshowsthattheseemulsionsofthecoolingandheatingratesfortheparticledisintegration,wecontainedsufficientsurfactanttocoverthesurfaceofthenewlyperformedaseriesofexperimentswiththesameinitialformedparticlesanddroplets.monodisperseemulsion(dini≈30μm),varyingthetemperatureEffectofDifferentSurfactantsfortheCNOCold-protocol.Figure7ashowsmicroscopeimagesoftheinitialBursting.Afterweclarifiedthecold-burstingmechanismsfordroplets,whereasFigure7b−eshowsthedropletsobtainedafterCNOparticlesinC12SorbEO20+C18:1MGsolutions,weonecooling−heatingcycleatdifferentratesofcoolingandperformedaseriesofexperimentswithvarioussurfactantheating,asindicatedontheimages.combinationstovalidateourconclusionsandtoexpandourThedropsizedecreasesmostsignificantlywhenarapidunderstanding.First,wepresenttheresultsobtainedwiththecoolingandslowheatingprotocolisapplied(Figure7b).Thesamehydrophilicsurfactant,C12SorbEO20,andaseriesofoil-rapidcoolingensurestheformationofnumerousnucleiandsolublesurfactantsforcomparison.Next,wepresentresultswithsmallcrystallinedomainsinthefrozenlipidparticles.Theslowthesamehydrophobicsurfactant,C18:1MG,incombinationwithheatingensuressufficienttimefortheaqueousphasetoaseriesofnonionicwater-solublesurfactants.Finally,weshowpenetratedeepintotheparticleinteriorandtoburstthethatthesameapproachandconclusionscanbeappliedalsotoparticles.Notethesignificantdifferencebetween0.5and0.2ionicsurfactants.Thus,wedemonstratethatthecold-burst°C/minheatingrates(cf.Figure7b,c).At0.2°C/minheating,processisobservedwithaverywiderangeofsystemswhenthealldropsdisintegrateintothousandsofsubmicrometerdroplets,appropriateconditionsaremet.andsingle2−3μmdropsremaininthesample,whereasat0.5DifferentOil-SolubleSurfactantsinCombinationwith°C/minmanymicrometerdropletsremain.ThecomparisonofC12SorbEO20.AsexplainedintheMechanismoftheProcessthesamplesobtainedafterrapidorslowcooling,atafixedsectionabove,theadditionofoil-solublesurfactantintotheheatingrateof0.5°C/min(cf.Figure7c,d),showsthatmuchaqueoussolutiondecreasesthecontactangle,θ,comparedtothesmallerdropsareobservedafterfastcooling.onemeasuredwithC12SorbEO20only.ThisdecreasedependsWeconcludethatthemostefficientcold-burstprotocolisonthespecificoil-solublesurfactant.Theangledropsbyca.5°rapidcoolingandslowheating.Therefore,allotherexperimentswhenC18:1EO2(seeTableS3)orC12Sorbisaddedtowereperformedwithacoolingrateof≈2.5°C/sandheatingC12SorbEO20.However,thisdecreasewasnotsufficienttorateof0.5°C/min,unlessotherwisespecified.induceanintensivecold-bursting.MinimumAchievableDropSize.ToobtainsmallerCNOThecontactangledecreasedmoresignificantlywhenC12EO4particles,weperformedseveralconsecutivecooling−heatingorC18:1MGwasaddedintotheaqueousphase(Figure6).cycleswith1wt%CNOemulsion,containinginitially5μmHowever,forthesystem1.5wt%C12SorbEO20+0.5wt%drops,dispersed1.5wt%C12SorbEO20+0.5wt%C18:1MGC12EO4,weobservedverylimiteddisintegration(seeFiguresolution.IllustrativemicroscopyimagesoftheinitialsampleandS4).Thissurfactantiswithanintermediatehydrophobicchainoftheemulsifiedsampleafteroneandthreeconsecutiveof12carbonatoms,whichisexactlythesameasthatofthemaincooling−heatingcyclesarepresentedinFigureS3.Afterthefirstwater-solublesurfactant.Asaresult,sphericalmixedmicellesarecycle,theCNOdropshadavolume-averagediameterdV≈580formedinthepresenceofC12EO4molecules,andtherespective±80nmandnumber-averagediameterdN≈320±35nm.Aftersurfactantsolutioniscompletelytransparent.Therefore,nothesecondcooling−heatingcycle,dVdecreaseddownto≈470osmoticeffectsarepresent(Mechanism3,Figure3)inthe±25nm.Afterthreeconsecutivecooling−heatingcycles,themixedsolution1.5wt%C12SorbEO20+0.5wt%C12EO4,andmeasureddropsizesweredV≈320±15nmanddN≈170±40thecold-burstprocessisnonintensive.Toconfirmthatthenm.absenceofosmoticeffectsisthemainproblemwiththisAsexplainedintheprevioussection,thecooling−heatingsurfactantsystem,wedoubledtheC12EO4concentrationintheprotocolhasastrongimpactonthedrop-sizedistributionmixedsurfactantsolution.Indeed,thesolutionof1.5wt%obtained.Therefore,iftheprotocolisoptimizedevenfurtherC12SorbEO20+1wt%C12EO4wasopalescent,andasexpected,(e.g.,usingevenslowerheatingrates),onecanexpecttoobtaintheCNOparticlesdisintegratedcompletelyafteronefreeze−evensmallerdropletsasdemonstratedwiththeothermixedthawcycle(seeFigureS4).triglyceridecompoundsintheCold-BurstingwithOtherMixedAsimilareffectwasobservedwiththeC12SorbEO20+C10MGDi-/TriglycerideOilssectionbelow.solutions.Forthissystem,themeasuredcontactanglewasevenVerysimilarresultsaboutthemeandropdiameterswerelowerthantheoneforC12EO4andC18:1MG,ca.26±2°.obtainedalsowith5wt%CNOemulsionsinwhichtheHowever,at0.5wt%C10MG,thesurfactantsolutionwassurfactantconcentrationwastripled,i.e.,4.5wt%C12SorbEO20completelyclear,limitingtheosmoticpressureeffect.WhenweIhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

9Langmuirpubs.acs.org/LangmuirArticleFigure8.Cold-burstingofCNOparticlesinLAS+SLES±Ca2+solutions(3:1surfactantratio,1.5wt%totalconcentration,30mMCa2+).(a)Microscopyimagesillustratingthecold-burstingobservedwithCNOparticlesintheabsence(toprow)andinthepresence(bottomrow)ofCa2+.Thevolume-averageddropsizeafteronecooling−heatingcycleremainsalmostunchangedinthesamplewithoutCa2+,althoughnumeroussmalldropletshavedewettedfromtheparticleperiphery(score1.5).CompletedisintegrationisobservedinthepresenceofCa2+(score5).Scalebars,50μm.(b)Imagesofdropsofthesurfactantsolutions,placedonafrozenCNOsubstrate.TheangleattheCNO−water−aircontactlineisθ≈33°forthesamplewithoutCa2+andθ≈27°forthesamplewithCa2+at10°C.(c)ImagesofMCTdropsplacedonfrozenCTGsubstratesinthetwosurfactant14solutions.TheanglemeasuredthroughtheaqueousphasewithLAS+SLESremainsveryhighevenafter5minofimmersion,α≈155°,whileitbecomesα≈110°after1mininthesolutionwithCa2+.doubledtheC10MGconcentrationto1wt%,weobtainedC16SorbEO20,isby≈7mN/mhigherthanthatmeasuredwithopalescentsurfactantsolutionandobservedamuchmoreC12SorbEO20.Thus,weseethatthecombinationoftheintensivecold-burstingprocess.relativelyhighσ(t)forC16SorbEO20withtheslowadsorptionTherefore,fromtheseexperiments,weconfirmedthatbothofC18:1MGcouldexplainthesuppressedparticledisintegrationthecontactangle,θ,andthetypeofsurfactantaggregatesareinthissurfactantsystem.Themeasuredσ(t)forthemixturecrucialtoinduceanintensivecold-burstprocess;viz.,bothC18EO20+C18:1MGissimilartothatforC16SorbEO20+Mechanisms1and3illustratedinFigure3shouldbeoperative.C18:1MG;however,asignificantdifferenceisobservedbetweenTheosmoticeffectcouldbeensuredusingtheappropriateratiotheappearanceoftwosolutions(seeFigureS6).Therefore,theoftheoil-solubletowater-solublesurfactantswhenbiggerdifferenceinthecold-burstingscoresforthesesystemisduetomolecularaggregatesareformed,andthemixedsurfactantthedifferentosmoticpressureeffects,viz.,Mechanism3.solutionisopalescent.Incontrast,thecombinationofshort-chainwater-solubleDifferentWater-SolubleSurfactantsinCombinationwithsurfactant(C12)withanothershortchainoil-solublesurfactant,C18:1MGandC12EO4.SimilarcontactanglesweremeasuredwithC12EO4,givesmuchlowervaluesofσ(t)(seeFigureS5a).As1.5wt%ofthewater-solublesurfactantsC16SorbEO20,C12EO23,explainedabove,thissurfactantcombinationleadstoanorC18EO20,whentheywerecombinedwith0.5wt%C18:1MGintensivecold-burstprocesswhenthesurfactantsolutionsare[seeFigureS2forC16SorbEO20;theothercurvesarecompletelyopalescent,andtheosmoticpressureeffectisalsopresent.identical(notshown)].Ataheatingrateof0.5°C/min,anElucidatingtheroleofthekineticsofsurfactantadsorptionforintensivecold-burstingwasobservedinthemixturewiththecold-burstprocess,wehypothesizedthatweshouldbeableC12EO23.TheprocesswasmuchlesspronouncedforthetoobservethisprocessifweensurelongertimeforwatermixturewithC18EO20,anditwasverylimitedonlyfromthepenetrationintothelipidparticleswhenworkingwithamixtureparticlesurfaceforthemixturewithC16SorbEO20,despitetheofthelong-chainsurfactants,C16SorbEO20+C18:1MG,becauselowcontactanglemeasuredwithallofthesesurfactantmixtures.theequilibriumvaluesofσawandθforthismixtureareverycloseInanotherseriesofexperiments,wechangedtheoil-solubletothosemeasuredwiththesystemC12SorbEO20+C18:1MG.TosurfactantfromC18:1MGtoC12EO4forwhichwealsoobservedcheckthishypothesis,weperformedanadditionalexperimentlowvaluesoftheequilibriumcontactangle,θ(seeFigure6andwithCNOdropsdispersedinC16SorbEO20+C18:1MGsolutionFigureS2).Themeasuredanglesforthesethreesystemswereataslowerheatingrateof0.2°C/min.Indeed,intheseidentical(seeTableS3).Ontheotherhand,weobservedcold-experiments,wedidobserveparticledisintegration(seeFigureburstingwithsurfactantsC12SorbEO20andC12EO23,butnotS8).ItwasnotasintensiveasinthecasewithC12SorbEO20+withC18EO20attheheatingrateof0.5°C/min.C18:1MG,butitwasrathersignificant.Probably,evenslowerThecomparisonofthesevarioussurfactantsystemsindicatesheatingwouldboosttheparticledisintegration,butwedidnotthatsomeadditionalfactorshouldbetakenintoaccountwhentrysuchadditional(verytime-consuming)experiments.thesurfactantmixturecontainslong-chainwater-solubleCold-BurstingofCNOwithIonicSurfactants.Sofar,wesurfactants,e.g.,C16SorbEO20+C18:1MGorC18EO20+discussedthebehaviorofthesystemscontainingnonionicC12EO4.Tocheckwhethersomekineticeffectsareinvolved,surfactantsonly.Itiswell-knownthattheionicsurfactantsduetothelongchainofthewater-solublesurfactant,weadsorbevenfasterthanthenonionicones,becausethelifetime47measuredthedynamicsurfacetensionofthesesystems(Figuresoftheionicsurfactantmicellesisshorter.Therefore,inthisS5aandS7).Thecomparisonoftheresultsobtainedinthesection,wepresentourresultsforthecold-burstingprocesspresenceandintheabsenceofC18:1MG(emptyandfullsymbolsobservedwithtwoionicsurfactants(LASandSLES)andoneinFigureS7)showsthatC18:1MGstartstoaffectσ(t)onlyatzwitterionicsurfactant(CAPB)whicharecommonlyusedin≈800msafterthesurfaceformation.Also,theinitialvalueofhomeandpersonalcarecleaningformulations.Notethattheσ(t)atshorttimes,measuredwiththelong-chainsurfactantionicsurfactantsolutionsusedintheseexperimentscontainJhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

10Langmuirpubs.acs.org/LangmuirArticleelectrolytesofhighconcentration(30mMCaCl2addedorNaClsolution.Wenotethatinthiscasenooil-solublesurfactantispresentinthecommercialCAPB)whichsuppresstheneeded,becausetheLAS+SLESmicellesinthepresenceofelectrostaticbarrieruponadsorptionofthechargedmoleculescalciumarelargenonsphericalmolecularaggregates.oftheionicsurfactants,thusacceleratingthesurfactantFinally,wetestedtheSLES+CAPBsurfactantcombinationatadsorption.a2:1weightratioand1wt%totalsurfactantconcentration,withOneofthemostcommonlyusedionicsurfactantsforvariouscosurfactantsaddedata10timeslowerconcentrationofdetergencyandlaundryformulationsisLAS.Ithasbeenshown0.1wt%.Previousstudiesshowedthat,dependingontheaddedthatthereisaspecificinteractionbetweenCa2+ionsandthecosurfactant,theshapeandsizeoftheSLES+CAPBmicelles49headgroupsoftheLASmolecules,resultinginverylowchangesignificantly.Basedontheresultsobtainedwiththe48othersurfactants,wehypothesizedthatsuchvariationintheinterfacialtensionsattheoil−waterinterface.However,atconcentrationsmuchhigherthanthecriticalmicellarconcen-micelleshapeandsizecouldcausesignificantosmoticeffectsandtrations,thesolutionsofLAS+Ca2+areunstableata1:1molarcouldintensifythecold-burstprocess.Testedcosurfactantsratioandeasilyprecipitate.TostabilizetheLASsolutionsincludedfattyacidswithchainlengthsvariedbetweenC8andagainstprecipitation,weaddedacertainfractionofSLESwhichC14,andfattyalcoholswithchainlengthsvariedbetweenC8andisacalcium-tolerantsurfactant.Therefore,thenextseriesofC12.TheresultsaresummarizedinFigureS9.experimentswasperformedwithLAS+SLESina3:1weightWiththesystemSLES+CAPBwithoutanycosurfactant,ratio,at1.5wt%totalsurfactantconcentration,withandsomeseparationofsmalldropletsfromtheperipheryofthewithout30mMCa2+presentintheaqueousphase(seeFigurefrozenCNOparticleswasobserved,butthevolume-averaged8).dropsizeafteronecooling−heatingcycleremainedpracticallyThecontactangles,θ,measuredforbothsolutions(±Ca2+)atunchanged.Significantdifferences,however,wereobservedinthefrozenCNO−water−aircontactlinewereverylow,30±3°thepresenceofadditives.AsseenfromtheimagesinFigureS9,intheabsenceand26±2°inthepresenceofCa2+intheallofthesolutionswithadditiveswithCn>C8appearedturbid,temperaturerangebetween10and20°C(seeFigure8b).Forandasexpected,weobservedasignificantself-dispersionbothsolutions,thedynamicsurfacetensionσ(t)wasmuchlowerprocesswithallofthem(seethescorespresentedinFigureS9).thanthatoftheC12SorbEO20+C18:1MGsolution(seeFigureFromallobtainedresultswithCNOparticles,wecanS5b).However,intheabsenceofCa2+,weobservedverylimitedconcludethatthefollowingrequirementsshouldbefulfilledtoparticledisintegration.ThewholeCNOparticlesdisintegratedefficientlyobservethecold-burstprocess:completelyintonumeroussmallerparticlesinthepresenceof(1)Thethree-phasecontactangleattheoil−water−airCa2+only(seeFigure8a).Thecold-burstingefficiencyinthecontactlineshouldbelow(ca.