Preparation And Application Of Graphene-based Flexible Strain Sensors

Because of the flexible strain sensor has stretch-ability,flexibility and can fit with human skin,so it has received widespread attention from researchers in the fields of human motion detection,health monitoring,human-computer interaction and electronic skin.In recent years,graphene has become the most novel conductive filler because of its excellent conductivity and mechanical properties.But choosing an appropriate compound method is the decisive factor for graphene to exert the best conductivity in the composite matrix.In this paper,the goal is to develop a flexible strain sensor with high sensitivity and a wide working range.Through emulsion blending and ultrasonic-assisted supercritical CO2 fluid method,the feasibility of graphene(GE)in constructing a three-dimensional conductive network in natural rubber(NR)matrix is verified,and the influence of the process method on the performance of the flexible strain sensor is determined.The sensing mechanism,influencing factors of performance and practical human detection applications of flexible sensors were studied in this artical.The main research contents and results are as follows:(1)Preparation of graphene flexible sensor by emulsion blending methodA conductive material with a three-dimensional conductive network is prepared by dissolving colloidal NR with a suspension of GE,and then through ultrasonic dispersion,evaporation,and flocculation process steps.According to the study of the mechanism of the preparation process and the analysis of the microstructure of the components,it was found that GE remained uniformly dispersed in the matrix and the rubber molecular chain was integrated into the three-dimensional conductive network with GE as the core.According to the influence of tensile behavior on the conductive network,the sensing mechanism of the sensor is based on the deformation of the conductive network in the matrix and the change of the resistivity of the material.Performance tests show that the percolation threshold of conductive materials is as low as 1.8 vol%,and the conductivity is as high as 0.005 S/m under a 2.5 vol%GE load,which is four orders of magnitude higher than materials prepared by other methods under the same load,gauge factor up to 46.The excellent repeatability and stability shown in human motion testing(including vocal cord vibration,pulse,heartbeat,joint bending,etc.)make it shows good application value(2)Preparation of graphene flexible sensor by ultrasonic assisted and supercritical CO2 fluid impregnationFor the first time,the ultrasonic-assisted scCO2 fluid method was used to inject GE into the expanded NR matrix.The analysis of the expansion mechanism of NR in scCO2 fluid provides a theoretical basis for GE to be successfully injected into the matrix.Combining the factors of the impregnation medium,the ultrasonic time,the decompression mode and NR cross-linking degree to study the injection effect of graphene,the optimal process conditions were determined.The results show that the depth of GE injection into the matrix is 27-35 ?m,the loading of GE is 0.34 vol%at the maximum,and the conductivity of conductive materials before and after hot-press vulcanization is as high as 0.2 and 0.02 S/m,respectively.Compared with similar materials the conductivity is at the leading position with lowest graphene loading,and gauge factor up to 30.The good stability and excellent accuracy shown in human motion testing not only make it show great potential in application,but also provide a newly and environment friendly process idea for the industrialization of flexible sensors.