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Listofcontributorsix
1.Self-healingpolymericsystems— fundamentals,stateofart,and challenges1
AnuSurendranandSabuThomas
1.1Introduction1
1.2Roleofnanofillersinself-healingpolymeric systems6
1.3Keydevelopmentsinthefieldofself-healing polymericsystems8
1.4Challengesforfabricatingself-healingmaterials basedonpolymericsystems11
1.5Conclusions13
References13
2.Typesofchemistriesinvolvedin self-healingpolymericsystems17
AnilK.PadhanandDebaprasadMandal
2.1Introduction:chemicalaspectsinself-healing process17
2.2Keyrequirementsofself-healingprocess18
2.3Dynamiccovalentnetworkinself-healing20
2.4ThermoreversibleDiels Alderandretro Diels Alderchemistry20
2.5Photoinducedself-healing: [2 1 2] cycloaddition 25
2.6Chemicaltransformationsinvolvedin self-healing26
2.7Reversiblecovalentreactioninvolvedin self-healing29
2.8Chemicaltransformationsthroughinvolved reactioninself-healing36
2.9Supramolecularnoncovalentinteraction39
2.10Chemistriesinvolvedinmicrocapsule-based self-healingpolymericsystem60
2.11Conclusions64
References65
3.Self-healingpolymers:fromgeneral basicstomechanisticaspects75
MartinD.HagerandStefanZechel
3.1Introduction75
3.2Generalmechanismofself-healing polymers76
3.3Conceptsforthedesignofself-healing polymers79
3.4Extrinsicself-healingpolymers79
3.5Intrinsicself-healingpolymers82
3.6Othermechanisticaspects89
3.7Conclusions90 References91
4.Shapememory-assistedself-healing polymersystems95
WenjingWu,JamesEkeocha,ChristopherEllingford, SreeniNarayanaKurupandChaoyingWan
4.1Introduction95
4.2Shapememoryandself-healing mechanisms96
4.3Shapememory-assistedself-healing107
4.4Applications116
4.5Conclusions118 References118
5.Characterizationofself-healing polymericmaterials123
SaiedNouriKhorasaniandRasoulEsmaeelyNeisiany
5.1Introduction123
5.2Methodsforevaluatingself-healing behaviorofthepolymericcomposites124
5.3Methodsforevaluatingself-healing behaviorofthepolymericcoatings129
5.4Summaryandoutlook135 References136
6.Roleofnanoparticlesinself-healingof polymericsystems141
JunfengSu
6.1Introduction141
6.2Self-healingpolymerusingmetal nanoparticles143
6.3Self-healingpolymerusinginorganic nanoparticles144
6.4Self-healingpolymerusingorganic nanoparticles148
6.5Furtheradvice162
References163
7.Self-healingbiomaterialsbasedon polymericsystems167
BaolinGuoandRuiYu
7.1Introduction167
7.2Self-healingbiomaterialsintissue engineering168
7.3Self-healingbiomaterialsindrug/genedelivery systems188
7.4Self-healingfunctionalsurfaces191
7.5Thecharacterizationofself-healing194
7.6Newopportunitiesandchallenges195
Acknowledgments200
References200
8.Self-healingDiels Alderengineered thermosets209
ZeinabKarami,MohsenZolghadrandMohammad JalalZohuriaan-Mehr
8.1Fundamentalsofself-healing209
8.2Typesofself-healingsystems210
8.3Diels Alderreaction210
8.4Diels Alder-basedhealablethermosets214
8.5Summaryandoutlook225
References227
9.Self-healingpolymericcoatings containingmicrocapsulesfilledwith activematerials235
S.MojtabaMirabediniandFarhadAlizadegan
9.1Introduction235
9.2Requirementsfordesigningaself-healing coating236
9.3Microcapsule-basedself-healingsystems237
9.4Microcapsulepreparationmethods245
9.5Materialsselectionforcoreandshell componentsofmicrocapsules248
9.6Limitationsandshortcomingsof microcapsule-embeddedcoatings252
9.7Summary253
References254
10.Capsule-basedself-healingpolymers andcomposites259
MariaKosarli,DimitriosBekas,KyriakiTsirkaand AlkiviadisS.Paipetis
10.1Introduction259
10.2Capsulesynthesisandcharacterization260
10.3Self-healingpolymersandcomposites267
10.4Self-healingcoatings273
10.5Conclusionsandfuturetrends274
References275
11.Ionomersasself-healing materials279
S.MojtabaMirabediniandFarhadAlizadegan
11.1Introduction279
11.2Materials,chemistry,andfundamentals280 11.3Theself-healingmechanisms283
11.4Activationmethods284
11.5Applications284
11.6Summary288
References288
12.Self-healingmaterialsutilizing supramolecularinteractions293
JamesF.Reuther,RandallA.Scanga,AliShahrokhinaand PriyankaBiswas
12.1Intrinsicself-healingsystems293
12.2Main-chainsupramolecularpolymers297
12.3Self-healingmaterialsdrivenbymetal coordination305
12.4Self-healingmediatedbyelectrostatic interactions322
12.5Host guestinteractionsinself-healing materials332
12.6Dynamiccovalentself-healingmaterials340
12.7Hydrogenbondinginself-healing systems351
12.8Conclusionsandfutureoutlook356 References356
13.Self-healinghydrogels369
ImtiazHussainandGuodongFu
13.1Introduction369
13.2Self-healing371
13.3Self-healinganditscharacterization371
13.4Chemistryinvolvedinintrinsic self-healing372
13.5Self-healingprocess378
13.6Classificationofself-healinghydrogels379
13.7Mechanismofself-healingofhydrogels381
13.8Factorsimpactonself-healing mechanism384
13.9Sacrificialbonds385
13.10Natureandmechanismsofsacrificial bonds385
13.11Inspiredsacrificialbondsinartificial polymericmaterials386
13.12Sacrificialbondsinhydrogels387
13.13Metal ligandpolymerhydrogels390
