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1、NanoscaleROYALSOCIETYOFCHEMlSTRYPAPERViewArticleOnlineV沁WJournalVieuIssue册CheckforupdatesCitethis:Nanoscale,2020,12,16562WearableelectronicsforheatingandsensingbasedonamultifunctionalPET/silvernanowire/PDMSyarn+.5 Y b/8。N WULW co 人=已。Acn enuo,q POPEO300 OZOZAsf 6Z u。pws=qndZhonglin Yang,* Wenwen Wan
2、g,* Lili Bif Liangjun Chen, Guixin Wang, Guinan Chen, Cui Ye * and Jun Pan tStretchable and fl eible electronics built from multifunctional fi bres are essential for devices in humanmachine interactions, human motion monitoring and personal healthcare. However, the combination of stable heating and
3、precision sensing in a single conducting yarn has yet to be achieved. Herein, a yarn comprising poly(ethylene terephthalate) (PET), silver nano wires (AgNWs), and polydimethylsiloxane (PDMS) was designed and prepared. The PET/AgNW/PDMS yarn exhibited high electrical conductivity at 3 cm-1 and a larg
4、e tolerance to tensile strain up to 100% its own length. Only a negligible loss of electromechanical performance was observed after 1700 strain cycles. And an excellent response to applied strain was also achieved across a huge stretching range. The PET/AgNW/PDMS yarn displayed excellent heating per
5、formance and outstanding breathability when used in a heating fabric, and excellent sensitivity for monitoring both gross and fi ne movements in humans when used as a sensor.Received26thMay2020,Accepted29thJuly2020DOI:10.1039d0nr04023arsc.li/nanoscaleIntroductionFlexibleandstretchablematerialsareatt
6、ractiveforuseinartificialskin,orforbuildingdevicesusedindevelopinghumanmachineinteractions,monitoringhumanmotion,andpersonalhealthcare.-Electricallyconductingyarnshavebeenshowntodisplayremarkableperformancesinenergystorage,sensing,actuation,andCommUniCation.-12Recently,nanomaterialswithexcellentelec
7、tricalandmechanicalproperties,suchascarbonnanotubes,u,i4metalnanowires,is-uandgraphene,havebeenusedtodevelopelectricallyconductingyarns,butsilvernanowires(AgNWs)haveshownthemostpromisebecauseoftheirexcellentconductivityandstretchability.19-22Additionally,variousmethodsareappliedtofabricateAgNWsbased
8、conductingyarnsuchasspraycoating,dip-coating,laserscribing,andSPin-COating.23-26Amongthem,themostsimpleandcheapapproachistodepositAgNWsontoayarnsubstrate.Forpreparingcomfortableandeffectivedevicesfortrackinghumanmovementorprolongedstableheating;thewearableelectronicmustbebreathable,flexibleandstretc
9、hable.27-29MechanicaldeformationsuchasstretchingandbendingCollegeofMaterialsScienceandEngineering,ZhejiangUniversityofTechnology,Hangzhou310014,China.E-mail:panjun0123.ye0702tElectronicsupplementaryinformation(ESI)available.SeeDOI:10.1039/d0nr04023a，Equalcontributiontothisworkusuallydestroystheconne
10、ctivitybetweenconductingfibres,whichinitiallycausesinconsistenciesintheelectricalresistance(referredtoasresistance)throughoutthefabric,buteventuallyleadstodevicefailure.Long-termstabilityisthereforeanessentialresearchgoalfornewconductingyarns.Chengetal.developedaconductingfibrewithahierarchicalEcofl
11、ex-coatedcoppernanowire(CuNW)structure,whichwasusedinstable,stretchable,andwearableheatingdevices.30Liuetal.developedacarbonnanotube-basedfibrewithexcellentmechanicalandheatingproperties,whichcouldbestretchedrepeatedlyupto150%itsownlengthwithhighstabilityandreversibility.3iMeanwhile,multifunctionalw
12、earableelectronicsbasedonyarncomprisingAgNWswerealsoinvestigated.Zhaoetal.preparedapolymer-wrappedAgNWfibreforsimultaneousstrainsensingandheating,whichexhibitedarapid,reproducibleandstableresponseundertensilestrain(1-200%)andenabledhighheatingtemperatures.24Twokeyfactorsareusedtoevaluatetheefficienc
