Building Reversible Nano-raspberries - Eren et al. - Unknown - Unknown

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SupplementaryInformationfor:BuildingReversibleNano-raspberriesE.DenizEren1,Mohammad-AminMoradi1,HeinerFriedrich1,2andGijsbertusdeWith1*1LaboratoryofPhysicalChemistry,DepartmentofChemicalEngineeringandChemistry,EindhovenUniversityofTechnology,Eindhoven,TheNetherlands2InstituteforComplexMolecularSystems,EindhovenUniversityofTechnology,Eindhoven,TheNetherlands*Correspondenceto:G.deWith(G.deWith@tue.nl;orcid.org/0000-0002-7163-8429)MaterialsandMethodsSynthesisofsilicananoparticles100mgL-lysine(Fluka)wasdissolvedin100mlpurewaterina250mlthree-neckflaskbymagneticallystirring(270rpm)at60°C.Thereafter,theformationoftheSiO2NPswasinitiatedbyadding6mltetraethylorthosilicate(TEOS)tothereactionsolutionandthereactionvesselwasclosedoffbyarubberseptumwithasmallneedleinsertedasavent.Thereactionwasleftmeanwhilestirringfor1day.SurfacemodificationofsilicananoparticlesSilicananoparticlesneedtobesurfacemodifiedtoprovidethemwiththeproperchargedensityandasaresult,havingacontrollableinteractionforbuildingblockassemblyforthefollowingstep.Tomodifythesurfaceofsilicananoparticles,1wt%(3-Aminopropyl)triethoxysilane(APTES)(Sigma-Aldrich)solutioninwater(pH∼11)wasslowlyaddedtotheas-preparedsilicasuspensionwhilestirringvigorously(~700rpm).TheinitialamountofAPTESandcolloidalsilicausedhadasilane:silicaweightratioof1:50,abovewhichtheparticlesrapidlycoagulated.Thesilane-silicamixturewasthenwashedbyrepeatedcentrifugationandreplacementofthesupernatantforatleastfivetimes.SizemeasurementsofsilicaandpolystyrenelatexnanoparticlesSizedistributionsweredeterminedbymanuallymeasuringtheshortandlongaxesofindividualsilicananoparticles(SiO2NPs)incryoTEMimagesusinganin-housemadeMATLABscript.TheaverageradiusofaSiO2NPwastakentobeaquarterofthesumofthelongandshortaxesoftheSiO2NPandthesizeisreportedas:mean±standarddeviationofthemean(262SiO2NPswereusedtocalculatethesizedistributionandthesizewasfoundtobe28.8±0.4nm).TheresultscanbeseeninFigureSI1.

1FigureSI1.ThesizedistributionoftheSiO2NPsdeterminedfroma-b)cryoTEMimagesusinganin-housemadeMATLABscript,c)Histogramshowingthesizedistributionofsilicananoparticlesobtainedfromimageb,andd)ThenumberdistributionofthesizeofthesilicananoparticlesbeforeandaftersurfacemodificationdeterminedbyDLS.FigureSI2.ThesizedistributionofthePSLNPsdeterminedfromDLS.

2SupplementaryResultsDLSmeasurementsofsilica,polystyrenelatex,andmixturesatdifferentpHvaluesDynamiclightscattering(DLS)isatechniquethatdependsontheinteractionofthelightwiththenanoparticlesofinterestinagivensolution.ItmeasuresthediameteroftheparticlesDunderBrownianmotionbycalculatingthetime-dependentfluctuationsoftheintensityofthescatteredlight.TheoutputofDLSistheintensityweighteddistribution,whichisproportionaltoD6,whileimagingresultsinthenumberdistributionproportionaltoD0.Consideringthefactthatinoursystem,thereisapproximatelya3.5folddifferenceforthediameteroftheSiO2andPSLNPs,afactor3.56differenceinscatteringpowerintheRayleighregionresults.Therefore,thesignalcomingfrom100nmPSLNPsovershadowsthesignalwhichiscomingfrom30nmSiO2NPsintheintensityweighteddistribution.FigureSI3.Resultsobtainedfromdynamiclightscatteringanalysisbyusingindividualpolystyrenelatex,silicananoparticlesandmixtureatpH2.a)Theautocorrelationfunctiongofindividualnanoparticlesandthemixtureofpolystyrenelatexandsilicananoparticlesmixedafter2minutesatpH2,b)TheautocorrelationfunctiongofthemixtureatpH2overtime,c)Intensityweighted,andd)NumberweighteddynamiclightscatteringresultsofthemixtureatpH2showingthesizedistributionofmixturedependingonthetimeafterwhichreactionisinitiated.