≤30°).SuchalowvalueoflattersolutionwasevenhighercomparedtoC12SorbEO20+thecontactangleismostprobablyneededforrapidC18:1MGsolution.penetrationoftheaqueousphaseintothebranchedInagreementwiththeseexperimentalresultsandthechannelnetworkformedinthefrozenlipidparticles.50,51proposedcold-burstingmechanism,thesolutionsintheabsence2+(2)Theequilibriumsurfacetensionshouldbelow(ca.≤30ofCawerecompletelyclearatalltemperaturesstudied,mN/m),andthedynamicsurfacetensionσ(t)shouldwhereasthosewithcalciumwereopalescentatlowtemperaturesdecreaserapidly.Thelatterkineticeffectcouldbe(theybecomeclearonlyatT>15°C).overcomeinpartusingmuchlowerheatingratestoTobetterunderstandwhytheLAS+SLES+Ca2+systemensuresufficienttimeforsurfactantadsorption.performssowell,wealsomeasuredtheotherrelevantthree-(3)Ifthesurfactantsolutioncontainsnonsphericalmicellesphasecontactangle,α,i.e.,theangleatthecontactline(frozen(ellipsoidalorbiggersupramolecularaggregates),andtheCNO−surfactantsolution−justmeltedCNO),seeFigure3d.preferentialadsorptionofoneofthesurfactantscanBecauseitisnotpossibletopreparesolidCNOsubstrateandtotransformthesemicellesintosphericalones,strongplacealiquidCNOdropontopofitatagiventemperature,weosmoticeffectsareinduced,andthecold-burstprocessusedasmodelsubstratetrimyristin(C14TG)whichresemblesbecomesveryefficient.thehigh-melting-temperaturecomponentsintheCNO.Asaliquidoilydrop,weusedmedium-chaintriglycerides(MCTs)(4)Thelowthree-phasecontactanglemeasuredatthewhichmodelthelow-melting-temperaturefractioninCNO.contactline(frozenoil−water−meltedoil)alsoboostsAfterplacingtheMCToildropontopoftheCTGsubstrate,thecold-burstefficiency,facilitatingthecomplete14wepourthesurfactantsolutionsothatthesubstrateandtheseparationofthelow-andhigh-meltingfractionsoftheMCTdropbecameentirelyimmersedinthissolution.Thus,weoil.measuredthethree-phasecontactangleformedattheC14TG/TheaboverequirementscouldbefulfilledusingoneMCT/(LAS+SLES±Ca2+)contactline(Figure3d).surfactantoracombinationofseveralsurfactants(water-solubleTheresultsfromtheseexperimentsareshowninFigure8c.and/oroil-soluble)andcouldbeaffectedbythepresenceofForthesystemwithoutCa2+,thethree-phasecontactangle,α,electrolytes.becameca.155°afterthesurfactantsolutionispouredandCold-BurstingwithOtherMixedDi-/TriglycerideOils.remainsaroundthisvalueforaperiodof≈5min.Incontrast,inTotestwhethertheconclusionsreachedintheexperimentswiththesystemwithCa2+,asignificantdewettingofthesubstratebyCNOarevalidforothermixedoils(di-andtriglycerides),wetheoildropwasobserved,andthecontactanglebecame≈110°performedseveralexperimentswithpalmkerneloil(PKO),within1min.cocoabutter(CB),Gelucire43/01(GEL01),andPrecirolATOTherefore,thelowcontactangleθattheCNO−solution−air5(PRE).Thealkylchainlengthcompositionoftheseoilsiscontactline,incombinationwithlowcontactangleαatthepresentedinTableS1.(frozenoil−water−meltedoil)line,andlowσawwithfastPKOhasasimilartriglyceridecompositiontococonutoil.surfactantadsorption,characterizedbyrapidlydecreasingσ(t),ThemaindifferencebetweenPKOandCNOisthatPKOhasaexplaintheveryefficientcold-burstingintheLAS+SLES+Ca2+slightlylowercontentofCandCchainsattheexpenseofa810Khttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