13、yofawearableheaterandstrainsensor:thestabilityofthetemperatureoutputduringdeformation,andthesensitivitytochangesintensilestrain.Toourknowledge,therearenoexamplesofasingleconductingyarnthatexhibitsbothhighlystableheatingandhighlysensitivesensingcapabilities.Mostofthereportedmultifunctionalyarnsexhibi
14、tedalowgaugefactor(GF),whichlimitedtheirsensitivitytofine,subtledeformation.Furthermore,thelongevityofthewearabledeviceswasshortsincetheconductivematerialsintheyarnwerepronetooxidationordetachment,whichmustbeovercomeforachievingwearabledeviceswithlong-termshelflifeandusage.5 Y b/8。N WULW co 人=已。Acn
15、enuo,q POPEO300 OZOZAsf 6Z u。pws=qndTherefore,thephysicalandchemicalstability;andthesensingperformanceofmultifunctionalyarnmustbeimprovedbeforetheycanbeusedinmarketable,wearableelectronicdevices.Toachievethis,wechoseaflexiblepoly(ethyleneterephthalate)(PET)rubbercore-spunthreadasasubstratefordeposit
16、edAgNWstoyieldaconductingyarn.TheAgNWswerethenprotectedfromoxidationanddetachmentbytheapplicationofinsulatingpolydimethylsiloxane(PDMS)layer,whichalsoservedtoimprovethestabilityoftheconductivepropertiesunderappliedmechanicaldeformation.FabricswovenfromthePET/AgNW/PDMSyarnwereusedtopreparemultifuncti
17、onalheatingandsensingmaterialwithhighstretchability,excellentheatingstability,andhighsensitivitytomechanicaldeformation.ResultsanddiscussionThefabricationprocessforthePET/AgNW/PDMSyarnwassummarizedinFig.1.YarncomprisingarubbercorewithanouterlayersuchasPETischeapandwidelyusedinthetextileindustry.32Th
18、erubbercorewastightlysheathedwithsixlayersofPETfibre,whichwerecross-woveninparallel(Fig.1).EachPETfibrewascomposedofmanybundledPETmicrofibres(Fig.S1,ESR),Rubber/PETyarnwasthencoatedwithAgNWsusingadrop-castingmethod.AgNWsweresynthesizedusingapreviouslydescribedpolyolreductionrouteinthepresenceofCl-an
19、dBr-ions.33-35Scanningelectronmicroscope(SEM)analysisrevealedthattheAgNWswereapproximately21nmindiameterandupto20minlength(Fig.S2,ESIt).Beforedrop-castingtheAgNWs,therubber/PETcorewaseitherstretchedto220%ofitsoriginallengthtoprepareayarnwithhighstabilityagainstmechanicaldeformation(Yarn220%)orfixeda
20、titsoriginallengthtoprepareyarnforsensingwithhighsensitivity(Yarn100%),InYarn220%,thedistancebetweeneachloopofthePETfibreincreased,whichallowedtheAgNWstoinfiltratebetweenthePETfibres(Fig,S3,ESI+).AdigitalUV/ozonesystemwasthenusedtocleanthePETsurfacesoforganicimpurities;andtoincreasethehydrophilicity
21、,wherethecontactangledecreasedfrom141.40to56.afterUV/ozonetreatment(Fig.S4zESIt).DuringtheUV/ozonecleaningprocess,theUVlightat254nmhelpeddecomposeloosely-boundorganicmatter,butwasalsoabsorbedbyPETyarnsurface.ThiscausedstrippingoftheoutermostsurfaceofthePET.Atomicoxygengeneratedbythephotonthencombine
22、dwiththeexposedsurfacelayermoleculesandtransformedthemintohighlyhydrophilicfunctionalgroupssuchas-OHr-CHOand-COOH.ThewettabilityofthePETsurfaceincreased,whichenabledastrongerassociationwithAgNWs.ThemorphologyofthePET/AgNWyarnwascharacterizedbyscanningelectronmicroscopy(SEM)(Fig.2).TheuntreatedPETfib
23、resurfacesweresmooth(Fig.2a),andbecameroughenedafterUV/Ozonetreatment(Fig.2b).AgNWsweremoreuniformlydistributedonpretreatedPETfibresurfaces,whichconfirmedthatUVOzonetreatmentwasbeneficaltotheadhesionofAgNWsontoPETsurfaces(Fig.2c-f).PhotographsofthePETyarnafterAgNWcoatingsshowedthatthecolourturnedfro
24、mwhitetodark-green,confirmingthattheAgNWswereevenlydistributedontheyarncore(Fig.S5,ESH).Finally,auniformPDMSlayerwasappliedtotheexteriorsurfaceusingtwodifferentcoatingmethodsforeitherYarn220%orYarn100%(seeExperimentalsection)(Fig.2g).Thisproduceddifferencesinthelayeredstructure,asobservedfromSEMmicr