13.14Self-healinggelsmechanismbasedon constitutionaldynamicchemistry392
13.15Naturalpolymer-basedhydrogels392
13.16Recentdevelopmentinmiscellaneous applicationfields408 References413
14.Acontinuummechanicsapproachto thehealingefficiencyofextrinsic self-healingpolymers425
AmirShojaeiandGuoqiangLi
14.1Introduction425
14.2Finitedeformationkinematics:elastic,plastic, damage,andhealinginpolymers429
14.3Plasticdeformationinpolymers431
14.4Continuumdamageandhealing mechanics434
14.5Physicallyconsistentevolutionlawsforthe damageandhealingprocesses442
14.6Concludingremarks450 References451
15.Self-healingfiber-reinforcedpolymer compositesfortheirpotentialstructural applications455
NazrulIslamKhanandSudiptaHalder
15.1Introduction455
15.2Scopeofself-healinginfiber-reinforced polymercomposites456
15.3Extrinsicself-healingapproachesfor fiber-reinforcedpolymercomposites460
15.4Intrinsicself-healingapproachfor fiber-reinforcedpolymercomposites463
15.5ThermoreversiblehealingofFRP465
15.6Assessmentofself-healingefficiencyfor fiber-reinforcedpolymercomposites466
15.7Conclusions468
Acknowledgments468
References468
16.Self-healingpolymericcoatingfor corrosioninhibitionandfatigue repair473
VikasS.Hakke,UdayD.bagale,ShirishH.Sonawane, DipakPinjari,S.ManigandanandShriramSonawane
16.1Backgroundofself-healingandcorrosion inhibition473
16.2Self-healingandcorrosioninhibitor materials474
16.3Casestudyforself-healingmaterialand corrosioninhibitors478
16.4Polymercapsules-basedself-healingcoatingfor corrosioninhibition484
16.5Nanocontainer-basedself-healingapproachfor corrosioninhibition487
16.6Clay-basedself-healingmaterialsforcorrosion inhibition489 Conclusions490 References490
17.Applicationsofself-healingpolymeric systems495
JomonJoy,ElssaGeorge,S.AnasandSabuThomas
17.1Introduction495
17.2Applicationinwoundhealing496
17.3Applicationintissueengineering498
17.4Applicationinthree-dimensionalprinting499
17.5Applicationindrugdelivery500
17.6Applicationinanticorrosioncoating501
17.7Applicationinelectronicapplication503
17.8Applicationinaerospaceapplications506
17.9Conclusions508 References508
Index515
ListofContributors
FarhadAlizadegan IranPolymerand PetrochemicalInstitute,Tehran,Iran
S.Anas SchoolofChemicalSciences,Mahatma GandhiUniversity,Kottayam,India; AdvancedMolecularMaterialsResearch Centre,MahatmaGandhiUniversity, Kottayam,India
UdayD.bagale DepartmentofChemical Engineering,NationalInstituteof Technology,Warangal,India
DimitriosBekas StructuralIntegrityand HealthMonitoringGroup,Departmentof Aeronautics,ImperialCollegeLondon,South KensingtonCampus,London,United Kingdom
PriyankaBiswas DepartmentofChemistry, UniversityofMassachusettsLowell,MA, UnitedStates
JamesEkeocha InternationalInstitutefor NanocompositesManufacturing,University ofWarwick,Coventry,UnitedKingdom
ChristopherEllingford InternationalInstitute forNanocompositesManufacturing, UniversityofWarwick,Coventry,United Kingdom
GuodongFu SchoolofChemistryand ChemicalEngineeringSoutheastUniversity, Nanjing,P.R.China
ElssaGeorge SchoolofChemicalSciences, MahatmaGandhiUniversity,Kottayam, India
BaolinGuo FrontierInstituteofScienceand Technology,StateKeyLaboratoryfor MechanicalBehaviorofMaterials,Xi’an JiaotongUniversity,Xi’an,P.R.China
MartinD.Hager LaboratoryforOrganicand MacromolecularChemistry(IOMC), FriedrichSchillerUniversityJena,Jena,
Germany;JenaCenterforSoftMatter(JCSM), FriedrichSchillerUniversityJena,Jena, Germany
VikasS.Hakke DepartmentofChemical Engineering,NationalInstituteof Technology,Warangal,India
SudiptaHalder DepartmentofMechanical Engineering,NationalInstituteofTechnology Silchar,Silchar,India;DepartmentofCivil, ConstructionandEnvironmental Engineering,TheUniversityofAlabama Engineering,Tuscaloosa,AL,UnitedStates
ImtiazHussain SchoolofChemistryand ChemicalEngineeringSoutheastUniversity, Nanjing,P.R.China;CollegeofScience, NanjingForestryUniversity,Nanjing,P.R. China
JomonJoy SchoolofChemicalSciences, MahatmaGandhiUniversity,Kottayam, India
ZeinabKarami BiobasedMonomersand PolymersDivision,Adhesive&Resin Department,IranPolymerandPetrochemical Institute,Tehran,Iran
NazrulIslamKhan DepartmentofMechanical Engineering,NationalInstituteofTechnology Silchar,Silchar,India;Departmentof MechanicalEngineering,GMRIT,Srikakulam, India
SaiedNouriKhorasani Departmentof ChemicalEngineering,IsfahanUniversityof Technology,Isfahan,Iran
MariaKosarli DepartmentofMaterialsScience &Engineering,UniversityofIoannina, Ioannina,Greece
SreeniNarayanaKurup InternationalInstitute forNanocompositesManufacturing,University ofWarwick,Coventry,UnitedKingdom
GuoqiangLi DepartmentofMechanical Engineering,LouisianaStateUniversity, BatonRouge,LA,UnitedStates
DebaprasadMandal Departmentof Chemistry,IndianInstituteofTechnology Ropar,Rupnagar,India
S.Manigandan DepartmentofChemical Engineering,IndianInstituteofTechnology, Ropar,India
S.MojtabaMirabedini IranPolymerand PetrochemicalInstitute,Tehran,Iran
RasoulEsmaeelyNeisiany Departmentof MaterialsandPolymerEngineering,Faculty ofEngineering,HakimSabzevariUniversity, Sabzevar,Iran