11Langmuirpubs.acs.org/LangmuirArticleFigure9.Cold-burstingprocessobservedwithvariousmixedglycerideoildropletsdispersedin1.5wt%C12SorbEO20and0.5wt%C18:1MG.(a)Palmkerneloil.(b)Cocoabutter.(c)Gelucire53/01.(d)PrecirolATO5.Dropswithinitialsize≈10μmfromPKO,PRE,andGEL01disintegratecompletelyintonumeroussubmicrometerdroplets.ThedisintegrationprocessisalsoobservedforCBandisnotsoefficientunderthistemperatureprotocol(coolingto3°Candheatinguntilcompletemelting).Scalebars,10μm.higherfractionoftheC18:1chain(ca.16%inPKOvs6%inthermogram,themeltingpeakofCBstartsatca.0°CandCNO).ThepeakmeltingtemperatureofPKOisTm≈25°C,finishesat29°C,whilethefreezingpeakstartsatca.20°Candbutthecompletemeltingisobservedatca.30°C.continuesdownto−18°C.TheheatingpresentedinFigure9bCBcontainspredominantlyC16,C18,andC18:1alkylchainsstartedfromaninitialtemperatureof≈3°C.Therefore,weandhasapeakmeltingtemperature≈20°C,withcompletemeltingobservedat≈29°C.GEL01hasasimilarcompositionhypothesizedthatthelessefficientdisintegrationofCBmaybetoCNObutwithslightlylongeralkylchainsandwithouttheduetothefactthatafractionofthisoilhadnotbeencompletelyshortestchains(C6andC8).ThemainmeltingpeakisatTm≈frozenintheemulsionscooledtoca.0°C.Totestthis40°C,withashoulderobservedupto46.5°C.PREisamixturehypothesis,wepreparedCBsampledispersedinC12SorbEO20+ofmono-,di-,andtriglycerides(MG:DG:TG=21:54:25)withC18:1MGsolutioninthepresenceof50wt%ethyleneglycol.C16andC18chains;themeltingisobservedatTm,peak≈48.5°CThen,westoredthissampleinaglassbottleat−18°Covernightand56°C(doublepeak).CNO,PKO,andCBareusedinfoodandconfectionaryandmadetheheatingthemicroscopemicroscopyobservationindustries,whilePREandGEL01areusedinpharmaceuticalsthenextday.Thedisintegrationobservedinthiscasewasmuchandcosmetics.Therefore,demonstratingthatthecold-burstmorepronounced,similartotheonewithGEL01.phenomenonisapplicabletotheseoilswouldexpandPerformingexperimentswithbulksamples,wefoundthatthesignificantlytheareaoftheprocessapplications.smallestdropsizewithPREoilwasobtainedwithPRE(1wt%Illustrativeresultswithdropsoftheseoils,dispersedinemulsion),startingfromdropswithaninitialsizeof≈5μm,C12SorbEO20+C18:1MGsurfactantsolution,arepresentedinFigure9.Asseenfromthesemicroscopyimages,completedispersedinC18EO20+C12EO4solution.Withthisemulsion,wedisintegrationisobservedforPKO(Figure9a),GEL01(FigureobtaineddV≈250±50nmanddN≈15±5nmafterone9c),andPRE(Figure9d)oils,whereaswithCB(Figure9b)wecooling−heatingcycle,whiledV≈36±15nmanddN≈15nmdoobservesomecold-bursting,butmostofthedropsremainweremeasuredwiththesamesampleafter4consecutivewithmicrometersize.cooling−heatingcycles.Thesesampleswerecompletelytrans-Themostefficientdropdisintegrationwasobservedwithparent(Figure10).Weexpectthat,afterfurtheroptimizationofPRE,probablybecausethisoilcontainssaturatedC16andC18alkylchainsonly.Incontrast,CBoilcontainsahighfractionofthetemperatureprotocols,suchsmallsizescouldbeachievedunsaturatedalkylchains(ca.34%).Forthatreason,intheDSCusingasmallernumberofcycles.Lhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

12Langmuirpubs.acs.org/LangmuirArticleWiththeobtainednewresultsandtheirmechanisticexplanation,wehaveopenedthedoorfortheapplicationofthecold-burstmethodinnumerousappliedareas.Onthebasisoftheguidingprinciples,formulatedinthisstudy,onecouldapproachinarationalwayanyspecificsystemofinteresttooptimizethesurfactantsandthecooling−heatingprotocolinawayensuringtheformationofnanoparticleswithadesiredsizerange,usingaminimumnumberofcooling−heatingcycles.Theseguidingprinciplesareexpectedtoapplytoawiderangeofsurfactant−oilcombinations,becausetheyarebasedonarigorousphysicochemicalunderstandingofthephenomenainvolvedandincludetherespectivekeyphysicochemicalparametersthecontactanglesθandα,equilibriumanddynamicsurfacetensions,aggregationnumberofthesurfactantaggregates,andthecorrespondingosmoticpressureofthesurfactantsolutions.Figure10.Cold-burstingofbulksampleswith1wt%PREdropsdispersedin1.5wt%C18EO20+0.5wt%C12EO4solution.Theinitial■ASSOCIATEDCONTENTsamplecontainsparticleswithdiameter≈5μmandappearsmilky*sıSupportingInformationwhite.Thedropsizedecreasesdownto250nmafteronecooling−TheSupportingInformationisavailablefreeofchargeatheatingcycle.Themainpartofthedropsdisintegratesintothesmallesthttps://pubs.acs.org/doi/10.1021/acs.langmuir.0c02967.possiblesize,ca.20nm,after2consecutivecycles;however,somesmallfractionofparticlesremainwithhighersizesmakingtheemulsionsAdditionaldataandfiguresincludingalkylchainlengthopalescent.Afterfourconsecutivecycles,>99%ofthedropsachievecompositionofthestudiednaturaltriglycerideoils,sizedV≈20nm,andtheemulsionbecomescompletelytransparentsurfactantstructuresandproperties,equilibriumsurface(somesmallfractionoftheparticlesremainedwithbiggersizes,tensionsandthree-phasecontactangles,visualappear-increasingtheaveragedsizemeasuredbyvolumeto36nm).anceofmixedsurfactantsolutions,temperaturedepend-enceofthecontactangles,microscopyimages,dynamicsurfacetensions,andtheeffectoftheheatingrate(PDF)■CONCLUSIONSMovieS1:cold-burstingprocesswithC12TG(AVI)Thecurrentstudydemonstratesthatthecold-burstphenom-MovieS2:cold-burstingprocesswithCNO(AVI)enonobservedpreviouslywithpuretriglyceridesandwithMovieS3:cold-burstingprocesswithCNO(AVI)simplebinaryorternarymixturesofmonoacidtriglyceridesisapplicablealsotomuchmorecomplextriglyceridemixtureswith■AUTHORINFORMATIONvariousalkylchains,includingcoconutoil,palmkerneloil,cocoaCorrespondingAuthorbutter,PrecirolATO5,andGelucire43/01.NikolaiDenkov−DepartmentofChemicalandThespontaneousburstinguponheatingoffrozenoilyPharmaceuticalEngineeringFacultyofChemistryandparticles,dispersedinaqueoussurfactantsolution,isparticularlyPharmacy,SofiaUniversity,1164Sofia,Bulgaria;efficientwhenthefollowingrequirementsarefulfilled:orcid.org/0000-0003-1118-7635;Phone:+3592(1)Thesurfactantsensurethatthethree-phasecontactangle8161639;Email:nd@lcpe.uni-sofia.bg;Fax:+3592atthefrozenoil−water−aircontactlineislow,≤ca.30°.9625643(2)Theequilibriumsurfacetensionofthesurfactantsolutionislow,≤ca.30mN/m,andtherateofadsorptionisAuthorsrelativelyfast.DianaCholakova−DepartmentofChemicaland(3)Thethree-phasecontactangleatthefrozenoil−water−PharmaceuticalEngineeringFacultyofChemistryandmeltedoilcontactlineisbelowca.150°.Pharmacy,SofiaUniversity,1164Sofia,Bulgaria;(4)Theaqueoussolutioncontainslargemicellaraggregatesorcid.org/0000-0001-6654-6418whichtransformintosphericalmicelleswhensomeoftheDesislavaGlushkova−DepartmentofChemicalandsurfactantcomponentsadsorbonthesurfaceofthePharmaceuticalEngineeringFacultyofChemistryandnanoporesinthelipidparticles,thusinducingastrongPharmacy,SofiaUniversity,1164Sofia,Bulgaria;osmoticeffectwhichsuckswaterintotheparticleinterior.orcid.org/0000-0001-6077-7338Themostefficientcold-burstprotocolisrapidcooling,SlavkaTcholakova−DepartmentofChemicalandfollowedbyslowheating.Inthisprotocol,thehighcoolingratesPharmaceuticalEngineeringFacultyofChemistryandensuretheformationofsmallercrystallitesinthefrozenlipidPharmacy,SofiaUniversity,1164Sofia,Bulgaria;particles,whereastheslowerheatingensuresalongertimefororcid.org/0000-0001-8091-7529penetrationoftheaqueousphaseintotheporousnetwork,Completecontactinformationisavailableat:surfactantadsorption,anddewettingoftheliquidoilfractionhttps://pubs.acs.org/10.1021/acs.langmuir.0c02967fromthestillfrozenone.Forthemixturesofwater-andoil-solublesurfactants,theAuthorContributionscold-burstprocessisobservedonlyifthereisasufficientlyhighS.T.,N.D.,andD.C.designedthestudy.D.G.performedmostoffractionofoil-solublesurfactantdispersedintheaqueousphasetheexperiments,summarizedtheresults,andpreparedpartofwhichensurestheformationoflargemicellaraggregatesandthethefiguresandmovies.D.C.andS.T.analyzedtheresults.D.C.,osmoticeffectdescribedabove.S.T.,andN.D.clarifiedthemechanisms.D.C.preparedthefirstMhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

13Langmuirpubs.acs.org/LangmuirArticledraftofthemanuscript,whereasN.D.editeditandpreparedthe(15)Sonwai,S.;Rungprasertphol,P.;Nantipipat,N.;finaldraft.S.T.readcriticallythemanuscriptandsuggestedTungvongchatoan,S.;Laiyangkoon,N.CharacterizationofCoconutimprovements.Allauthorsparticipatedindiscussionsandoilfractionsobtainedfromsolventfractionationusingacetone.J.Oleocriticallyreadthefinalmanuscript.Sci.2017,66(9),951−961.(16)Marikkar,J.M.N.;Saraf,D.;Dzulkifly,M.H.EffectoffractionalNotescrystallizationoncompositionandthermalbehaviorofcoconutoil.Int.Theauthorsdeclarenocompetingfinancialinterest.J.FoodProp.2013,16,1284−1292.