Piezo-capacitive behavior of a magnetically structured particle-based conductive polymer with high sensitivity and a wide working range

Abstract

Conductive polymers (CPs), which consist of conductive particles dispersed in a flexible polymer matrix, are an emerging material for application in flexible tactile sensors due to their piezo-capacitive effects. We employed a magnetic field to synthesize a CP, i.e., a magnetically structured nickel–silicone rubber composite (S-NSRC hereafter), in order to maximize its sensitivity as well as its working range. The S-NSRC-based sensor features extraordinary sensitivity, e.g., a S-NSRC can achieve up to 460 kPa⁻¹ in value, which is orders of magnitude higher than those of its traditional counterparts. Meanwhile, S-NSRC occupies a wider working range (around 200 kPa) because the dispersed particles reinforce its Young's modulus. We also demonstrate its high temperature stability, where the capacitance change from 30 °C to 100 °C is only 3.5% of the resistance change (the piezo-resistive effect). The piezo-capacitive behavior of S-NSRC is studied under the impacts of curing field strength, field direction and particle volume fraction. Additionally, the piezo-resistive behavior, response time, hysteresis and loading rate effects are investigated experimentally. We found unusual piezo-capacitive behaviors for S-NSRC, such as strong nonlinearity, decreasing capacitance after saturation, and breakdown behavior. These behaviors are a macroscopic reflection of how well the particles rearrange their spatial distribution under compression. All these behaviors can be readily interpreted by analysis of the rearrangement of the particles under compression along with the evolution mechanism of the initial distribution of particle microstructures induced by different magnetic field levels.