AnilK.Padhan DepartmentofChemistry, IndianInstituteofTechnologyRopar, Rupnagar,India
AlkiviadisS.Paipetis Departmentof MaterialsScience&Engineering,University ofIoannina,Ioannina,Greece
DipakPinjari NationalCenterfor NanoscienceandNanotechnology,University ofMumbai,Mumbai,India
JamesF.Reuther DepartmentofChemistry, UniversityofMassachusettsLowell,MA, UnitedStates
RandallA.Scanga DepartmentofChemistry, UniversityofMassachusettsLowell,MA, UnitedStates
AliShahrokhina DepartmentofChemistry, UniversityofMassachusettsLowell,MA, UnitedStates
AmirShojaei VarianMedicalSystems,Palo Alto,CA,UnitedStates;Departmentof MechanicalEngineering,LouisianaState University,BatonRouge,LA,UnitedStates
ShirishH.Sonawane DepartmentofChemical Engineering,NationalInstituteof Technology,Warangal,India
ShriramSonawane DepartmentofChemical Engineering,VisvesvarayaNationalInstitute ofTechnology,Nagpur,India
JunfengSu DepartmentofPolymerScience, SchoolofMaterialScienceandEngineering, TianjinPolytechnicUniversity,Tianjin, P.R.China
AnuSurendran InternationalandInter UniversityCentreforNanoscienceand Nanotechnology,MahatmaGandhi University,Kottayam,India
SabuThomas SchoolofChemicalSciences, MahatmaGandhiUniversity,Kottayam, India;InternationalandInterUniversity CentreforNanoscienceandNanotechnology, MahatmaGandhiUniversity,Kottayam, India
KyriakiTsirka DepartmentofMaterials Science&Engineering,Universityof Ioannina,Ioannina,Greece
ChaoyingWan InternationalInstitutefor NanocompositesManufacturing,University ofWarwick,Coventry,UnitedKingdom
WenjingWu InternationalInstitutefor NanocompositesManufacturing,University ofWarwick,Coventry,UnitedKingdom; AerospaceResearchInstituteofMaterials& ProcessingTechnology,Beijing,P.R.China
RuiYu FrontierInstituteofScienceand Technology,StateKeyLaboratoryfor MechanicalBehaviorofMaterials,Xi’an JiaotongUniversity,Xi’an,P.R.China
StefanZechel LaboratoryforOrganicand MacromolecularChemistry(IOMC), FriedrichSchillerUniversityJena,Jena, Germany;JenaCenterforSoftMatter(JCSM), FriedrichSchillerUniversityJena,Jena, Germany
MohammadJalalZohuriaan-Mehr Biobased MonomersandPolymersDivision,Adhesive &ResinDepartment,IranPolymerand PetrochemicalInstitute,Tehran,Iran
MohsenZolghadr SchoolofChemistry, UniversityofTehran,Tehran,Iran
Self-healingpolymericsystems— fundamentals,stateofart,and challenges
AnuSurendran1 andSabuThomas1,2
1InternationalandInterUniversityCentreforNanoscienceandNanotechnology, MahatmaGandhiUniversity,Kottayam,India 2SchoolofChemicalSciences, MahatmaGandhiUniversity,Kottayam,India
1.1Introduction
Thepotentialapplicationsofthepolymericsystemsarefastadvancingintherecentyears invariousstructuralapplicationssuchasaerospace,defense,andconstructionindustries. Thedamagetriggeredbyvariousfactorssuchasmechanical,thermal,andchemicalfactors hasseriousimplicationsonthestructuralintegrity,performance,andlifespanofthematerial.Avisiblefailurecouldbeeasilydetected,whereasstructurallevelmicrocracksremained undetected.Asurgeinthepresentunderstandingofthemicrostructureandfailuremechanismhaseffectedinexploringstrategiesforaddressingthefatigueresponseofthematerial [1].Theprerequisiteforself-healingisthatdamagetriggersself-healingbygeneratinga mobilephasewhichcoversthedamagezonebyeitherphysicalorchemicalinteractions. Oneofthemilestoneswasthedevelopmentofsmartmaterialswherethe“damagecould automateahealingresponseinthematerial” [2].Thedamagerepaircostsarehigher,time consuming,andsometimesdifficulttomonitorifitoccursinthemicrostructurelevel.
Self-healingoccursbyeitherautonomicornonautonomicbasedonthetypeofresponse todamage.Autonomicresponsedoesnotrequireanyexternalstimuli;damageitselfinitiatesthehealingprocess.Nonautonomichealingrequiresanexternalstimulussuchaslight orheatforinitiationofself-healingprocess.Anotherwaytoexpresstheclassofselfhealingmaterialsisas“extrinsic”and“intrinsic”self-healingmaterials.Extrinsicselfhealingimpliestheencapsulationofmicro-ornanocapsulesintothematerialduringthe initialfabricationresultinginthehealing.Thehealingactionistriggeredbytheruptureof
thesecapsulesinthepathofcracks,causingthereleaseofhealingagentsontothecrack site.Intrinsicself-healingdoesnotrequireanyencapsulationofhealingagents.Itrather occursbythephysical/chemicalinteractionsestablishedbetweenthecrackinterfaces whichimparttheself-healingaction.
Theabilitytofunctionalizationhaspavedthewayforinducingself-healingproperty forpolymericsystems.Alsotheinherentpotentialtoaccommodatehealingagentsinthe apparentlylargervolumeofmacromolecularchainnetworkalsofacilitatestheeasinessto induceself-healingproperty.Suchself-healingmaterialsfindpotentialapplicationsin automobile,civil,andaerospaceapplications.Self-healingmaterialsmanagestoreducethe damagerepaircostandeconomicburdenenhancingthelifetimeandmaterialreliability. Thedemandsforsuchsmartermaterialsareboomingandhenceresearchersshowtremendousinterestinfabricatinganddesigningmaterialswithself-healingproperty.