3FigureSI4.Theautocorrelationfunctiongofmixturesofpolystyrenelatexandsilicananoparticlesasafunctionoftime.Dynamiclightscatteringmeasurementsobtainedmixingafter;a)2minutes,b)30minutes,c)1hour,d)1.5hours,e)6hours,andf)1month.FigureSI5.a)Zetapotentialandb)electrophoreticmobilityforPSLNPsandSiO2NPsmixturesasafunctionofpH.

4Pseudo-reversibilityofnano-raspberriesThepseudo-reversibilityofnano-raspberryassemblyanddisassemblywasevaluatedbychangingthepHofthesolutionrepeatedly.FigureSI6showsthecryoTEMandDLSresultsofthemixtureafterthe5thtimeofpHchangeandtheresultsindicatethatafteracriticalpoint,SiO2NPsandPSLNPscannotformwell-definednano-raspberriesanymoreduetotheincreasedsaltconcentration.FigureSI6.CryoTEMimagecorrespondstothepointmarkedwiththeyellowarrowwhichiscycle#5.TheoreticalConsiderationsDerjaguin-Landau-Verwey-Overbeek(DLVO)theorywasemployedtoinvestigatethecolloidalstabilityoftheindividualsilicaandpolystyrenelatexnanoparticles,andthenano-raspberriesasDLVOtheoryprovidesaquantitativetheoreticalunderstandingoftheinteractionpotentialbetweentwochargedparticlesinteractinginaliquidmedium1.AccordingtoDLVOtheory,thenetinteractionbetweentwonanoparticles(VDLVO)isthesumoftherepulsiveelectrostaticdouble-layerorCoulombinteractions(VCoul)andtheattractivevanderWaals(V1vdW)interactionpotential,sothat??DLVO=??vdW+??CoulTheelectrostaticinteractionsbetweentwosphericalobjectsofequalsurfacepotentialandequalsizeiscalculatedusingPoisson-Boltzmannformulation.1,2TheclassicalDLVOtheoryisbasedonthelinearizedPoisson-Boltzmannequationforwhichananalyticalsolutionexists2,butvariousapproximateexpressionshavebeenproposed3–5.HereweusedtheexpressionasgivenbySaderetal.5inordertocalculatetheelectrostaticinteractionpotentialbetweentwosphericalobjectsattheconstantsurfacepotentialforanydistanceregardlessoftheparticlesize:

5??2????2B2??Coul=64π��????0��??ln�1+exp(−??ℎ)�2??+ℎ????where??=exp(??ℎ/2)tan−1h(exp(−??ℎ/2)tanh(??/4))0andwhereεistherelativedielectricconstantofthesolvent,histheclosestseparationbetweenthenanoparticles’surfaces,??isthesurfacepotentialoftheparticleofinterest(whichcanbeanindividualnanoparticlesystemornano-raspberries),and??istheDebyelength,whichisdescribedinthemaintext.AbovementionedequationsaregoodapproximationsforthenumericalcalculationsofthefullPoisson-Boltzmannequationatconstantsurfacepotential6.ThevanderWaalsattractionbetweentwoparticlesofequalsizeiscalculatedaccordingtotheHamakerformulationofintermolecularforcesassumingpairwiseadditivity2.Althoughthisstillisanapproximation,itneverthelessdescribesthephysicaloriginoftheinteraction1.TheexpressionforthevanderWaalsinteractionpotentialisgivenby:??2??22??2ℎ2+4??ℎH??vdW=−6�ℎ2+4??ℎ+ℎ2+4??ℎ+4??2+ln�ℎ2+4??ℎ+4??2��whereRistheradiusoftheparticle,histheclosestseparationbetweenthenanoparticles’surfaces,andA7HistheHamakerconstant,whichquantifiesthepropertiesofthematerial.Forthecalculationweconsideronesinglenano-raspberryasaparticlecomposedofasphericalpolystyrenelatexcoreandsilicananoparticlesattachedtothecurvedsurface.TheradiusofsilicananoparticlesusedwasRSilica≅15nmwhilepolystyrenelatexcoreradiuswasRPS≅50nmwhichtotalstoanano-raspberrynanoparticlediameterofD=160nm.ForsilicaandpolystyreneA8−21910HvaluesasgivenbyBergström,AH=4.6×10J,andbyTsaurandFowkes,A−21H=5.0×10J,wereused.Fornano-raspberriescoveredwithSiO2nanoparticles,thevalueofforsilica,A−218H=4.6×10J,wasused.ThestabilityofindividualPSLNPs,SiO2NPs,andnano-raspberriesascalculatedisshowninFigureSI7.TheresultsindicatethattheSiNPshaveanenergybarrierofabout3.3kTascomparedtothePSLNPswithabout50kT.ThecalculationsfortheDLVOpotentialenergydiagramsinFigureSI7bweremadebyconsideringthefactthatPSLNPsandSiO2NPsformednano-raspberriesinthemediumatcertainpHvalues.Forexample,atpH2,weconsiderthesupraparticlefortheDLVOcalculationstobeasingleparticlewitharadiusof80nm.Ascanbeseenfromtheresults,atpH2supraparticleshaveanenergybarrierofabout1.5kT,indicatingthatnano-raspberriescannotstayseparatedfromeachotherforalongerperiodoftime,asalsoshownviacryoTEMinthemanuscript(Figure2n–2p).Moreover,theDLVOpotentialcurves

6calculatedforthenano-raspberriesandindividualnanoparticlesystemsshownumericalvaluesingoodagreementwithcalculationsmadeonsimilarsystems11,stronglyindicatingtheapplicabilityofoursystemtodifferentsizesofnanoparticlemixtures.FigureSI7.Thetotalinteractionpotentialofa)twoSiO2NPsandtwoPSLNPsasafunctionofseparationdistance,andb)nano-raspberriesatdifferentpHvalues.Obviously,thecalculationsgivenabovedonotdescribetheformationprocessofthenano-raspberries.Tomodelthatformationprocess,severalaspectsshouldbeconsidered.•Themixingentropyofthedispersionischangingasthecounter-ionsaredecoratingtheparticles.Theeffectisexpectedtobenottoolarge,butacalculationwillrequirethesurfacedensityofchargedsitesonthesurfaceoftheparticles.•Theassumptionofaconstantdielectricpermittivityasnormallyusedisunlikelytobevalidclosetothenano-raspberries,whichrendersthedecaynotexponentialasintheoriginalDLVOtheory.Instead,itbecomesclosetoarithmetic,likeelectrostaticsclosetoabilayer,asshown,forexample,inaMonteCarlosimulation12.•VariousoptionsexisttomodelthevanderWaalscontribution13.ThisrefersnotonlytotheexpressionusedforthevanderWaalsattraction,butalsototheassumedstructureoftheinteractingpartsinvolved.•Forreallysmallparticles(5-10nm)thehydrationforcesarerelevant14,15.Evenifmodeledbyanexponentialfunction,thisrequiresinformationabouttwomoreparameters.•Astherearepositivelyandnegativelychargedparticles,thereisacouplingbetweenthevariousequilibriainvolved16uponmixingtheparticles,whichshouldbeconsidered.•Finally,theSiO2NPscanbeconsideredasapolyionforwhichtheequilibriumalsoshouldbetakenintoaccount17,18.Alltheseaspectswillhavetobeincorporatedtorealisticallymodelnano-raspberryformation,butthisinevitablywillresultinacomplexmodel.