(17)Kumar,P.K.P.;Krishna,A.G.G.Physicochemicalcharacter-■isticsofcommercialcoconutoilsproducedinIndia.GrasasAceitesACKNOWLEDGMENTS2015,66,No.e062.TheauthorsthankMs.AnitaBiserova,SofiaUniversity,forher(18)Chai,X.;Meng,Z.;Jiang,J.;Cao,P.;Liang,X.;Piatko,M.;helpwithpartoftheexperimentalwork.ThecommercialgradeCampbell,S.;KoonLo,S.;Liu,Y.Non-triglyceridecomponentsmonooleinfractionationandGCanalysiswereperformedbymodulatethefatcrystalnetworkofpalmkerneloilandcoconutoil.Mr.DelyanKrastev,Mrs.MarianaBoneva-Astrukova,andDr.FoodRes.Int.2018,105,423−431.ZahariVinarov,SofiaUniversity(usingaproceduredefinedby(19)Zhang,Z.;Lee,W.J.;Zhou,H.;Wang,Y.EffectsofchemicalS.T.andD.C.);theirhelpisgratefullyacknowledged.Theinteresterificationonthetriacylglycerols,solidfatcontentsandauthorsthankMrs.DoraDimitrovaformeasuringthesurfacecrystallizationkineticsofpalmoil-basedfats.FoodFunct.2019,10,tensions.ThisstudywaspartiallyfundedbytheProof-of-7553−7564.ConceptgrantCoolNanoDrop(841827).Theauthorsgrate-(20)Mahisanunt,B.;Hondoh,H.;Ueno,S.EffectsoftripalmitinandfullyacknowledgethesupportfromtheOperationalProgramtristearinoncrystallizationandmeltingbehaviorofcoconutoil.J.Am.“ScienceandEducationforSmartGrowth”,Bulgaria,GrantOilChem.Soc.2019,96,391−404.BG05M2OP001-1.002-0023.(21)Young,F.V.K.Palmkernelandcoconutoils:Analyticalcharacteristics,processtechnologyanduses.J.Am.OilChem.Soc.1983,60,374−379.■REFERENCES(22)Rothkopf,I.;Danzl,W.Changesinchocolatecrystallizationare(1)Walstra,P.;Smulders,P.E.A.EmulsionFormation.InModerninfluencedbytypeandamountofintroducedfillinglipids.Eur.J.LipidAspectsinEmulsionScience,EmulsionFormation;Binks,B.,Ed.;TheSci.Technol.2015,117,1714−1721.RoyalSocietyofChemistry:Cambridge,1998;pp56−99.(23)Cheng,J.;Ma,Y.;Li,X.;Yan,T.;Cui,J.Effectsofmilkprotein-(2)Tadros,T.;Izquierdo,P.;Esquena,J.;Solans,C.Formulationandpolysaccharideinteractionsonthestabilityoficecreammixmodelstabilityofnano-emulsions.Adv.ColloidInterfaceSci.2004,108−109,systems.FoodHydrocolloids2015,45,327−336.303−318.(24)Granger,C.;Leger,A.;Barey,P.;Langendorff,V.;Cansell,M.(3)Anton,N.;Benoit,J.-P.;Saulnier,P.DesignandproductionofInfluenceofformulationonthestructuralnetworksinicecream.Int.nanoparticlesformulatedfromnano-emulsiontemplates-Areview.J.DairyJ.2005,15,255−262.ControlledRelease2008,128,185−199.(25)Burnett,C.L.;Bergfeld,W.F.;Belsito,D.V.;Klaassen,C.D.;(4)Li,Z.;Xu,D.;Yuan,Y.;Wu,H.;Hou,J.;Kang,W.;Bai,B.Marks,J.G.;Shank,T.J.;Slaga,T.J.;Snyder,P.W.;Andersen,F.A.AdvancesofspontaneousemulsificationanditsimportantapplicationsFinalreportonthesafetyassessmentofcocosnucifera(Coconut)oilinenhancedoilrecoveryprocess.Adv.ColloidInterfaceSci.2020,277,andrelatedingredients.Int.J.Toxicol.2011,30,5S−16S.102119.(26)Aburjai,T.;Natsheh,F.M.Plantsusedincosmetics.Phytother.(5)Tcholakova,S.;Valkova,Z.;Cholakova,D.;Vinarov,Z.;Lesov,I.;Res.2003,17,987−1000.Denkov,N.;Smoukov,S.K.Efficientself-emulsificationviacooling-(27)Hoekman,S.K.;Broch,A.;Robbins,C.;Ceniceros,E.;heatingcycles.Nat.Commun.2017,8,15012.Natarajan,M.Reviewofbiodieselcomposition,properties,and(6)Valkova,Z.;Cholakova,D.;Tcholakova,S.;Denkov,N.;specifications.RenewableSustainableEnergyRev.2012,16,143−169.Smoukov,S.K.Mechanismsandcontrolofself-emulsificationupon(28)Jayadas,N.H.;Nair,K.P.;Ajithkumar,G.Tribologicalfreezingandmeltingofdispersedalkanedrops.Langmuir2017,33,evaluationofcoconutoilasanenvironment-friendlylubricant.Tribol.12155−12170.Int.2007,40,350−354.(7)Cholakova,D.;Glushkova,D.;Tcholakova,S.;Denkov,N.(29)Grüne,L.;Bunjes,H.Self-dispersingformulationsfortheNanoporeandnanoparticlesformationwithlipidsundergoingdeliveryofpoorlysolubledrugs-Miscibilityofphophatidylcholinespolymorphicphasetransitions.ACSNano2020,14,8594−8604.withoilsandfats.Eur.J.Pharm.Biopharm.2020,151,209−219.(8)Bunjes,H.;Westesen,K.;Koch,M.H.J.Crystallizationtendency(30)Singh,B.K.S.;Narayanan,S.S.;Khor,B.H.;Sahathevan,S.;andpolymorphictransitionsintriglyceridenanoparticles.Int.J.Pharm.Gafor,A.H.A.;Fiaccadori,E.;Sundram,K.;Karupaiah,T.1996,129,159−173.Compositionandfunctionalityoflipidemulsionsinparenteral(9)Small,D.M.ThePhysicalChemistryofLipids.InFromAlkanestonutrition:examiningevidenceandclinicalapplications.Front.PhospholipidsinHandbookoflipidresearch;Plenum:NewYork,1986.Pharmacol.2020,11,506.