1.1.1Extrinsicself-healinginpolymericsystems
Extrinsicself-healinghasbeenfacilitatedtopolymericmaterialsforrecoveringtheoriginalpropertiesofthematerialsatreasonablecostafterdamage.Extrinsicself-healing impliesonthreeapproachesbasedonmicro/nanocapsulesembedment,hollowfiber embedment,andmicrovascularsystem.Inmicroencapsulationtechnique,healingagentis embeddedorphaseseparatedwithinthematrixsothathealingoccurswithoutexternal intervention.Acatalystisalsoincorporatedintothematrix.Thecrackrupturesthemicro/ nanocapsulescausingthereleaseofhealingagentintothematrix.Thereleasedhealing agenttraversesinthematrixthroughthecapillaryaction,whichcomeintocontactwith thecatalystcausingpolymerizationandfurtherclearsthedamage.Thedisadvantageof thistechniqueisthatitcauseslimitedhealingactionduetothesmallamountofhealing agent.Thereforemultiplehealingactionsarenotpossiblewiththemicro/nanocapsules. Bondandcoworkersdemonstratedself-healingutilizingthehollowglassfiberswhichcontainshealingagent [3 5].Hollowglassfiberapproachencapsulatesmorehealingagent andalsocouldreinforcethematrixandmostlypreferredthanmicroencapsulatedselfhealingapproach.Bondetal. [4] observedapparentrestorationofcompressivestrengthin epoxyresin-bondedhollowglassfiber.Fiberswithlargediameterandincreasedhollow fractionhaveincrementaleffecttothestrengthdeterminedunderaxialcompressiveloading.About97%ofthemechanicalstrengthwasrestoredafterinvestigationofimpactpropertiesfollowedbyfour-pointbendflexuraltesting [3]. Fig.1.1[6] representstheschematic representationofself-healingviahollowfibers. Fig.1.2 representstherepresentationof self-healingbymicro/nanocapsules.Microvascularsystemmimicsthebiologicalvascular systeminplantsandanimalswithacontinuoussupplyofhealingagentthroughacentralizednetwork.Thecrack-induceddeliveryofhealantstothematerialfurnishesmultiple healingabilitiesandrestorestheproperties [7].Thecontinuousdeliveryofhealingagentin thethree-dimensionalmicrovascularsystemsopenedupnewavenuesforrepeatablehealing instructuralcomponents.Ofthethreeautonomichealingsystems,microvascularhealing systemsoftenhavehighestefficiency.
Self-healingusingmicrovascularinterpenetratingnetworkswasfabricatedinepoxy resinsviadualinkdepositionandverticalinkwriting [9].Healingefficiencyof50%was 2
One-part resin
Polymer matrix
Hollow fiber
Resin system
Hardener system
Hollow fiber
Resin system
Micro encapsulated hardener
Hollow fiber
FIGURE1.1 Schematicrepresentationofselfhealingbyhollowfibers [6].Source: Reprinted fromS.Bleay,C.Loader,V.Hawyes,L. Humberstone,P.Curtis,Asmartrepairsystemfor polymermatrixcomposites.Compos.PartAAppl. Sci.Manuf.32(2001)1767 1776.doi:10.1016/ S1359-835X(01)00020-3,Copyright(2001),withpermissionfromElsevier.
retainedevenafter30consecutivehealingcycles.Nancyetal. [10] developedtwosetsof independentvascularnetworks;onecomprisingofresinpartandothercomprisingof aminecuringagentwasembeddedinthepolymersubstratecoating.Thehealingcomponentsgotwickedundercapillaryactioninthedamagesiteandclosethecrackduetothe reactionoftheresinandcuringagent.Coaxialelectrospinningtechniqueswereutilizedfor incorporationoflinseedoil,aself-healingagentingrapheneoxide(GO)-reinforcedpolyacrylonitrile(PAN)shells [11].GOdecoratedPANfiberswereincorporatedintoPUcoatings.Whencrackforms,linseedoilwillbereleasedandwillreactwithoxygenandgets solidifiedcoveringthecrack.Moreover,GOhadimprovedthethermalstabilityofthe material.
1.1.2Intrinsicself-healinginpolymericsystems
Thisisaclassofnonautonomichealingsystemwhichrequiresexternalstimuliforselfhealing.Thisinvolveshealingprocessviabondruptureandbondreformationandcould beoperatedovermultipletimes.Chemicalreactionsandmolecularinteractionswhichcan beactivatedbyheat,light,electricalenergy,andmagnetismareexamplesforsuchsystems.Intrinsicself-healingisbasedonthepresenceofparticularreversiblechemical bonds.Since,intrinsicreversibilityofthesechemicalbondsenablesmultiplehealing responsesatthesamelocation.
ThermallyreversibleDiels Alder(DA)reactionsaremostwidelyusedforfabricating thermallyreversibleself-healingsystems.DAreactionrepresentstheclassof[4 1 2]cycloadditionreactionwhichoccursbetweenadieneandadienophile.Alkenesandalkynes attachedtoelectronwithdrawinggroupsaremostlyusedasadienophiletobringabout thereactionwithadiene.Furan maleimidechemistryismostlywidelyusedinthermally reversibleself-healingpolymericsystems.Petersonetal. [12] utilizedDAclickchemistry fordevelopingareversiblycross-linkgelasself-healingsiteintraditionalepoxy-amine reaction.Thehealingcouldberepeatedforaboutfivecyclesand21%ofthecomposite
FIGURE1.2 Schematicrepresentationofmicro/nanocapsule-embeddedself-healingsystems [8].Source: ReprintedfromM.Samadzadeh,S.H.Boura,M.Peikari,S.M.Kasiriha,A.Ashrafi,Areviewonself-healingcoatingsbased onmicro/nanocapsules.Prog.Org.Coat.68(2010)159 164.doi:10.1016/J.PORGCOAT.2010.01.006,Copyright(2010), withpermissionfromElsevier.
strengthwasrecoveredafterthefirsthealingcycle.Bowmanetal. [13] observedinterconversionsoffuranandmaleimideandobservedthatreversibleconversionsoccurredat74% at85 Cto24%at155 C,inacross-linkedpolymericsystem.Parketal. [14] fabricateda novelself-mendable bis-maleimidetetrafuran(2MEP4F),basedonDAreactionchemistry. Multipleself-healingafterelectricalresistiveheatingandshapememoryeffectswere observedforthesefunctionalcomposites.2MEP4Fpolymersrestoredmolecularstructure andretainedthesimilarorslightlyimprovedfractureresistancepropertiesbythermally reversibleDAandretro-DAchemistry [15].