25、ographsofyarncross-sections(Fig.2handi).InYarn220%,PDMScompletelyinfiltratedthePETfibresasitwasdepositedontoastretchedcore,whereasthePDMSonlycoatedtheoutermostsurfaceofYarn100%.BecausePDMSpossessesexcellentstretchabilityandflexibilityundermechanicaldeformation,itshoulddeformconformallywiththeunderly
26、ingyarnduringstretching.ThissuggestedthatthePDMScoatinginYarn220%wouldprovidegreaterstabilityagainsttensilestrain.36ThesensingandheatingcapabilitiesofthePETAgNWPDMSyarnwerethenexamined.Theirelectromechanicalperformancewasassessedbyexaminingthechangeinresistanceundervariousapplieddeformationmodes(Fig
27、.3).Theresistanceperunitlengthdecreasedfrom800to3whenthenumberofdrop-castingcycleswasincreasedfrom1to10(Fig.3a).Theincreaseindrop-castingcyclesledtoanincreaseinthequalityofAgNWcoating,quantifiedasmassperunitlength,whichexplainedthedecreaseofresistance.Atanevenhighernumbersofdrop-castingcycles,theres
28、istanceandqualitywereunaffected(Fig.S6,ESIt).TheimprovedconductivityofAgNWsathigherdrop-castingcycleswasattributedtoFig.1SchematicdescribingthefabricationofthePET/AgNW/PDMSyarn.PaperNanoscale5 Y b/80N WULW co A=SJPVUn enuo,q POPEO300 .OZOZAsf 6Z UOIXHJS-一 qnjFig. 2 SEM micrographs of (a) untreated P
29、ET yarn, (b) UV Ozone treated PET yarn. (c and d) Untreated PET yarn after three coatings of AgNWs. (e and f) UV Ozone treated PET yarn after three coatings of AgNWs. (g) The outer surface of the PET/AgNW/PDMS yarn, (h and i) Cross-sections of the PET/AgNW/PDMS yarn with PDMS coating 叩Plied when str
30、etched (h) or not stretched (i) (inset scale bar: 50 m).anoptimizedinterconnectionbetweenAgNWs.Thisprovidedthegreatestnumberofcoherentconductivepathwaysthroughoutthebulk,whichwasSimilartopreviousobservationswithAgNWswheretheresistancedecreasedafterannealingathightemperatures.37Inallproceedingstudies
31、,PETcoreswerecoatedwithAgNWsusingtendrop-castcycles,sincethisprovidedtheoptimalresistanceandquality.Theeffectoftensilestrainontherelativeresistancewasthenexamined(Fig.3b)3differentyarnsamplesunderdifferenttensilestrain:Yarn220%withoutPDMScoating,andYarn100%andYarn220%withPDMScoating.ThePDMS-freeYarn
32、220%displayeda2.5-foldincreaseinrelativeresistancewhenitwasstretchedto140%ofitsoriginallength(i.e.,40%tensilestrain).Inaddition,onlyaminor0.4-foldincreaseinrelativeresistancewasdisplayedbyPDMS-coatedYarn220%under40%tensilestrainbecausetheinterconnectivitybetweenAgNWswasmaintainedbythePDMSlayer,asdes
33、cribedabove.Incontrast,therelativeresistanceofPDMS-coatedYarn100%displayeda3-foldincreaseunder40%tensilestrain.Remarkably,therelativeresistanceofthePDMS-coatedYarn100%respondednon-lin-earlyunder100%tensilestrain.Insomecases,theuseofnonlinearstrainsensorscanimprovetheaccuracyofthereportedstrain.Moreo
34、ver,thevariationintherelativeresistancewaslinearwithtensilestrainwithin30%strainrange(Fig.S7,ESI+).ThishighlightedthecapabilitiesofPDMS-coatedYarn100%astheactivematerialinastrainsensingPET/AgNW/PDMSyarn.38ThechangeinthesurfacemicrostructureofPDMS-freeYarn220%causedbyanappliedtensilestrainwascharacte
35、rizedbySEM(Fig.S3,ESIt).Atatensilestrainof60%,thegapsbetweenPETfibresbecameenlarged,theinterconnectedAgNWnetworkwasdamaged,andtheresistancethereforeincreased.Asthetensilestrainwasincreasedfurtherto100%,nofurtherexpansionofthegapsbetweenPETfibreswasobserved;thusnofurtherchangesweremadetotheAgNWnetwor
36、kandresultingrelativeresistance.ForPDMS-coatedYarn100%,asimilareffectwasobserveduptoatensilestrainof40%.However,betweentensilestrainsof40%and100%,theAgNWsbecamereconnectedduetothecompressiveforcefromtheouterPDMSlayerontheinnercore,causingadecreaseinresistance.Finally,theimprovedtolerancetotensilestr
37、ainobservedinPDMS-coatedYarn220%wasattributedtothebackfillingofgapsbetweenPETfibreswithPDMSduringthecoatingprocess,whichprotectedtheinterconnectedAgNWsduringstretching.TheelectromechanicalperformanceofPDMS-coatedYarn220%wasalsoexaminedundervariousdeformationmodestoassessitssuitabilityforuseinwearabl