(10)Takeuchi,M.;Ueno,S.;Sato,K.SynchrotronradiationSAXS/(31)Chatterjee,P.;Fernando,M.;Fernando,B.;Dias,C.B.;Shah,T.;WAXSstudyofpolymorph-dependentphasebehaviorofbinarySilva,R.;Williams,S.;Pedrini,S.;Hillebrandt,H.;Goozee,K.;Barin,E.;mixturesofsaturatedmonoacidtriacylglycerols.Cryst.GrowthDes.2003,3,369−374.Sohrabi,H.R.;Garg,M.;Cunnane,S.;Martins,R.N.Potentialof(11)Motoyama,M.Structureandphasecharacterizationofcoconutoilandmediumchaintriglyceridesinthepreventionandtriacylglycerolsbyramanspectroscopy.Bull.NAROInst.LivestGrassltreatmentofAlzheimer’sdisease.Mech.AgeingDev.2020,186,111209.Sci.2012,12,19−68.(32)Mischley,L.K.;Lau,R.C.;Bennett,R.D.Roleofdietand(12)Cebula,D.J.;McClements,D.J.;Povey,M.J.W.SmallanglenutritionalsupplementsinParkinson’sdiseaseprogression.Oxid.Med.neutronscatteringfromvoidsincrystallinetrilaurin.J.Am.OilChem.Cell.Longevity2017,2017(9),6405278.Soc.1990,67,76−78.(33)Bootello,M.A.;Hartel,R.W.;Garces,R.;Martines-Force,E.;(13)Lencki,R.W.;Craven,R.J.NegativepressureeffectsduringpureSalas,J.J.Evaluationofhigholeic-highstearicsunflowerhardstearinstriacylglycerolcrystallization.Cryst.GrowthDes.2012,12,4981−4986.forcocoabutterequivalentformulation.FoodChem.2012,134,1409−(14)Peyronel,F.;Quinn,B.;Marangoni,A.G.;Pink,D.A.Ultrasmall1417.angleX-rayscatteringforpuretristearinandtripalmitin:model(34)Sonwai,S.;Kaphueakngam,P.;Flood,A.Blendingofmangopredictionsandexperimentalresults.FoodBiophysics2014,9,304−kernelfatandpalmoilmid-fractiontoobtaincocoabutterequivalent.J.314.FoodSci.Technol.2014,51,2357−2369.Nhttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX

14Langmuirpubs.acs.org/LangmuirArticle(35)Schäfer-Korting,M.;Mehnert,W.;Korting,H.-C.Lipidnanoparticlesforimprovedtopicalapplicationofdrugsforskindiseases.Adv.DrugDeliveryRev.2007,59,427−443.(36)Aznar,M.A.;Lasa-Saracibar,B.;Estella-HermosodeMendoza,A.;Blanco-Prieto,M.J.Efficacyofedelfosinelipidnanoparticlesinbreastcancercells.Int.J.Pharm.2013,454,720−726.(37)Elmowafy,M.;Ibrahim,H.M.;Ahmed,M.A.;Shalaby,K.;Salama,A.;Hefesha,H.Atorvastatin-loadednanostructuredlipidcarriers(Nlcs):Strategytoovercomeoraldeliverydrawbacks.DrugDelivery2017,24,932−941.(38)Shimpi,S.;Chauhan,B.;Mahadik,K.R.;Paradkar,A.Preparationandevaluationofdiltiazemhydrochloride-Gelucire43/01floatinggranulespreparedbymeltgranulation.AAPSPharmSciTech2004,5,51−56.(39)Nakashima,T.;Shimizu,M.;Kukizaki,M.Particlecontrolofemulsionbymembraneemulsificationanditsapplications.Adv.DrugDeliveryRev.2000,45,47−56.(40)Vladisavljevic,G.T.;Williams,R.A.Recentdevelopmentinmanufacturingemulsionsandparticulateproductsusingmembranes.Adv.ColloidInterfaceSci.2005,113,1−20.(41)Sanchez,E.;Pardo-Castaño,C.;Bolaños,G.Purificationofmonoglyceridesfrompalmstearinbyliquid-liquidextractionwithaqueousethanol.J.Am.OilChem.Soc.2018,95,217−228.(42)Paquot,C.Standartmethodsfortheanalysisofoils,fatsandderivatives,6thed.;IUPAC,1981.(43)Vinarova,L.;Vinarov,Z.;Tcholakova,S.;Denkov,N.;Stoyanov,S.;Lips,A.Themechanismofloweringcholesterolabsorptionbycalciumasstudiedbyinvitrodigestionmodel.FoodFunct.2016,7,151−163.(44)Lencki,R.W.;Craven,R.J.Negativepressureinducedcavityformationduringcocoabuttercrystallization.J.Am.OilChem.Soc.2013,90,1509−1516.(45)Cholakova,D.;Valkova,Z.;Tcholakova,S.;Denkov,N.;Smoukov,S.K.Self-shaping”ofmulticomponentdrops.Langmuir2017,33,5696−5706.(46)Christov,N.C.;Danov,K.D.;Zheng,Y.;Kralchevsky,P.A.;vonKlitzing,R.Oscillatorystructuralforcesduetononionicsurfactantmicelles:Databycolloidal-probeAFMvsTheory.Langmuir2010,26,915−923.(47)Marinova,K.G.;Denkov,N.D.Foamdestructionbymixedsolid-liquidantifoamsinsolutionsofalkylglucoside:Electrostaticinteractionsanddynamiceffects.Langmuir2001,17,2426−2436.(48)Anachkov,S.E.;Tcholakova,S.;Dimitrova,D.T.;Denkov,N.D.;Subrahmaniam,N.;Bhunia,P.Adsorptionoflinearalkylbenzebesulfonatesonoil-waterinterface:EffectsofNa+,Mg2+andCa2+ions.ColloidsSurf.,A2015,466,18−27.(49)Mitrinova,Z.;Tcholakova,S.;Denkov,N.Controlofsurfactantsolutionrheologyusingmedium-chaincosurfactants.ColloidsSurf.,A2018,537,173−184.(50)Scanziani,A.;Singh,K.;Blunt,M.J.;Guadagnini,A.AutomaticmethodforestimationofinsitueffectivecontactanglefromX-raymicrotomographyimagesoftwo-phaseflowinporousmedia.J.ColloidInterfaceSci.2017,496,51−59.(51)Rücker,M.;etal.Theeffectofmixedwettabilityonpore-scaleflowregimesbasedonafloodingexperimentinkettonlimestone.Geophys.Res.Lett.2019,46,3225−3234.Ohttps://dx.doi.org/10.1021/acs.langmuir.0c02967LangmuirXXXX,XXX,XXX−XXX