表面活性劑膠束形狀隨濃度轉(zhuǎn)變的核磁共振研究_英文_

1、物理化學(xué)學(xué)報(WuliHuaxueXuebao)表面活性劑膠束形狀隨濃度轉(zhuǎn)變的核磁共振研究盧星宇1,2蔣艷1,2崔曉紅1,2毛詩珍1,*2劉買利1,*杜有如1(1中國科學(xué)院武漢物理與數(shù)學(xué)研究所,波譜與原子分子國家重點(diǎn)實(shí)驗(yàn)室,武漢430071;中國科學(xué)院研究生院,北京100049)摘要：運(yùn)用核磁共振一維氫譜和自擴(kuò)散實(shí)驗(yàn)方法研究了聚乙烯乙二醇異辛酚醚(TX-100)、十二烷基苯磺酸鈉(SDBS)和十四烷基三甲基溴化銨(TTAB)三種不同類型的表面活性劑在重水溶液中的膠束形狀轉(zhuǎn)變,發(fā)現(xiàn)它們在臨界膠束濃度以上的各自相應(yīng)濃度都有膠束形狀的變化(由球狀轉(zhuǎn)變?yōu)闄E球狀或棒狀).在常溫常壓和沒有其他添加劑的情況

2、下,表面活性劑溶液濃度高于其臨界膠束濃度時,球狀膠束開始形成.核磁共振一維氫譜和自擴(kuò)散實(shí)驗(yàn)的結(jié)果顯示,當(dāng)溶液濃度繼續(xù)增加到一定程度時,溶液中表面活性劑分子的化學(xué)位移和自擴(kuò)散系數(shù)的變化速率都有明顯的轉(zhuǎn)折,這說明溶液中球狀膠束開始發(fā)生轉(zhuǎn)變.進(jìn)一步通過仔細(xì)分析對比核磁共振一維氫譜中各基團(tuán)譜峰,發(fā)現(xiàn)表面活性劑膠束親水表面上的質(zhì)子的化學(xué)位移變化速率要遠(yuǎn)高于其疏水內(nèi)核中的質(zhì)子,據(jù)此推測膠束形狀很可能由球狀轉(zhuǎn)變?yōu)闄E球狀或棒狀.關(guān)鍵詞：表面活性劑;中圖分類號：O647核磁共振;膠束形狀轉(zhuǎn)變;第二臨界膠束濃度NMRStudyofSurfactantMicelleShapeTransformationwithCo

3、ncentrationLUXing-Yu1,2JIANGYan1,2CUIXiao-Hong1,2MAOShi-Zhen1,*LIUMai-Li1,*DUYou-Ru1(1StateKeyLaboratoryofMagneticResonanceandAtomicandMolecularPhysics,WuhanInstituteofPhysicsandMathematics,Abstract：Themicelleshapetransformationoftert-octylphenyphenolpolyethyleneglycolether(TX-100),sodiumdodecylbenz

4、enesulfonate(SDBS)andtetradecyltrimethylammoniumbromide(TTAB)inheavywatersolutionswasstudiedby1Hnuclearmagneticresonance(NMR)spectroscopy,includinganNMRself-diffusionexperiment.Theseexperimentsshowedthatthesurfactantsformedseveralshapesofmicelles(spherical,ellipsoidal,androdlike)attherespectiveconce

5、ntrationswhichwerefarabovetheircriticalmicelleconcentration(cmc).Atambienttemperature,normalpressureandwhentheconcentrationofthesurfactantwasabovethecmcwithoutotheradditives,sphericalmicelleswereformed.Athighersurfactantconcentrations,1HNMRspectraandself-diffusionexperimentsshowedthatabruptchangesoc

6、curredintheirchemicalshifts()andintheirself-diffusioncoefficients(D).Thisindicatedthatsphericalmicellestransformedintolargermicelles.Bycarefulexaminationofeveryprotonresonancepeakinthe1HNMRspectra,wefoundthattheprotonsneartheheadgroupexperiencedlargerchemicalshiftchangesthanprotonsnearthehydrophobic

7、group.Thissuggeststhattheshapeofsurfactantmicellesmostlikelytransformsfromsphericaltoellipsoidalorrodlike.KeyWords：Surfactant;NMR;Micelleshapetransformation;criticalmicelleconcentrationIIAsthemostbasalandordinaryformoforganizedsurfactantTheprojectwassupportedbytheNationalNaturalScienceFoundationofCh

8、ina(20610104,20635040).國家自然科學(xué)基金(20610104,20635040)資助項(xiàng)目鬁EditorialofficeofActaPhysico-ChimicaSinica1358ActaPhys.-Chim.Sin.,2009Vol.25shapesinthecomplexsolution,whichexhibitsvariousapplica-tionsinsimulationofbiomembrane,preparationofnanoparti-cles,andotherindustrialandtechnologicalprocesses1-4.Thema-jo

9、rfactorsthataffecttheshapeofmicellesarethenatureofthepolargroup,thelengthandthestructureofthehydrophobicchain,theadditivesuchaselectrolyteorpolarorganiccom-pound,thetemperature,andtheconcentrationofsurfactantinaqueoussolution5,6.Althoughnumerousstudiesofmicellizationhaveappearedintheliteratureandthe

10、grosscharacteristicsofmicellarcatalysisofvariouschemicalprocesseshavebeende-scribed6,relativelyfewstudieshavebeenconductedinwhichthemajoremphasiscenteredonthesizeandshapeofmicelles.Typically,ionicsurfactantsformsphericalmicellesinaqueoussolution,inwhichthehydrophobicinteractionofthehydrocar-bontailw

11、ouldbalancetheelectrostaticrepulsionsbetweenthechargedheadsatthemicellesurface.Ithasbeenshown7,8thattheadditionofsaltscreenstheseelectrostaticrepulsions,allowingthechargedsphericalmicellestogrowintoelongated,rodlikestructures.This“sphere-to-rod”transformationhasbeenwelldoc-umentedinthecaseofsodiumdo

12、decylsulfatemicelles7-9.Micellesizeandshapemayalsoshowabruptchangeswhensurfactantconcentrationsincreasetovalueshigherthanthecmc,whichissometimescalledthecmcII,evenintheabsenceofotheraddi-tives10-13.Theincreaseofsurfactantmoleculesinunitvolumemakesitpossibleforthemtoapproacheachothermorecloselyandfor

13、mlargeraggregates,whichrequiresmuchmorespaceforthehydrophobicchains.Becauseasphericalmicellehasasmallervolume,itpreferschangingtolarger,mostlikelyellip-soidalorrodlikemicelletoincreasethevolume/surfaceratio.Theexistenceofellipsoidalorrodlikemicelleswasinferredfromexperimentsoflightscattering14-16and

14、confirmedbydirectobservationundertheCryo-TEM17-19forsomesystems.Howev-er,evidencefortheexistenceofmanyothersurfactantellip-soidalorrodlikemicellesisnotverystrong.2ResultsanddiscussionChemicalstructuresandprotonnumberingofthethreesur-factantsstudiedareshowninScheme1.Fromthe1HNMRspec-tra,themajorinfor

15、mationweobtainedisthechemicalshift,whichissensitivetotheelectronicenvironment.Sinceneigh-boringmoleculescontributetotheelectronicstructure,NMRissensitivetothesolventenvironmentofamolecule.This“sol-venteffect”providesmolecularinformation.Inaqueoussolu-tions,themotionalbehaviorofthesurfactantmolecules

16、dependsonnotonlywhethertheyexistasmonomersormicelles,butalsothesizeofthemicelles.Meanwhile,asimilarargumentcanbemadeforself-diffusioncoefficientsofthesurfactantmolecules.Becausethetransla-tionalmobilitiesaregreatlyaffectedbyassociationphenomena,theobservedself-diffusioncoefficientsofthesurfactantmol

17、ec-ulescanbeofconsiderablehelpinthedeterminationofsolutionstructure.Insurfactant-watersystems,thereisalwaysafinitemonomerconcentrationandthesemonomerscancontributesig-nificantlytotheobservedaveragediffusion.Sincetheexchangeoftheindividualsurfactantmoleculesbetweenmonomersandmicellesisusuallyfast(the

18、inverseofthedifferenceinthecorrespondingresonancefrequenciesistypical-lyintheorderoforbelow10-3s),theNMRchemicalshifts(orself-diffusioncoefficients)foramicellarsystemcanbewrittenasapopulation-weightedaverage21,22,Aobs=AmicPmic+Amon(1-Pmic)(1)inwhich,AobsistheNMRobservedvalueofchemicalshifts(or1Exper

19、imentalTX-100(molecularweight(MW)=646.9)waspurchasedfromScheme1ChemicalstructuresandprotonnumberingofthethreestudiedsurfactantsNo.7LUXing-Yuetal.:NMRStudyofSurfactantMicelleShapeTransformationwithConcentration1359self-diffusioncoefficients);AmonandAmicarethemonomericandmicellizedchemicalshifts(orsel

20、f-diffusioncoefficients),respec-tively;Pmicisthefractionalpopulationofthemicellizedsurfac-tants.Ifitisassumedthattheconcentrationofmonomersisaconstantandequaltothecmc,Eq.(1)canbeexpressedasAobs=AmicPmic+Amon(1-Pmic)=(Amic-Amon)Pmic+AmonL-1abruptchangesatthesameconcentration,about2.85mmol·Fig.2V

