Preparation And Performance Study Of Multiple Conductive Materials And PDMS Composite PI Sponge Flexible Piezoresistive Sensor

Polyimide（PI）sponge-based flexible piezoresistive sensors have the basic advantages of high and low temperature resistance,and can be used normally in extremely cold and extremely high temperature environments.However,the low sensitivity,narrow detection range and the shedding of conductive phase still need to be further studied..Based on the above problems,this paper studies and optimizes the performance of PI sponge based flexible piezoresistive sensor from the design and construction of sensing materials and the improvement of flexible substrate.Based on the design and construction of three-dimensional multi-carbon hybrid conductive network,organic-metal interconnection conductive network,silicone rubber-PI sponge flexible blending substrate,Multiple conductive carbon material/PI composite sponge flexible piezoresistive sensor,polypyrrole-silver（PPy-Ag）/PI composite sponge flexible piezoresistive sensor,graphene-polydimethylsiloxane（GE-PDMS）/PI composite sponge flexible piezoresistive sensor.The specific works are as follows:Carbon black（CB）,single-wall carbon nanotubes（SWCNTs）,MXene and reduced graphene oxide（rGO）with different dimensions were attached to PI sponge walls by vacuum impregnation method to construct multi-dimensional conductive carbon material/PI composite sponges.The effects of carbon material ratio and hydrothermal reduction time on the performance of the composite sponge flexible piezoresistive sensor were studied.The results show that the"synergistic effect"between multiple conductive carbon materials has a great influence on the electrical performance of the sensor.The sensitivity of rGO-CB/PI composite sponge flexible piezoresistive sensor can reach and stabilize at 0.875 kPa^-1.The sensitivity of the rGO-CB-SWCNTs/PI composite sponge flexible piezoresistive sensor is up to 1.436 kPa^-1.The sensitivity of rGO-CB-Mxene/PI composite sponge flexible piezoresistive sensor is up to3.551 kPa^-1,and the detection limit is as low as 3 Pa.After 6 h of 450℃and-196℃extreme conditions,the sensor can be used normally,the response time is as low as 0.24 s,and the electrical signal can still output stably after 1000 compression cycles.By regulating the mole ratio of pyrrole（Py）and silver nitrate（AgNO₃）and the pH value of the reaction solution,organic-metal interconnected conductive network was constructed,it was found that the size of PPy and nano-silver generated under the conditions of n（Py:AgNO₃）=36:50 and pH=3.61 was the most uniform.PPy adhered uniformly to the surface of PI sponge and firmly fixed the nano-silver on the sponge effectively.The two conductive materials together form a tightly arranged three-dimensional interconnected conductive network.The sensor has a sensitivity of 16.31 kPa^-1 in the range of 0-80 Pa,which is a significant improvement over the sensitivity of the previous PI sponge based flexible piezoresistive sensor of around 1 kPa^-1,while showing better linearity.The sensitivity in the stress range of 80 Pa-3 kPa is also maintained at about 0.116 kPa^-1.By adjusting the compound amount of GE and silicone oil,the hybrid flexible substrate could be constructed.The GE-PDMS/PI composite sponge sensor had the best performance when the GE additive amount was 12 wt%and the silicone oil concentration was 25 wt%.The sensitivity is-1.04 kPa^-1 in the low stress range of 0-700 Pa.The sensitivity remains at 0.108kPa^-1 in the stress range of 4.5-8 kPa.The effective detection range of the PI sponge-based flexible piezoresistive sensor is extended to 30 kPa.After 1000 times of continuous cyclic compression,the size of composite sponge did not change,nor did GE fall off,indicating that the mixed substrate formed by PI sponge coated by PDMS has a sufficient protective effect on the conductive phase.