Anthracene maleimideDAsystemwerealsostudiedbymanyresearchersforfabricatingthermallyreversibleself-healingsystems [16,17].Poly(ethyleneterephthalate)copolymerscontaininganthracenestructuralunitsaremodifiedbyDAreactionswith maleimideswasfoundtobethermallyreversibleat250 C [16].Syrettetal. [18] reported thesynthesisofnovelwell-definedlinearandstarmethylmethacrylatepolymersbearing anthracene maleimideDAadductswithintheirmacromolecularbackboneexhibitingselfhealingproperties.Anevaluationoftheirabilitytocleaveonheatingto200 Candto reformonslowcoolingbacktoambienttemperaturewasobserved.H1NMRspectra revealedtwonewsignalsat6.49and5.3ppm,notpreviouslyseeninthespectraofthe DApolymerswereobservedaftertheretro-DAprocess.Thereformedproductformed wasamixtureof endo and exo isomericDAlinkers.Thermallystableself-healingpolymer basedonDAreactionbetweenanthraceneandmaleimidewerefabricatedbyYoshieetal. [19].Here,self-healingwasaccomplishedatroomtemperaturebyDAadditionreaction andretroDAreversereactionwasinducedbymechanicalstress.Wangetal. [20] reported
theself-healingofpolyurethaneelastomerbasedonDAreactionbetweenfuranandbismaleimideendcappedgroupsandobtainedanefficiencyof81%aftertensilebreak recovery.
Thermoreversiblereactionsatthealkoxyaminejunctionalsoserveasamethodto induceself-healingpropertiesandrestorationofcracksinthepolymericchain.The dynamicequilibriumofC ONbondinalkoxyamineincorporatedepoxycuredwith diethylenetriamineenabledrestorationofimpactpropertieswhichwasstudiedbyRong etal. [21].ThereversibilityofC ONbondbreakageandreformationwasalsoenhanced byincorporationofSi Olinkagesintheepoxypolymericchains.Stiffpolyurethanepolymerwithself-healingpropertyutilizingalkoxyaminechemistrywasreportedbyZhang etal. [22].Thesematerialsexhibitedrepeatableself-healingpropertyatroomtemperature andexhibitedimpactfracturerecoveryatroomtemperature.
Thepolymericsystemswhichexhibitself-healingthroughreversiblehydrogenbondinginteractionhadbeenfabricatedsuccessfullybymanyresearchers [23 26] .Selfhealingrubberbyreversiblehydrogenbonds wasfabricatedatroomtemperaturewhich exhibitedlittlecreeponloadbyLiebleretal. [27] .Guadagnoetal. [28] reportedselfhealinginepoxy-MWCNTnanocompositesviareversiblehydrogenbonding.MWCNTs werecovalentlyfunctionalizedwithhydrog enbondingmoieties,suchasbarbiturateand thymine,andincorporatedintorubber-modifiedepoxynetworkestablishedreversible hydrogenbondedMWCNTbridgesacrossthematrix.Here,theyhaveachievedcharacteristicself-healingefficienciesranging formorethan50%.Hydrogelsfunctionalized withpoly(styrene-acrylicacid)core shellnanoparticlesbearingcarboxylgroupshaving self-healingpropertywasfabricatedbyHanetal. [29] .Enhancingmechanicalproperties togetherwithself-healingpropertyisachallengeinthecaseofelastomers.Huangetal. [30] fabricatedanovelself-healingelastomerwithhightensilestress(2.6MPa),high toughness(B14.7MJm 3),highstretchability( B1700%),andexcellentself-healingability(90%).Elastomerswithself-healingproper tyaredesirableforfabricationofflexible electronics.Theelastomerwassynthesiz edbyaone-potpolycondensationreaction between bis (3-aminopropyl)-terminatedpoly (dimethylsiloxane)(PDMS)and2,4 0 -tolylene diisocyanate.Thepreparedelastomerwasfi nallycoordinatedwithAl(III)ions.Both hydrogenbondsandcoordinationbondswereresponsibleforinducingself-healing propertytogetherwithenhancedmechanical property.Finallytheyweresuccessfulin demonstratingaflexibleelectr odewiththeirfabricatedPDMS TDI Alelastomerfilm (Fig.1.3).
Self-healingsystemsmanagedby π π stackinginteractionshavealsogainedattention recently.Supramolecularpolymericsystemsbasedon π π stackinginteractionswereused forimpartingthermoreversiblehealingbehavior.Self-healingofsupramolecularpolymeric systemsbasedonchainfoldingof π-electron-poorreceptorsitesofpolydiimidesitesand π-electron-richchainendsofthepolysiloxanewerereportedbyGreenlandetal. [31] Supramolecularpolymericsystemsbasedonblendofapyrenyl-tweezer-endedpolyamide intercalatingwithachain-foldingpolyimideshowedself-healingpropertyandenhanced toughnesswerereportedbyColquhounetal. [32].Anotherworkdonebythesamegroup [33] reportedbothhydrogenbondingandaromatic π π stackingbetweenthe π-electrondeficientdiimidegroupsandthe π-electron-richpyrenylunitswhichaccountedforselfhealingpropertyofsupramolecularpolymericsystems.
FIGURE1.3 (A)SEMimagesoftheAufilmelectrode.(B)Schematicdemonstrationofthestretchingprocess involvingtheflexibleelectrode.(C)Stress straincurvesofthepolymerfilmsforPDMS TDI Al-3(black),original(red),andhealingelectrode(blue).(D)Photographsofanotchedstrainelectrodeonrelaxedandstretching station.(E)Changeofrelativeresistanceoftheelectrodeunderdifferentstrains.(F)Durabilitytestofthestrain electrodeunderarepeatedstretchingandreleaseof40%.(G)Photographsoftheelectrodeonrelaxedandstretchingstation.(H)PhotographsofthehealingprocessfortheelectrodewithanLEDinserieswithaself-healingelectrode. PDMS,Polydimethylsiloxane.Source: ReprintedwithpermissionfromX.Wu,J.Wang,J.Huang,S.Yang, Robust,stretchable,andself-healablesupramolecularelastomerssynergisticallycross-linkedbyhydrogenbondsandcoordinationbonds.ACSAppl.Mater.Interfaces.11(2019)7387 7396.doi:10.1021/acsami.8b20303,Copyright(2019)American ChemicalSociety.