21、ariationsoftheself-diffusioncoefficientandthemethylproton(H1)chemicalshiftversusreciprocalofconcentrationforTX-100Thedataonlinesrepresenttheslopesoffoursegments.Fig.1Variationofthemethylproton(H1)chemicalshiftversusreciprocalofconcentrationforTX-100Fig.3Variationofthemethylproton(H1)chemicalshiftver

22、susreciprocalofconcentrationforTX-100inalargerconcentrationrangefrom0.5to30mmol·L-11360ActaPhys.-Chim.Sin.,2009Vol.25Fig.4Variationsoftheself-diffusioncoefficientandthemethylproton(H1)chemicalshiftversusreciprocalofconcentrationforSDBSThedataonlinesrepresenttheslopesoffoursegments.Aobs=Amic1Pmi

23、c1+AmicNPmicN+Amon(1-Pmic1-PmicN)(4)NMRexperimentsofSDBS(Fig.4)andTTABatvariouscon-centrationsinD2Oat25alsoshowsimilarphenomenatothoseofTX-100.WhentheconcentrationofSDBSsolutionis12mmol·L-1(cmc=1.2mmol·L-123)andthatofTTABis26mmol·L-1(cmc=2.2mmol·L-123),thecurvesofboththechemicals

24、hiftandtheself-diffusioncoefficientplottedagainsttherecip-rocalconcentrationcometoaturn.Thentherearesimilarinfer-encestothoseforTX-100:sphericalmicellesofSDBSandTTABcouldtransformtolargeronesaround12mmol·L-1and26mmol·L-1,respectively.Accordingtoknownstudiesonthesurfactantmicelleusingotherm

25、ethods14-19,wecansupposethatellipsoidalorrodlikemicelleswouldbethemajorstateinsurfactantsolutionwhentheconcentrationismuchhigherthanthecmc.However,evidencefortheexistenceofthesethreesurfactantellipsoidalorrodlikemicellesisnotverystrong.Withfurtherexaminationofeveryprotonresonancein1HNMRspectraofthet

26、hreesurfactantsstudied,wecandiscussdynamicsituationsofthetransformationofsurfactantmicelles.Inthe1HNMRspectraofTX-100,wefindthatnotonlythe·whenthesurfactantconcentrationbecomeshigherthan26mmol-1L,whichindicatesthatthechemicalenvironmentaroundhy-drophobicchainsissteady.Thislikelyindicatesanother

27、kindoftransformationasshowninScheme2(b).Rodlikemicelleshaveasteadycore,thuswhenthesurfactantconcentrationincreaseson-lythelengthofthemicelleincreases,whichhardlychangestheFig.5Variationsofprotonchemicalshiftsofhydrophilic(H6)andhydrophobic(H1)groupsversusreciprocalofconcentrationforTX-100Thedataonli

28、nesrepresenttheslopesoffoursegments.Scheme2MicelletransformationfromsphericaltoellipsoidalorrodlikeNo.7LUXing-Yuetal.:NMRStudyofSurfactantMicelleShapeTransformationwithConcentration1361majormicellestate,monomers,sphericalmicellesandquasi-sphericalmicellesco-existinthesolution,untilthesurfactantconce

29、ntrationishighenoughforthemicellestoformlyotropicliquidcrystals.ReferencesFig.6Variationsofprotonchemicalshiftsofthehydrophilic(H5)andhydrophobic(H1)groupsversusreciprocalofconcentrationforTTABThedataonlinesrepresenttheslopesoffoursegments.45:295346:10016Isaac,L.;Mireille,A.;Marcelo,D.S.;Sergei,S.S.

30、;Michael,R.Macromolecules,2004,37:50021995,115:26022Groth,C.;Nyden,M.;Holmberg,K.;Kanicky,J.R.;Shah,D.O.J.SurfactantsDeterg.,2004,7:247andapplicationofmicelles,microemulsions,monolayers,bilayers,vesicles,host-guestsystemsandpolyions.NewYork:JohnWiley&Sons,Inc.,198224Jiang,Y.;Chen,H.;Cui,X.H.;Mao

31、,S.Z.;Liu,M.L.;Luo,P.Y.;25Cui,X.H.;Mao,S.Z.;Liu,M.L.;Yuan,H.Z.;Du,Y.R.Langmuir,2008,24:10771innerchemicalenvironment.ThisformationofrodlikemicellesislikelybecausetheTTABmoleculehasasmallerhydrophilicheadcomparedwithTX-100andSDBS,andthustheseTTABmoleculespreferarrangingsidebyside.Addinginorganicelec-

32、trolytetoanaqueoussolutionofsurfactantswhosehydrophilicheadisbiggerthanthehydrophobictailwouldalsoleadtotheformationofrodlikemicelles.3ConclusionsThemicelletransformationofthreesurfactantsinaqueoussolutionhasbeeninvestigatedby1HNMRspectraandNMRself-diffusionexperiments.Changesinchemicalshiftsin1HNMRspectraandthevariationofself-diff