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1、ViewOnline/JournalHomepage/TableofContentsforthisissueREVIEWwww.rsc.org/softmatter
2、SoftMatterWhyaredoublenetworkhydrogelssotough?JianPingGong*Received18thNovember2009,Accepted9thFebruary2010FirstpublishedasanAdvanceArticleontheweb9thMarch2010DOI:10.1039/b924290bDouble-network(DN)gelshavedrawnmu
3、chattentionasaninnovativematerialhavingbothhighwatercontent(ca.90wt%)andhighmechanicalstrengthandtoughness.DNgelsarecharacterizedbyaspecialnetworkstructureconsistingoftwotypesofpolymercomponentswithoppositephysicalnatures:theminorcomponentisabundantlycross-linkedpolyelectrolytes(rigidskeleton)a
4、ndthemajorcomponentcomprisesofpoorlycross-linkedneutralpolymers(ductilesubstance).Theformerandthelattercomponentsarereferredtoasthefirstnetworkandthesecondnetwork,respectively,sincethesynthesisshouldbedoneinthisordertorealizehighmechanicalstrength.ForDNgelssynthesizedundersuitableconditions(choi
5、ceofpolymers,feedcompositions,atmosphereforreaction,etc.),theypossesshardness(elasticmodulusof0.11.0MPa),strength(failuretensilenominalstress110MPa,strain10002000%;failurecompressivenominalstress2060MPa,strain9095%),andtoughness(tearingfractureenergyof1001000Jm2).Theseexcellentmechanicalperfo
6、rmancesarecomparabletothatofrubbersandsoftload-bearingbio-tissues.ThemechanicalbehaviorsofDNgelsareinconsistentwithgeneralmechanismsthatenhancethetoughnessofsoftpolymericmaterials.Thus,DNgelspresentaninterestingandchallengingprobleminpolymermechanics.Extensiveexperimentalandtheoreticalstudiesha
7、veshownthatthetougheningofDNgelisbasedonalocalyieldingmechanism,whichhassomecommonfeatureswithotherbrittleandductilenano-compositematerials,suchasbonesanddentins.I.Introductionfriction(cartilage),androbustcontraction(muscle).1Thesesofttissues,containing3080%water,areexcellentsoft&wetBesidesbone
8、s,tooth,andnails,humanbodyconsistsofsoftmaterials.Seekingartificialsofttissuestosubstitutedamagedtissues,suchastendonsandligaments(fixingtheboneskeleton),realoneshasbeenachallengingtaskformaterialscientists.cartilage(adsorbingthesho
