Effectofsurfactantonporosity

ColloidsandSurfacesB:Biointerfaces88(2011)279–286ContentslistsavailableatScienceDirectColloidsandSurfacesB:Biointerfacesjournalhomepage:(sodiumacrylate-co-styrene)/attapulgitesuperabsorbenthydrogelsXiao-NingShia,b,Wen-BoWanga,c,Ai-QinWanga,c,∗aKeyLaboratoryofChemistryofNorthwesternPlantResources,LanzhouInstituteofChemicalPhysics,ChineseAcademyofSciences,Lanzhou730000,PRChinabGraduateUniversityoftheChineseAcademyofSciences,Beijing100049,PRChinacR&DCenterofXuyiAttapulgiteAppliedTechnology,LanzhouInstituteofChemicalPhysics,ChineseAcademyofScience,Huai’an223003,PRChinaarticleinfoArticlehistory:Received23January2011Receivedinrevisedform17June2011Accepted4July2011Availableonline12July2011Keywords:SurfactantPorosityGuargumHydrogelSwellingbehaviorabstractNovelfast-swellingporousguargum-g-poly(sodiumacrylate-co-styrene)/attapulgite(GG-g-P(NaA-co-St)/APT)superabsorbenthydrogelswerepreparedbysimultaneousfree-radicalgraftcopolymerizationreactionofguargum(GG),partiallyneutralizedAA(NaA),styrene(St)andattapulgite(APT)usingN,N-methylenebisacrylamide(MBA)asacrosslinkerandammoniumpersulfate(APS)asaninitiatorinaqueoussolutionandthesurfactantself-assemblingtemplatingpore-formingtechnique.Fouriertrans-forminfrared(FTIR)spectroscopyconfirmedthatthesurfactantcouldberemovedfromthefinalhydrogelproductbymethanol/water(8:1,v/v)washingprocessandthesurfactantonlyactasmicelletemplatetoformpores.Theeffectofsurfactanttypeontheporousmicrostructureofthehydrogelwasassessedbyfieldemissionscanningelectronmicroscope(FESEM).Itwasshownthatincorporationofproperamountofanionicsurfactantsodiumn-dodecylsulfate(SDS)inthegellingprocessofthehydrogelcanobviouslyenhancetheswellingcapacityandinitialswellingrate.Thesalt-sensitivityoftheSDS-addedhydrogelindistilledwaterand15mmol/LNaCl,CaCl2solutionor15mmol/LNaClandCaCl2solutionwasinvesti-gated,anditwasfoundthattheswelling–deswellingcapabilityisquitereversible.Asimilarreproducibleon–offswitchingbehaviorwasobservedinthe1mmol/LsolutionofphosphatebufferatpH2.1and7.4.©2011ElsevierB.V.Allrightsreserved.1.IntroductionSuperabsorbenthydrogelsareslightlycross-linkedthree-dimensionalhydrophilicpolymersthatarecapableofabsorbinglargequantitiesofwaterorotherbiologicalfluidswithoutdis-integrating,andhavefoundextensiveapplicationsinvariousareassuchasmedicine/pharmacy[1–3],chemicalengineering[4–6],agriculture[7–9]andotherenvironmentalfields[10–12].Inthedesignanddevelopmentofnewsuperabsorbenthydrogels,highswellingcapacity,fastswellingrateandgoodgelstrengthwereespeciallydesired.Amongtheseproperties,swellingrateisimportantbecauseitdeterminestheapplicationpropertiesofsuperabsorbenthydrogelinalmosteachfield.Recently,manyeffortshavebeenmadetoimprovetheswellingrateofthesuper-absorbenthydrogelforimprovingitsapplicability[13–16].Inprinciple,theinitialswellingrateofasuperabsorbentisprimar-ilyduetothepenetrationofwatermoleculesintothepolymericnetworkthroughdiffusionandcapillarity[17].Higherporosityin∗Correspondingauthorat:KeyLaboratoryofChemistryofNorthwesternPlantResources,LanzhouInstituteofChemicalPhysics,ChineseAcademyofSciences,Lanzhou730000,PRChina.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](A.-Q.Wang).thesuperabsorbentscanincreasethecontactareabetweenpoly-mericnetworkandexternalsolutionthatfacilitatetospeedupthediffusionrate[15].So,theswellingrateofsuperabsorbenthydrogelscanbeenhancedthroughthecreationofporositystruc-ture.Variousmethods,suchasthephaseinversiontechnique[18],freeze-dryingandhydrationtechnique[19],thewater-solubleporogens[20]andthefoamtechnique[21,22],havebeenusedtocreatetheporousstructureofhydrogels.However,thecontra-dictionbetweenthecontrollableporosityandtheconvenienceofthepore-formingtechniqueisnowstillexistinginthehydrogelpolymerization.Surfactantcanself-assembletoformmicellesinaqueousenvi-ronment,whichactasatemplateinthepolymerizationreactionprocesstoproducepores[23].Akindofporousalginatehydrogelsthatporesizecanbecontrolledbyvaryingthesurfactantconcen-trationhasbeendeveloped[24].Inaddition,thegelationofaqueoussolutionofcellulosederivativesandsurfactantsisalsostudiedbySuetal.[25].Theresultanthydrogelholdsmuchmicroporewithinitsnetworkstructureandcanbewidelyappliedinpharma-ceuticals,cosmeticsandfoodindustry[26,27].Otherresearchershaveextendedthesurfactanttodevelopchitosan-basedhydro-gelforenhancingitsadsorptioncapacityonthewastedyeandotherorganiccompounds,andthisapproachiseconomicalandtechnicallyfeasible[28–30,15].Thus,itisexpectedthattheporous0927-7765/$–seefrontmatter©2011ElsevierB.V.Allrightsreserved.doi:10.1016/j.colsurfb.2011.07.002280X.-N.Shietal./ColloidsandSurfacesB:Biointerfaces88(2011)279–286structureandswellingpropertiesofahydrogelcouldbeimprovedbyintroducingsurfactant.Inresponsetothefullypetroleum-basedpolymerswithseri-ousenvironmentimpact,polysaccharide-basedhydrogelshaveattractedmuchattentionduetotheirrenewable,biocompatibleandbiodegradableadvantages.Polysaccharidessuchasstarch,chito