| With the rapid development of information technologies such as 5G communications,Internet of Things and artificial intelligence,people’s lives are stepping into a new era of"Internet of everything".As the main source of people’s perception information and an important means of interacting with the environment,flexible wearable sensors are showing explosive growth at present.Flexible materials such as polyvinyl alcohol（PVA）,polydimethylsiloxane（PDMS）,and polyacrylamide（PAAm）,and conductive materials such as metal nanoparticles,GO,and carbon nanotubes was used to prepare common flexible wearable sensors.This kind of sensor converts the deformation signal of sensing material under mechanical action into electrical signal for monitoring.With the increasing demand for detection,it is expected that flexible wearable sensors not only have certain flexibility,but also need to meet the functional requirements of high sensitivity and self-healing.Therefore,a flexible sensor material with multiple functions is urgently needed.Hydrogel is a kind of three-dimensional polymer network that matches the modulus of human skin,and is regarded as an ideal material for the next generation of flexible wearable sensors due to its excellent tensile properties and good electrical conductivity.However,currently common chemical crosslinked hydrogels usually lack comprehensive properties such as adhesion,self-healing and degradability,which cannot meet the needs of wearable devices.In addition,traditional hydrogels are easy to freeze in a low temperature environment due to their large amount of water,and lose water rapidly in a high temperature environment,resulting in a sharp decline in performance.Therefore,the stability of hydrogel is also an urgent problem to be solved.It is of great significance to develop moisturizing hydrogels with tensile,adhesive,self-healing and conductive properties for flexible wearable sensor applications.In this paper,MXene/PAA hydrogel was prepared by sol-gel method,and the antifreeze and moisturizing performance of hydrogel was endowed by solvent replacement method,and its application in the field of flexible sensor was studied.The specific contents are as follows:（1）Due to the low sensitivity and narrow detection range of the sensor,a multifunctional conductive hydrogel（MXene/PAA）with high sensitivity and wide detection range was prepared.In this system,two-dimensional MXene（Ti3C2）material with excellent hydrophilicity,high specific surface area and metal conductivity was used as conductive filler,polyacrylic acid（PAA）formed by free radical polymerization of acrylic acid（AA）monomer was used as hydrogel matrix,ammonium persulfate and N,N’-methylene bisacrylamide were used as initiator and crosslinking agent.MXene/PAA hydrogel was prepared by sol-gel method,in which MXene nanosheets and PAA matrix network were firmly bonded by hydrogen bond interaction.In this system,the tensile properties,adhesion and electrical conductivity of hydrogels are regulated by regulating the mass ratio of MXene/AA,so as to coordinate the mechanical properties and electrical conductivity of wearable sensors.The detection range and sensitivity of hydrogel sensor were characterized by stress-strain test and resistance test.The experimental results show that by optimizing the mass ratio of MXene to AA,the obtained MXene/PAA hydrogel sensor not only achieves a wide detection range of 1050%,but also achieves a sensitivity of 4.94.In addition,hydrogels have many functions such as self-healing,self-adhesive,biocompatibility and biodegradability.We apply it to the wearable strain sensor,which can realize the effective detection of human motion signal.This work provides new ideas for the development of the next generation of flexible,self-healing adhesive sensors and electronic skins for the field of human-computer interaction.（2）For the problem of poor antifreeze and moisturizing performance of MXene/PAA hydrogel in Chapter 1,glycerin solvent replacement strategy was adopted to improve the antifreeze and moisturizing performance of MXene/PAA hydrogel sensor.In this system,water molecules in MXene/PAA hydrogel were replaced by glycerin solvent to obtain MXene/PAA composite gel with water and glycerin as the mixed solvent.Glycerol can form strong hydrogen bond interaction with water molecules,which not only prevents the evaporation of water molecules but also inhibits the formation of ice crystals at low temperature,which makes the composite gel have good frost resistance and moisture retention performance.In this system,the sensor performance and antifreeze moisture performance of the composite gel were balanced by optimizing the solvent replacement time.The detection range and sensitivity of hydrogel sensor were characterized by stress-strain test and resistance test.When glycerol and water are used as mixed solvents,the hydrogen bonding between glycerol and water expands the detection range and sensitivity of gels.The test results of rotary rheometer show that the hydrogen bond between glycerol and water can inhibit the formation of ice crystals at low temperature,which endows the composite gel with good frost resistance.In addition,the composite solvent can effectively enhance the moisturizing performance of the gel,which provides a solution to the problem of water loss.We connected the electrical signal of the hydrogel to the mobile phone through bluetooth to realize wireless monitoring of human movement,providing a new idea for remote monitoring of human life activities at low temperature. |
