Preparation And Properties Of MXene Modified Hydrogel Flexible Strain Sensor Based On Melamine Sponge As Skeleton

Due to its advantages of good flexibility,light,small and portable,low production cost and good biocompatibility,flexible sensors have broad application prospects in today’s information and digital society.However,most of the sensors on the market only have a single function,and flexible sensors with wide detection range,high sensitivity,fast response time,low hysteresis and high durability have received widespread attention,but it is difficult to break through the bottleneck from experiment to mass production,and can not move towards large-scale and industrial applications.Therefore,it is of great scientific and practical significance to develop flexible sensors with excellent sensing performance,high practicability and low cost.In this work,the microstructure,mechanics and sensing properties of two kinds of three-dimensional flexible sensors,the melamine conductive sponge and the polyvinyl alcohol/sodium alginate/MXene conductive hydrogel,were studied respectively.On this basis,the scheme of filling the melamine conductive sponge into the polyvinyl alcohol/sodium alginate/MXene conductive hydrogel was proposed for the first time.The compression resistance of PVA/sodium alginate/MXene conductive hydrogel was improved to some extent,and a new flexible sensor with good sensing performance was successfully prepared.The main contents and results of this paper are as follows:（1）MXene@chitosan/melamine sponge flexible strain sensor.The MCM（MXene/CS@MS）flexible sensor with good electrical conductivity was prepared by uniformly loading the negatively charged MXene nanosheets on the skeleton of a melamine sponge（MS）coated with chitosan（CS）,and the positively charged CS and MXene were closely bonded under the action of electrostatic force.The research results show that the sensor has excellent sensing performance,which is not affected by the loading rate,and the relative variation amplitude of the resistance under constant compression strain in the range of 0-100%is basically unchanged.Moreover,it has a high sensitivity of 0.334 k Pa^-1in the compression range below 75%.The response and recovery time are less than 0.5 s,and the resistance changes little under 1000 times of compression-release cycle test,which has strong application potential under 50%constant compression load.（2）Polyvinyl alcohol/sodium alginate@MXene hydrogel flexible strain sensor.MXene was uniformly dispersed in polyvinyl alcohol（PVA）and sodium alginate（SA）with different viscosity,and the two were mixed by freeze-thawing according to different mass ratios to obtain PSM（PVA/SA@MXene）hydrogels with different elastic modulus.After SEM analysis,combined with electrical conductivity and swelling performance data,PSM hydrogel with low viscosity SA content of 40 wt%was selected for sensing performance analysis.The results showed that it had a detection upper limit of about 18k Pa under a large compression strain of 80%,and showed good stability under a compression strain of less than 40%.The relative change of resistance is basically not affected by the loading rate,and the compression strain sensitivity factor of 25%-35%at the loading rate of 100 mm/min is about 2.22（GF value）,and good sensing characteristics are still maintained after 500 cycles of compression and release at the loading rate of 100mm/min.When a constant compression strain of 50%is applied at a loading rate of 500mm/min,there is a faster response time（240 ms）and recovery time（360 ms）.（3）MXene@polyvinyl alcohol/sodium alginate@melamine composite hydrogel flexible strain sensor.By combining the contents of（1）and（2）,PVA and SA were crosslinked between the skeleton of melamine sponge,that is,the sponge was filled into the PSM hydrogel network.MPSM（MXene@PVA/SA@MS）composite hydrogels with good electrical conductivity,low swelling degree and excellent pressure bearing capacity were obtained and selected by using the similar method described in（2）.When the high viscosity SA content is 40 wt%,the performance is the best.At the loading rate of 5mm/min,the compression strain sensitivity factor is about 1.93（GF value）in the range of30%to 45%,and it has good strain cycle stability and durability.Good sensing characteristics can be maintained for a long time after 500 cycles of compression and release at a loading rate of 500 mm/min.It is worth noting that although the scheme sacrifices part of the sensing response time,it basically solves the problem of cracking of pure PSM hydrogel matrix in terms of mechanical properties,achieving the expected goal,and points out that further research can be carried out on the basis of this enhancement strategy.