Preparation, Performances And Applications Of Flexible Pressure Sensor Based On Porous MWCNTs/Ecoflex Composites

The flexible sensors have great potential applications in flexible electronic skin,mobile medical aids,energy collection,and flexible touch screen,and so on.These applications are involved to human touch.Therefore,the flexible sensors are required to have a high sensitivity under the low pressure range.For the flexible capacitive-type pressure sensor,the porous structures were used to improve the sensitivity of sensor,due to the high compressibility of the porous structure and the increase of the dielectric constant in compression process.According to above-mentioned results,the sensitivity of sensor can be further improved by improving the dielectric constant of porous dielectric layer.The polymers were used as dielectric layer of the flexible sensors usually.The reported results presented that the dielectric constant of polymers can be improved by composite with multi-wall carbon tubes?MWCNTs?.Herein,Ecoflex is chosen as the matrix.The capacitive-type pressure sensor was assembled by using the MWCNTs/Ecoflex composites and Ecoflex film with MWCNTs layer as dielectric layer and electrodes respectively.The performances of sensor were studied and the improvement mechanism of sensitivity was discussed.The details are as follows:The salt particles with various sizes were extruded into the cube shape in the mold as template.A porous structure of Ecoflex was formed by molding Ecoflex within this cube template.A parallel plate capacitive pressure sensor was prepared.The response of the sensors increases with the pressure in the pressure range of 0-100kPa,and the response of the sample with a pore size of 450-500?m is the highest.The sensitivity of the sensors decreases and then increases with the increase of the pore diameter of porous dielectric layer in the low pressure region.The sensitivity of sample with 150-200?m pore diameter is about 1.09 kPa^-1.All samples have obvious hysteresis and good stability,which can be used to detect finger bending and palm fisting.The mixtures of salt particles?diameter about 250-300?m?and MWCNTs were extruded into the cube shape to prepare porous MWCNTs/Ecoflex composites with the 0.3 wt%,0.65 wt%,1 wt%MWCNTs contents.The pressure sensors based on the porous MWCNTs/Ecoflex composites were synthesized by the same process.In the 0-100 kPa pressure range,the response of the sensor increases with the pressure,and the response of the composite sensors is much higher than that of the pure Ecoflex samples.The sensitivity increases with MWCNTs contentsin the low pressure region.The sensitivity of the sample with 1 wt%MWCNTs is the highest,about 2.306 kPa^-1,which is 4.2 times that of the pure Ecoflex sample.The addition of MWCNTs significantly improved the sensitivity of sensors,because the dielectric constant of the composites was increased.Moreever,The addition of MWCNTs decreses the hysteresis of devices and improves detection limits of devices.The results provide a feasible way to improve the sensitivity of pressure sensor.The MWCNTs/Ecoflex sensors can detect the pulses of carotid artery and heartbeats of a human.The results show the flexible sensor has potential applications in the wearable medical auxiliary device and the electronic skin.