38、eheatingdevices(Fig.3c).Whensubjectedtodeformationbybending,therelativeresistanceincreasedbyonly10%whenthebendingradiuswasshortenedfrom10mmto1mm(Fig.3c).Meanwhile,therelativeresistancevariedbyamaximumof40%duringacyclicstretchingtestfeaturing1700cyclesat30%tensilestrain(1Hz)(Fig.3d);andbyamaximumof3%
39、duringacyclicbendingtest,featuring1000bendingcycles(Fig.3e).5 Y b/8。N WULW co 人=已。Acn enuo,q POPEO300 OZOZAsf 6Z u。pws=qndFig. 3 Electromechanical properties of the PET/AgNW/PDMS yarn. (a) Resistance and quality of AgNWs as a function of the number of dipping cycles. (b) Relative resistance variatio
40、n of the PET/AgNW/PDMS yarn before PDMS coating, PDMS coating at origin length, and PDMS coating at stretching length, (c) Relative resistance variation of the PET/AgNW/PDMS yarn that PDMS coating at stretching length under the different bending radius (straight, 10 mm, 5 mm, 3 mm and 1 mm respectiv
41、ely), (d) Relative resistance variation of the PET/AgNW/PDMS yarn in cyclic stretching (a strain of 30%) 1700 cycles (inset, cycles of middle part), (e) Relative resistance variation of the PET/AgNW/PDMS yarn in cyclic bending (bending radius of 10 mm) 1000 cycles (inset, cycles of middle part), (f)
42、 Changes in Relative resistance of the PET/AgNW/PDMS yarn after storage in air for different times, (g) Photos of LED brightness variation vs. elongation and release of the PET/AgNW/PDMS yam connected in the electric circuit.Significantly,thePDMS-coatedYarn220%exhibitedanincreaseinresistanceofonly7%
43、aftersixmonthsstorage(Fig.3f).Finally,theabilityofPDMS-coatedYarn220%tocarrysufficientcurrentwasexaminedbyincorporatingalengthofyarnintoacircuitfeaturinganLEDarray(Fig.3g).NosignificantchangestothebrightnessoftheLEDarrayweredetecteduponapplyingatensilestrainof70%tothePET/AgNW/PDMSyam,suggestingthata
44、nychangesinresistancecausedbyanincreasedstrainmadeanegligibleimpactontheconductivitythroughtheyarn.TheseelectromechanicaltestsdemonstratedthatthePET/AgNW/PDMSyarnwassuitablydurable,stable,andreliableforuseinwearableheatingdevices.TheeffectofstrainontheheatingperformanceofthePET/AgNW/PDMSyarnwasthena
45、ssessedbymeasuringthetemperatureoftheyarnbyinfrared(IR)imagingwhenvariousvoltagesandstrainwereapplied(Fig.4).Astheappliedvoltageincreased,thetemperatureoftheyarnalsoincreasedgraduallyuptoasaturationtemperature,whichwasshowntobestableoveratleast30satafixedvoltage(Fig.4a).Atemperatureof90wasachievedat
46、avoltageof5V.IRimagessuggestedthatthetemperaturewasuniformacrosstheentireyarnatallappliedvoltages,whichsuggestedthattheAgNWswereevenlydistributed.ThestabilityandreliabilityoftheheatingfromthePET/AgNW/PDMSyarnwerethenstudiedataconstantvoltageof4V,onayarnstrandofI=5cm,r=1.2mmandR11=10cm-1.Thetemperatu
47、reresponseofPET/AgNW/PDMSyarntotheappliedvoltagewasexaminedwithheatingcycles(Fig.4b).TheappliedvoltagewascycledfromOff(0V)toon(4V)every60s.Whenthevoltagewasapplied,thetemperatureincreasedrapidlyfrom30to53within30sduetothelowresistanceoftheyarn.Coolingoccurredatthesamerate.Nosignificantchangesinthehe
48、atingbehaviorwereobservedaftercyclingfor100times,whichsuggestedthattherapidJouleheatingpropertyofthePET/AgNW/PDMSyarnwassuitablystableandreliableforlong-termuseinwearableheatingdevices.TheheatingperformanceofthePET/AgNW/PDMSyarnwasthenfurtherstudiedbygraduallyincreasinganappliedtensilestrainin10%ste
49、pswhileapplyingafixed4Vvoltage.Theresistance(Fig.4c),andtemperature(Fig.4d)wererecordedintheentireexperiment.Theresistanceincreased,andthetemperaturedecreasedwhen20%tensilestrainwasappliedtotheheater,butbothwerestablebetween20%and100%strain.Nanoscale.5 Y b/8。N WULW co 人=已。Acn enuo,q POPEO300 OZOZAsf 6Z u。pws=qndTtaMTlot )Fig. 4 Thermal
