Preparation And Sensing Properties Of Composite Hydrogel Materials

Hydrogel is a kind of soft wet material with high water content,similar to soft tissue,which has good biocompatibility,appropriate bioactivity and controllable geometry.Because of its adjustable properties,the study of conductive hydrogels has attracted the attention of researchers.However,conductive hydrogel has some shortcomings,such as low mechanical properties,poor environmental stability,low sensitivity,slow response time and recovery time,and can not be used in extreme conditions and external power supply,which limits its application in flexible wearable devices.In this paper,four kinds of conductive hydrogel materials were designed and synthesized in view of the existing shortcomings of conductive hydrogels,and their mechanical,conductive and sensing properties were studied respectively.The main research contents are as follows:(1)The hydrogel is prepared through a physicochemical driven process associated with binary media.Acrylamide(AAm)and vinyl acetate(VAc)undergo in situ radical polymerization in polyvinyl alcohol(PVA)/hydroxylated multi walled carbon nanotubes(m CNT-OH)water/dimethyl sulfoxide(DMSO)solution.The hydrogel sensor not only has excellent tensile strength,frost resistance and solvent volatility,but also shows excellent strain sensitivity(GF=6.39,in the range of 200～560%)because m CNT-OH forms a conductive path.The response time and recovery time are 80 ms and 60 ms respectively.After 260 cycles of measurement at 200% strain,the strain sensitivity will not decrease.The hydrogel sensor can stably track large or small human movements.Then,it has great potential in human-machine interface applications such as aphasia,physical exercise,or rehabilitation.(2)Li Cl loaded poly(acrylate-N-isopropyl propionamide)(PAA-NIPAm)hydrogel was prepared by UV crosslinking in ethylene glycol(EG)/H2 O.Hydrogels have good mechanical properties,such as 700% elongation at break and 20 KPa breaking strength,which can adhere to various substrates and resist frost and solvent volatilization.Especially,it has excellent conductivity of 8.51 S · m-1.Based on the change of resistance,the hydrogel shows a wide range of strain sensitivity,with GF reaching 5.84 in the range of 300%～700%.Its response and recovery time is very short,and it remains stable within 1000 cycles.In addition,the hydrogel is also assembled into a self powered device with an open circuit voltage of 0.74 V.This device can convert external stimuli such as stretching or compression into output current changes,thereby effectively detecting human motion in real-time.(3)4-(methacryloyloxy)ethyl-1-phenylene acid(MMBA)and 1,4-(5-hexenyloxy)benzene(RM26)were synthesized as supramolecular cross additives and inserted into polyvinyl alcohol(PVA)hydrogel.A series of conductive hydrogels(PVA PMR Na Cls)were prepared by salt leaching method.The most excellent toughness of PVA-PMR5-Na Cl is15.92 MJ · m-3,elongation at break is 600%,tensile strength is 5.61 MPa,and Young’s modulus is 2.16 MPa.It can withstand the side effects of salt water ions,as specific molecules with flexible chain segments and rigid groups intervene.Due to the carboxyl groups in the network,the conductivity of PVA-PMR5-Na Cl is 3.0 S · m-1 higher than that of the original PVA-Na Cl.It exhibits a high gauge factor(GF)for tensile strain,reaching6.24 above 200% strain.The PVA-PMR5 Na Cl sensor has high sensitivity,stability,and fast responsiveness in detecting human motion.In addition,a self powered PVA-PMR5-Na Cl sensor assembled with zinc and copper sheets achieved an open circuit voltage of 0.809 V,and can also track stretching,bending,and compression movements based on current changes.(4)On the basis of the previous part,an anti swelling hydrogel composed of polyvinyl alcohol(PVA),sodium styrenesulfonate(SSS),MMBA and RM26 copolymer was prepared.The hydrogel sensor exhibits high tensile strength(546%),high tensile strength(2139 KPa),high sensitivity(GF=4.76),fast response/recovery time(0.143 s and 0.123 s)and ultra-high transparency.On this basis,an underwater strain sensor has been developed,which is not only used for monitoring underwater movement in the environment,but also can detect fluctuations caused by water droplets falling from above.Therefore,this study provides a simple strategy for generating hydrogel sensors that can be used in the underwater environment,and expands the potential applications of wearable electronic devices.