1.2Roleofnanofillersinself-healingpolymericsystems
Thenanofillersaidinimprovingtheself-healingefficiencyandmechanicalproperties inpolymericsystems.Itwillprovidebetterscratchresistanceandthermalstability. Nanofillersevencatalyzestheself-healingaction.Nanofillerssuchasgraphene,carbon nanotubes,nanosilica,andnanocellulosewereusuallyusedinself-healingpolymeric
systems.Synergesticperformanceofthematerialforvariousfunctionalapplicationsoften compromiseswiththemechanisticperformance.Thereforeimpartingself-healingfunctionsimprovestheoverallperformanceandlifetimeofthematerial.Theeaseoffunctionalizationofthenanofillersalsocouldcontrolthepolymer nanofillerinterfacial movement,interactionchemistriesforhealingaction,mechanicalpropertiesenhancement andstiffnessreinforcement.Usuallythecapsule-basedhealingsystemneedtocompromise withthetensileproperties.Wangetal. [34] demonstratedself-healingpropertiesof rubber MWCNTnanocompositesbasedonDAbonding.MWCNTactedasbothahealant andreinforcingagentinfurfuryl-graftedstyrene-butadienerubber(SBR).ThefurfurylgraftedSBRandfurfuryl-terminatedMWCNTwerereactedwithbifunctionalmaleimide toformDAadduct.Thenanocompositesexhibitedthermalhealingandhigherhealing efficiencywasobservedfornanocompositeswhichweresubjectedtolongerhealingtime andhigherhealingtemperature.Hanetal. [35] developedaconductingpolymerhydrogelsbasedonaviscoelasticpolyvinylalcohol(PVA) boraxgelmatrixandnanostructured cellulosenanofibers polypyrrole(CNFs PPy)complexes.CNFactedasabiotemplate andPPyimpartedconductivepropertytothehydrogels.CNF PPycomplexestanglewith thePVAthroughhydrogenbondingandalsoformreversiblecross-linkingwiththeborate ionsanchoredonthePVAchains.Thereversiblecross-linkingrenderstheself-healing property.
Kongparakuletal. [36] developedaself-healinganticorrosivecoatingbasedonepoxy nanosilicacomposites.Epoxyresinsembeddedwith3wt.%(3-glycidoxypropyl)trimethoxysilane-modifiednanosilicaand10wt.%perfluorooctyltriethoxysilane(POTS)microcapsulesdeliveredthebestanticorrosivepropertieswiththecorrosionrateof0.09mmyear 1 andoxygenpermeabilityabout0.14barrer.Theadditionofmodifiednanosilicaandselfhealingagentapparentlyincreasedthelengthofthediffusionpathwaysandthereby decreasedtheoxygenpermeabilityofthecoating.
Ranaandcoworkers [37] reportedagraphene-basedself-healingsystemwherethe nanofillershadcompensatedthereducedt ensilestrengthduetotheembeddedmicrocapsules.Apartfromthisthenanofillerhadalsoactedasacatalystforself-healing reactioninepoxy-basedsystems.Guadagnoetal. [28] developedanovelepoxynanocompositesexhibitingself-healingpropertiesbyreversiblehydrogenbonding.The functionalizationofMWCNTbyhydrogenbondinggroups,suchasbarbiturateand thymine,hadeffectedininducingself-healingproperty.Kongetal. [38] demonstrated EMIshieldingofFe 3 O 4 -loadedmultiwalledcarbonna notubes/polyazomethine(PAM) nanocomposites.Thesematerialsexhibitedexcellenthealingefficiencyof95%imparted bydynamiciminebonds.ApartfromtheEMIs hieldingeffectiveness,thesenanocompositescouldbedegradedondippinginanacidicsolutionfor30minatroomtemperatureandthedegradedproductscoulda gainbeusedforthesynthesisofthe nanocomposites.
Yuetal. [39] developedahydrogelhavingsuperiormechanicalandself-healingproperty.Hydrogelsexhibitingbothmechanicalstrengthandselfhealabilityarerare.They preparedanovelGO/poly(acryloyl-6-aminocaproicacid)compositehydrogelsexhibiting self-healingpropertyinresponsetopHstimulus.
Thedispersionofnanofillersstillremainsachallengeforresearchers.Theroleofnanofillersinself-healingpolymericsystemswillbedealtmoreinthefollowingchapters.
1.3Keydevelopmentsinthefieldofself-healingpolymericsystems
Researchonself-healingpolymer-basedmaterialswasquiteactivefromtheearly1900s. Withtheadventofinnovativetechniques,keyunderstandinginthefieldofmaterialsciencehasbeenincreased.Self-healingofpolymericsystemscouldbeinducedeitherautonomouslyornonautonomously.Apartfrominducingself-healingpropertieswithout compromisingotherpropertiesofthematerialsisachallengeforpracticalapplications. Self-healingmaterialsareextensivelyusedasstructuralcomponentssuchascoatings,biomedicalapplications,prosthetics,sensingapplications,medicalimplants,electricalapplications,andmembraneseparation.
Oneofthemostimportantapplicationsfortheself-healingpolymericmaterialswas usedforcorrosionprotection.Sunetal. [40] developedasuperhydrophobiccoating obtainedbylayer-by-layerassemblyofpoly(allylaminehydrochloride)andsulfonated poly(etherketone).Shchukinetal. [41] alsodemonstratedlayer-by-layerassembledpolymericcoatingsembeddedwithcorrosioninhibitorencapsulatedinnanocontainerforcorrosionprotection.ThecracksinducedpHchangeswhichreleasedthecorrosioninhibitor benzotriazole.
ParkandBraun [42] utilizedelectrospinningtechniqueforpolysiloxane-basedhealant encapsulationinanacrylatematrix.Here,healingagentswereencapsulatedintoabead onstringmorphologyandelectrospunontoapolymericsubstrate.Theadvantageofthis techniqueunderliesintheabilitytocontrolthesizeofmicrocapsulesandtherebythe releaseofhealingagents.
