Chitosan Wrapped Graphene/Polyurethane Composites with Improved Dielectric Properties for Capacitive Sensing

The development of flexible capacitive pressure sensors with high sensitivity and fast response demands the need for thin dielectric films with excellent mechanical flexibility and remarkable dielectric properties. Herein, a graphene/polyurethane (TPU) dielectric was designed by dispersing graphene fillers into TPU elastomer through chitosan (CS) modification. The dispersion of graphene fillers in the TPU matrix can be effectively improved by using CS as mediating agents, thus further elevating the dielectric properties of the composites. The as prepared dielectric films exhibit high permittivity (90), low dielectric loss (0.02) and remarkable flexibility. Afterwards, the flexible dielectric films were employed to construct capacitive sensors by integrating the top electrode, dielectric layer, and bottom electrode into a sandwich structure. Taking advantage of the high permittivity of the dielectrics and the microcapacitors generated between graphene fillers, the corresponding sensors exhibit high sensitivity to loaded pressure (S = 0.53 kPa–1 for the range 1.6–4.8 kPa) and out-of-plane bending (S = 0.08 deg–1 for the range 0 ~ 150°). In addition, a 3 × 3 sensor array was successfully fabricated and applied in the real-time monitoring of water drop, sensing subtle touch, and mapping the spatial distribution of pressure. The fabricated sensors demonstrate promising potential in the application of human-machine interfaces and wearable devices.