Piezoresistive Properties of Multi-Walled Carbon Nanotube/Silicone Rubber Composites under Cyclic Loads with AC Excitation

Multi-walled carbon nanotube (MWCNT)-filled silicone rubber (SR) composites were prepared as piezoresistive materials for pressure sensing applications, with MWCNT concentrations from 0.5 wt% to 6.5 wt%. Samples were compressed under successive loading–unloading cycles with alternating current (AC) excitation, and electrical admittances were measured using interdigital electrodes. Then the piezoresistive properties were obtained and explored. Experiment reveals negative piezoresistivities with exponential performance characteristics for all concentrations. Furthermore, piecewise polynomial approximations of the performance characteristics are established to simplify the design of circuits. As the MWCNT concentration increases, the proper measurement range broadens, and the sensitivity in this range increases. However, the repeatability and hysteresis appear relatively poor far above the percolation threshold; both show minimums near the percolation threshold, with values of 2.3% and 16.1% respectively. The repeatability and the hysteresis varying with the MWCNT concentration are interpreted as the recovery capabilities of the conducting networks varying with the distribution densities of nanotubes. Achieved results serve to guide the development of piezoresistive nanocomposite sensors. (paper)