7SupplementaryTablesTableS1.CompositionofpHbuffersusedinthisstudyTargetpHMeasuredIngredientConcentrationVolumeIngredientBConcentrationVolumeIonicpHAofA(M)ofA(ml)ofB(M)ofB(ml)Strength(mM)21.6KCl0.150HCl0.11379.443.9Acetic0.1164CH3COO0.13672acidNa65.9KH2PO40.1100NaOH0.111.689.61212.4KCl0.150NaOH0.11280.6References(1)Israelachvili,J.N.IntermolecularandSurfaceForces.Elsevier,2011.(2)Russel,W.B.,Saville,D.A.,andSchowalter,W.ColloidalDispersions.CambridgeUniversityPress,Cambridge,UK,1989.(3)Overbeek,J.Th.G.StrongandWeakPointsintheInterpretationofColloidStability.Adv.ColloidInterfaceSci.1982,16(1),17–30.(4)Tuinier,R.ApproximateSolutionstothePoisson-BoltzmannEquationinSphericalandCylindricalGeometry.J.ColloidInterfaceSci.2003,258(1),45–49.(5)Sader,J.E.;Carnie,S.L.;Chan,D.Y.C.AccurateAnalyticFormulasfortheDouble-LayerInteractionbetweenSpheres.JournalofColloidAndInterfaceScience.1995,171,46–54.(6)Nguyen,A.V.,EncyclopediaofSurfaceandColloidScience;2012.(7)Elimelech,M.;Gregory,J.;Jia,X.;Williams,R.A.SurfaceInteractionPotentials.InParticleDepositionandAggregation;Elimelech,M.,Gregory,J.,Jia,X.,Williams,R.A.,Eds.;Butterworth-Heinemann,1995;pp33–67.(8)Bergström,L.HamakerConstantsofInorganicMaterials.Adv.ColloidInterfaceSci.1997,70,125–169.(9)Tsaur,S.-L.;Fitch,R.M.PreparationandPropertiesofPolystyreneModelColloids.J.ColloidInterfaceSci.1987,115,463–471.(10)Fowkes,F.M.AttractiveForcesatInterfaces.Ind.Eng.Chem.1964,56,40–52.(11)Lan,Y.;Caciagli,A.;Eiser,E.UnexpectedStabilityofAqueousDispersionsofRaspberry-likeColloids.Nat.Commun.9,(2018).(12)Carrière,D.;Belloni,L.;Demé,B.;Dubois,M.;Vautrin,C.;Meister,A.;Zemb,T.In-PlaneDistributioninMixturesofCationicandAnionicSurfactants.SoftMatter2009,5(24),4983–4990.(13)Andersson,Y.;Andersson,D.C.;Lundqvist,B.I.vanderWaalsInteractionsinDensity-FunctionalTheory.Phys.Rev.Lett.1996,76(1),102–105.(14)Israelachvili,J.;Wennerström,H.RoleofHydrationandWaterStructureinBiologicalandColloidalInteractions.Nature1996,379,219–225.(15)Marčelja,S.;Radić,N.RepulsionofInterfacesDuetoBoundaryWater.Chem.Phys.Lett.1976,42(1),129–130.(16)Netz,R.R.;Andelman,D.NeutralandChargedPolymersatInterfaces.Phys.Rep.2003,380(1–2),1–95.(17)Tamashiro,M.N.;Schiessel,H.WheretheLinearizedPoisson-BoltzmannCellModelFails:SpuriousPhaseSeparationinChargedColloidalSuspensions.J.Chem.Phys.2003,119(3),1855–1865.(18)Netz,R.R.;Orland,H.BeyondPoisson-Boltzmann:FluctuationEffectsandCorrelationFunctions.Eur.Phys.J.E2000,1(2–3),203–214.