Polymericelectrolytescouldbeusedasalternativestoliquidelectrolytesforsolvingthe issueofelectrolyteleakageandinflammability.Theself-mendablepolymerelectrolytewill beabletoaddresstheissuesrelatedtoshortcircuitsandservicelifeofthebatterydueto crackformation.Xueetal. [43] hadfabricatedaflexible,highlystretchablepolymerelectrolytehavingself-mendingpropertyviaquadruplehydrogenbondingofureidopyrimidinone(UPy)moietiesinpolyethylenebackbone.Thepolyethyleneglycol(PEG)sidechains imparthighionicconductivity.Upymoietiesimpartphysicalcross-linksviahydrogen bondingresultedinhighlystretchableandflexibleelectrolyte.Apolymericelectrolyte withself-healingpropertywasdevelopedfordevelopinghighperformancelithiumion batteryusingSiO2.UPy-functionalizedSiO2 (SiO2-UPy)facilitatestheuniformdispersion ofSiO2 inthepolymermatrix,whichisessentialforfastconductionofLiions [44].Here, theself-healingpropertyisinducedbyformationofsupramolecularnetworkbetweenthe polymermatrixviaUPyonSiO2 andpolymermatrix.Quadruplehydrogenbondingis responsibleforself-healingproperty.Thepowertransmissioncablesrequiretheinsulating dielectricpolymerswhichneededtobeprotectedfromelectrictreeing.Wangetal. [45] usedPEG-functionalizedironoxide/polypropylenecompositeswhichexhibitedhealing propertyafterdamagedbyelectrictreeingalongwithrestorationofinsulatingproperties also.Polyelectrolytesbasedonpoly(acrylicacid)(PAA)cross-linkedbyhydrogenbonding havingsilicaparticlesexhibitthesamecapacitanceevenafter20cyclesofhealing [46].Pan etal. [47] reportedahydrogelelectrolytebasedonsodiumalginatecross-linkedby dynamiccatechol borateesterbonding.Themostimportantadvantageofthiselectrolyte isthatthehealabilityandcapacitancepropertiesweremaintainedbothatroomtemperatureandlowtemperature.
Parkandcoworkers [48] haddevelopedastretchableandself-healingenergystorage devicebasedonnickelflakes,eutecticgalliumindiumparticlesandcarboxylatedpolyurethane.Ithasexcellenthealingabilityandretains100%stretchabilityafterhealingand showsabout75%electricalhealingefficiency.Thethermallydrivenself-healingat80 Cis duetothereassociationofhydrogenbondsanchoredbycarboxylgrouponthePUsurface. Fig.1.4 representstheself-healingactionofthedevelopeddevice.Multifunctional materialswhichexhibitbothmechanicalself-healingandafunctionalpropertywhich makeitsuitableforrobustapplicationsareachallenge.Self-healingmaterialsexhibiting
FIGURE1.4 Self-healingactionofenergystoragedevicebasedonPU;(A)photosofthedeviceinoriginal, broken,andhealed,(B)GCDprofile,(C)capacityretentionatvariousbreaking/healingcycles,(D)GCDprofiles andcapacityretentionatdifferentstrainsofthedevicewithdifferentstrainsafterbreaking/healing,and(E) deviceunder0%,50%,and100%strainafterbreaking/healing [48] GCD,Galvanostaticchargedischarge.
sensingpropertiesandflexibilitycouldbeusedforsoftrobotics,prostheticsandother applications.Butintegratingbothfunctionsisachallengeforthescientists.Coeetal. [49] fabricatedamaterialbylayer-by-layerassemblyofcopper-cladpolyimidesheets,polyimidesheetsandanultraviolet(UV)-curableepoxy.TheUVcurableresinactedasastructuraladhesiveandself-healingcomponent.Polysiloxaneduetoitsstretchabilitywasused widelyforflexibleelectronicdevices.Jiangetal. [50] haddemonstratedapressuresensor onpolysiloxanecross-linkedwithDAhydrogenbonds.Theincorporationofgraphene nanosheetsimpartedhighmechanicalandelectricalproperties.Thefabricatedsensor undergoesasolid liquid solidtransformationduringself-healingprocess.ThefunctionalizationofPDMSwithfuranandmaleimideandfurtherpolymerizationprocessresulted inaDAproduct.ThethermalreversibilityofDAbondbreakingandformationresultedin self-healingofthepolysiloxaneelastomer.Zhangetal. [51] proposedanovelself-healing designbasedonpolyurethane/silvernanowiresforstrainsensingapplications.Theselfhealingwasinducedinsunlightforthematerialcausingtheexchangeoftheincluded disulfidebonds.Theadvantageofsunlightdrivenhealingisthatthematerialcouldbe usedforapplicationsrelatedtohumanbodysuchashuman machineinteractions,smart prosthetics,andwearablehealthmonitoringdevices.Xuetal. [52] developedaternary polymercompositecomprisingofpolyaniline,PAA,andphyticacidshowinghighstretchability(500%),excellentelectricalconductivity(0.12Scm 1),andself-healingproperties. Theself-healingisfurnishedbythehydrogenbondsandthecompositesishighlystrain andpressuresensitiveandhencecouldbeutilizedasstrainandpressuresensor.Zhang etal. [53] developedanovelself-healingstrainsensorbasedoncommerciallyavailable elastomersthroughasupramolecularassembly.Thesupramolecularhierarchicalnanostructureofcarbonnanotubeswasconstructedbyactivatedcellulosenanocrystalsthrough thermallyreversiblehydrogenbonds.Thesupramolecularassemblyofpolyethyleimine withcarboxyl-functionalizednitrilerubberwasshowingself-healingandexcellentelectricalandmechanicalproperties.
Environmentalpollutioncausedbyeitherhumaninterference/otherfactorsmaypollute thewaterbodiesandmayposeseriousthreattohealthoflivingbeings.Membraneseparationofwastewaterisanemergingtechniquetomeetthechallengesregardingpollution. Membraneseparationisfeasibleonlywhenthematerialcouldbeusedforlongterm.The costissuesforfabricationofmembranesarequitehigh.Luetal. [53] fabricatedamultiwalledcarbonnanotubefilmandpolydivinylbenzenewhichimpartssuperiorhydrophobicity.ThecoatingofPOTS(1H,1H,2H,2H-perfluorooctyltriethoxysilane)impartedselfhealingabilityforthisfilm.Theself-healingofthepolymer-coatedMWCNTfilmwas testedbyetchingthePOTSlayertoO2 plasma.Thissignificantlyreducedthefluorinecontentonthefilmsurface,butafter15minthecontentoffluorinewasrestored.Theyalso observedthedeteriorationofhydrophobicityjustaftertheO2 plasmatreatmentandthe restorationofhydrophobicityafter15min.Themechanismofself-healingisbasedonthe hydrolysisofPOTSinthepresenceofwaterandsubsequentcross-linkingtoformapolysiliconecompoundcausingrestorationofhydrophobicity.Themembraneshowedsuperior abilitytoseparatewater-in-oilemulsionsandoil/watermixtures.Afacileself-healing andsuperwettablenanofibrouspoly(ethylenimine)-poly(acrylicacid)/hyaluronicacid (bPEI-PAA/HA,namedPPH)membranewasfabricatedbyelectrospinningandlayer-bylayerapproachbyLuandcoworkers [54].ApurePANmembranewasfabricatedby
1.4Challengesforfabricatingself-healingmaterialsbasedonpolymericsystems
electrospinningtechnique,followedbydip-coatingofalayer-by-layerassemblyof bPEI-PAA/HA.Theself-healingabilitywasimmediatelyevidencedafter30sinthe presenceofwater.Theself-healingabilityisbroughtaboutbythehydrogenbonding. Whenacrackoccursandkeptincontactwithwater,thepolymershaveahighabilityto swellandfillthegapcausedbythedamage.
