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1、CHEMISTRYOFMATERIALSpubs.acs.org/cmArticleToughGel-FibersasStrainSensorsBasedonStrain-OpticsConversionInducedbyAnisotropicStructuralEvolutionTaoChen,XiaolanQiao,PeilingWei,GuoyinChen,InnocentTendoMugaanire,KaiHou/andMeifangZhu*CiteThis:Chem.Mater.2020,32,9675-9687PlReadOnlineACCESSIlllMetrics&More画A
2、rticleRecommendationsSupportingInformation.saoPJeP3qs=qnd2cqs M2aLUtDa- O- O cosuo三do-W s-zYnHoNOa.Ap。PeocMoABSTRACT:TheadvocacyofsmartlivingresultsinahighforwearableandfleibA2nqerstmonitorhumanmthSPCanCCrChcrlnnctrainnntircrnnprcinnnrattrartiPduettheirinherentelectricalsafetyandelectromagneticimmun
3、ityincomparisontostrain-electricityconversionsensors.Partlhydrogel-basedopticalIibersensorsarebiocompatible,stretchableandthusarepotentiallyapplicabletohealthmonitoring,IimitpdCU!Ie,andhuman-machineintelligence,andsoftrobots.NOnetheleqqHvdrogehapdntiralfiHprtilldAmnntratAchalpnArhadIimitpdctrptrhrat
4、inefrnmrhpmiralrrncc-linkinnnptwnrkcandincffiripntlighttransmittancefromdehydrationornucleationofwater.Herein,fleibleandstretchablestrainsensorsbasedonglycero-intmdurin11nancmnitphvdropfihpr(GN-Fibers)Waraach啜OdviadvnamirtrptrhinCfnrpartivpnrppfrnmmnmprnannarticlehvhridnrprrnrinCIVrarClwatprrncnk/pn
5、tTharpciiltantGN-FihaEQVClVarlWithanintrnnirmirrnctriirtnrACNivnlavincexcellenttensileStrenath(9.76MPa),hihelasticmodulus(32.63MPa),lowIiahtDrooaaationattenuation(0.26dBcm-Aandbroadstrainran11p.wintotheikpCfCIVnSrCI-water,suchGN-Fiharakoexhibitedln-tprmmiturp-rptaininandantifrpp7inproperties.Inaddit
6、ion,GN-Fibersfunctionedwellassensorsbasedonstrain-opticsconversiontomonitorstretchingandcompressingbehaviors.Itisbelievedthatsuchanopticalfiberbasedstrainsensorisagatewaytofabricationofnext-generationwearableandflexibledevicesforhealthmonitoringorartifcialintelligence.1.INTRODUCTIONTherapidgrowthofw
7、earablesmartdeviceshasresultedinahugedemandforsmartflexiblesensors,especiallythosedetectionwithinanarrowrangeofstrain(1IyIPa)hPrauAthplrAmnrnhniKarea,goodfleibility,andfacileassemblyproperties,3.4Sofar,strPcstructurequicklyfracturesuponhightensileloading.variouseffortshavebeendevotedtowardHeCtriral-
8、mediatedfihrstrainp11rhirhrpnnndtnmprhAirAdeformationsviaresistanceorcapacitancevariations.s,6However,theelectromagneticinterference(EMI)andelectricalsafetyissues(suchascurrentleakage)ofsuchmaterialshaverestrictedtheirfurtheraDDicabilitv.7OoticalmpdiatinhapdfihrprnnpinhprpntimmnitvtoFMTandintrinsicp
9、prtricSafEtvaswpIIasexcellentmultiplexingcapabilities,showinggreatprospectsaswearablestrainsensors.8,9Amongthem,silicon-basedinorganicoramorphousisotropicplastic(suchaspoly(methylmethacrylate)opticalfiberswithgoodtransparencyareverycommon.o-i3IncombinationwithBragggratingtechnology,suchopticalIibers
10、haveachievedstrainsensingviashiftingoftheBraggwavelengtharisingfromthestrain-opticsandqeometriceffects.14,isHowever,theyhavereceivedlimiteduseduetosomeimperfectionssuchasbrittleness,onlyallowingforInordertoovercomeshortcomingsassociatedwithsuchopticalfibers,thedevelopmentofnext-generationmaterialswi
11、thsuperiorelongationandstrengthishighlynecessary.Hydrogelsareconsideredtobesuchmaterialswithadjustableopticalperformance,softness,andwetness.i6,17Previousfindingsreportedahydrogel-modifiedglassopticalIiberviacoatingapolyethyleneglycoldimethacrylate(PEGDMA)hydrogelonaglassIibersurface.SuchanopticalIi
12、berwasprovedtotransformswelling-inducedhydrogelstructuralchangeintolighttransmissionvariationseffectively,thusrealizingifapplicationasaReceived:August16,2020Revised:November2,2020Published:November12,2020humiditySenSor,13ACSpublications2020AmericanChemicalS沁ty96754 3 2 1 0 Ooooo 11111 b (etSn3pos654