Polymericmembranesarewidelyusedinredoxflowbatteriesforseparationofcharge carriersinredoxactiveelectrolytes.Xuetal. [55] synthesizedablockcopolymerfrom vinylbenzylchlorideand2-((4-vinylbenzyloxy)methyl)furanbyRAFTpolymerization whichcouldbeusedasanionexchangemembranes.Theself-healingpropertywasincorporatedbytemperaturecontrolledDAreactionwhichhealedthecrackat150 C.Thematerialdeliveredastablecyclingperformanceover100consecutivecharge/dischargecycles, withaCoulombicefficiencyofmorethan97%andanenergyefficiencyof B79%.
Qinandcoworkers [56] hadfabricatedananisotropic,self-healinghydrogelswithmultiresponsiveactuatingability.Themetalnanostructureassembliescouldprovidedynamic interactionswiththepolymerswhichcouldbeutilizedforself-healingapplications.They proposedthiolate-silver(Ag)linkagesfromsilvernanoparticlesforfabricationoftough andself-healinghydrogels.Awatersolubledisulfideligand N,N-bis(acryloyl)cystamine (BACA)isusedformodifyingsilvernanoparticles.Ag@BACAnanocompositeswere obtainedbymixinginaqueousmediumatroomtemperature,resultinginthecleavageof S-Sbond.UndertheUVradiation,thesolvophobiceffectofsilvernanoparticlescaused theAg@BACAnanocompositesintergrateinto2Dlamellarassemblies.Thepolymerization ofAg@BACAwithpolyacrylamideresultedintheformationofAg/PAMlamellaeunder UVradiation.After30minofUVradiationexposure,SNPPhydrogelswereformedvia photothermalpolymerization.ThelargeamountofreversibleRS-AgsitescouldberegulatedinthepresenceoflightandpHstimulus.ThephotothermaleffectofAgnanoparticlesrenderedtheself-healingpropertyunderNIRlaser.TheaffinityofAgtoLewis protoninstrongacidsrenderedtheself-healingundertheeffectofpH. Fig.1.5 illustrates theself-healingperformanceofSNPPhydrogels.Theuniqueanisotropicstructuremade SNPPgelstoexhibitin-planeandout-of-planebendingactuations.Similarlygold-thiolate interactionswerealsousedasaself-healingmotifwithremarkablemechanicalproperties innanocompositehydrogels [57].
1.4Challengesforfabricatingself-healingmaterialsbasedonpolymericsystems
Therearealotofchallengesrelatedwiththefabricationofself-healingpolymericsystems.Thereliabilityofthematerialisdeterminedbytheefficiencytofullyundergoing healingandregainingtheoriginalproperties.Thereisanotherimportantparameterwhich affectstheself-healingpolymericsystems;regardingthecontinuityofhealinglife-cycleof polymericsystems.Thereisapparentlyanotherimportantparameterwhichshouldbe takencare;thatis,onthelocalizedresponseofself-healingaction.Intrinsicself-healing hadtackledtheproblemtosomeextent.Fortheeffectiveperformanceofthesmartmaterials,thesefactorsshouldbetakenintoaccount.Researchshouldbefocusedinthisaspect. So,moreworksshouldbedoneexploringthenovelself-healingchemistries,repeatedand localizedsupplyofhealingagentsinextrinsichealing,restorationofstrength,stiffness,
1.Self-healingpolymericsystems—fundamentals,stateofart,andchallenges
FIGURE1.5 Self-healingperformanceofSNPPhydrogels.(A)Illustrationofself-healingperformanceunderlaser andpH,(B)time temperatureplotofSNPPhydrogelsatdifferentpowersoflaseroutput,(C)stress straincurves ofSNPPhydrogelsfordifferenttimesofNIRlaserhealing,(D)UV visspectraofAg@BACArecordedtomonitor thebindingbehaviorbetweenBACAandsilverNPsindifferentpHsolutions,and(E)stress straincurvesofthe healedSNPPhydrogelpiecethroughapHmediatedway [56] BACA, N,N-bis(Acryloyl)cystamine; UV,ultraviolet.
toughness,andoverallperformanceofthematerial.Thestabilityofthematerials,performance,andself-healingactionshouldnotbeaffectedatambientconditions.Soresearch shouldbebasedonthesechallenges.
1.5Conclusions
Self-healinginpolymericsystemshasattractedattentionintherecentyears.Selfhealingsystemsmimicsthebiologicalsystems,oftheabilityofthecellularsystemstoheal byitself.Duetowideapplicabilityofpolymericsystemsinvariousapplications,methods toimproveitsstructuralintegrityandlifetimeareimportant.Thischapterdealswiththe fundamentalsofhealinginpolymericsystemsandthedifferenttypesofhealingsystems usedinpolymericsystems.Usuallyextrinsichealingsystemsisaccomplishedbythree approachesbasedonmicro/nanocapsulesembedment,hollowfiberembedment,and microvascularsystem.Itreliesonthefactthatnoexternalstimuliarerequiredforinitiationofself-healingaction.Although,thesesystemshavelimitedactionsincethehealing actionceasesoncethecatalystsareconsumed.Intrinsichealingsystemsrequireanexternal stimulus,whichisbasedonthereversiblechemicalinteractions.Theadventofnanotechnologyhasaidedinincreasingtheself-healingactiontogetherwithimprovingthestiffness ofthematerial.Apparentlymultiresponsivesmartpolymerswerefabricatedwhichwill self-healbasedonthespecificchemicalinteractionsinresponsetodifferentstimuli.More insightsintothechemistriesresponsibleforself-healingactionneedtobeexplored.This willimprovethelifetimeandperformanceofsoftmaterialswhichcouldbeutilizedina widerangeofapplicationssuchascoatings,polymericmembranesforwaterpurification, smartprosthetics,andhealthmonitoringdevices.
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