13、32IHNMRg46Time(min)591317DrawratioNO6007MS900Wavelength(nm)101(M92847Mf(求)OC三ECSH10Furthermore, excellent tensile properties and adjustable strength qualify hydrogel-based optical fi ber materials as promising novel fl eible strain sensors. Recently, Yun et al. demonstrated a series of biocompatible
14、 core-clad hydrogel 叩tical S bers in a tube mold with alginate and polyacrylamide as the hydrogel core and physically cross-linked alginate-Ca2 as the dad.19-21 The resultant hydrogel optical Ii bers exhibited high transparency and low light loss (400- 700 nm, -0.4 dB cm-). In addition, these optica
15、l fi bers could act as strain or glucose sensors by introducing response units, which responded to external stimulations via fi ber structural change induced light attenuation variations. Notably, the light transmission PrOPertieS of such materials could be adjusted via the design of polymer composi
16、tions and gel network structures. Therefore, hydrogel-based optical fi bers could9676Figure 1. FabricationandcharacterizationsofGN-Fibers.(a)Fiber-formingprocessforGN-Fiberfromtheprecursorsolutiontothepregelwithasubsequentpoststretchingprocess,(b)Time-dependentmoduliandtheircorrespondingderivatives(
17、inserts),aswellas(c)HNMRspectraforgelationprocessoftheprecursorsolutionforGN-Fiberi4-0.94.(d)Imagesof70cmlongGN-Fibeneu-0.94.(e)Drawratiodependentdiametercurveandcorrespondingimages(inserts)ofGN-FiberXM-aw(scalebar500m).(f)AAmratiodependentopticaltransmittancecurvesofGN-Gelsinthewavelengthrange400-9
18、00nm.(g)SEMimagesformorphologiesofGN-Fibeneu-0.94inradialandlongitudinaldirections,(h)imagesofthelightpropagationofGN-Fibe116i4-0.94forincidentlightofa650,515,and450nmlaser.functionwellasafantasticsignaltransmissionmediumandversatilesensor.However,previouslyreportedhydrogel-basedopticalfibersKavpCft
19、anhppnrnnfinpdtnrhpmiralrrnfeglycerol-watercosolventendowedtheresultantN-ibersapplicabilityforawj,temperaturerange,disp4r0antifreezingbehaviprs-aMboodjjmoisturepreservation.国狎QN-FiberftriuftTserveahumanmotionSensorsyia4Iheabilitytotransformstrainsintolightattenug)variations.Then,suchbasedstrainsenso
20、rsc*ld!howgreatpotentialtomoisturepreservation.sofdevelopedascext-genertibnWearabIeand.fle/i匕formedicalapplicationsanaartffid喝IIi能n弗E11IL宙i2. ResultandDiscussi2.1. FabricationofGNdH-Fitor-20XON2二二二二二二二二二：！Jghte*nttransmit23C50%RHafter1dSMChaGMFgK*2OX三23XCaniberdmgbyadynamicPC)StStetchipgprocessdepic
21、tedinFigUre1a.Indetail,acertainamountc*solutionsforaGN-Ge/uformapregel(anintermeandcross-linkedhydrogeThen,thepregelwasetrpoststretchingforfiber1E-3cwMX-*C23X-MX陈C)rcesstbf306990120150otheGN-Geh4-0.94precursorsolutionat22wasmonitoredTime(三)inrealtimebyarheologicaltechnique.AsshowninFigure1b,https:/d
22、x.doi.org/10.1021acsxhemmater.0c03342Chem.Mater.2020,32.9675-967-GN-FilMr-H-FiberGN-FilwrHF)3rGlycerol(wt.%)the polymerization process of the GN - Ge4- 0.94 precursor solution began immediately in the Ii rst 1.5 min (region i). Here, the loss modulus (G ) was higher than the storage modulus (G, ), s
23、uggesting a viscosity-dominated nature at the beginning (Figure S1). With increasing reaction time, both G, and Gu increased until they intersected at 1.5 min (loss factor (tan ) decreased to 0.3), which is generally defi ned as the critical gel point to demonstrate the formation of cross-linked net
24、works and the emergence of dominant elastic behaviors. As the time was further increased from 1.5 to 5 min (region ii), G, surpassed G, and continued growing to 5 103 Paz suggestinga relatively stable pregel1 which could sustain a poststretching process without fracture. Then, the pregel was extrude
25、d out, damped, and exerted dynamically poststretching to fabricate GN - FiberXM- 0.94. Notably, during the poststretching process, a chemical reaction was still involved to stabilize the fi ber shape, which is indicated by the slow increase of G, in Figure 1 b (region iii).28 Such a phenomenon could
26、 be also COnIi rmed byOEGMA and AAm (chemical shifts of 1.5- 2.0 and 5.5- 6.0 ppm) existed with the reaction time at 5 minf which gradually diminished from 5 to 11 min. Furthermore, FR spectra of GN - Fibeneu- 0.94showed a hydrogen-bonded band at 3200- 3400 cm-, Si- O vibration bands at 1003 cm- (cl
27、ay), amide group peaks at 1672 cm- (AAm)z and an ester group at 1714 cm- (OEGMA)1 confi rming the successful construction of GN-Fibers (Figure S2).After the poststretching process, 70 cm long GN - Fibers- could be successfully fabricated from a 4 cm long pregel1 suggesting relatively large scale fab
28、rication of GN-Fibers (Figure 1 d). This GN - Fibeneu- possessed a regular cylindrical-like cross-section morphology, whose diameter was 235 m and exhibited compact stacking gel networks (Figure 1g). The diameter of the resultant GN- FiberXWM4was adjustable in the range of 714 56.7 to 231 5.5 m via
29、varyinq the draw ratios from 200% to 1600% (Figure 1e and Figure S3). Notably, the corresponding GN - 6e4-zdisplayed excellent transparency for visible light ( = 400- 760 nm) (Figure 1f). With the addition of acrylamide, the hydrophilicity of GN-GeIs was enhanced, contributing to the increase in its
30、 light transmittance. Nonetheless, the addition of acrylamide could increase the viscosity of the precursor and reduce the draw ratio of the pregel. Therefore, to realize the combination of draw ratio and transmittance, the optimal molar ratio of AAm in comonomers for GN-Fibers was controlled to be
31、below 0.94. In addition, this good transparency contributed to the excellent light transmission performance of GN - Fiberl2 for visible light such as red (650 nm), green (515 nm) and blue (450 nm) lasers, respectively (Figure 1 h).2.2. Mechanical and Optical Stabilitv of GN-Fibers in a Widp TAmnArat
32、urp Ranae Thp introduction of Ivcp into GN-Fibers could reduce water evaooration and maintain thp cftnp CfCPl fi hrs hprap CfthP hvdrP-hndin interaction among glycerol, water, and polymer networks .31,32As seen in Figure 2al GN Fibeneu- 0.94 underwent only 22% liquid loss at the equilibrium state, r
33、emaining moist within 24 h and even longer. Thus, GN - Fibers- a“could be stretched and knotted after 24 h stored at 23 with a relative humidity (RH) of 50%. (Figure 2b) However, hydrogel fi ber(H-Fibe门614-o.%)withoutqlycerolquicklylostitsweightandalmostbecameadriedphasewithin5h,duetothefastevaporat
34、ionofwaterfromgelnetworks(Figure2a).Correspondingly,H-Fibeneu-0.94lostitsstretchabilityandfleibility(Figure2b).Inaddition,duetothehydm11pn-hnndinintprartinnhptwAAIvrprnlandWatPrthpformationoficecrystallatticesingelnetworkswasalsoinhibitedatsubzerotemperatures.Then,GN-Fibe116i4-0.94retainedgreatflexi
35、bilityandstretchabilityina-20environment,whereasH-Fibe116i4-0.94displayedstiffness(Figure2c).Specifically,thestrainatbreak(),tensilestrength()zandfractureenergy()of6-Fiberten-0.94waswellmaintained,indicatinggood,stable,andreproduciblemechanicalpropertiesafter24hstorageat+23or-20.(Figure2c).However,H-Fibe116i4-0.94almostlostitsoriginalmechanicalpropertiesunderthesameconditions,showingaremarkablelossofelasticityandsoftness(Figure2candFiqureS4).Furthermore,lowtemperaturescouldalsosharply
