Balancing sensitivity, hardness, and response speed in flexible piezoresistive sensors in room-temperature-vulcanized silicone rubber, carbon black, and multiwalled carbon nanotubes via multiparameter-material design

Abstract Flexible piezoresistive sensors are attractive for structural health monitoring; however, the simultaneous optimisation of sensitivity, mechanical compliance, and response speed remains challenging. In this study, room-temperature vulcanized methyl silicone rubber (RTV)/carbon black (CB)/multiwalled carbon nanotube composite sensors are fabricated by solution blending, and the coupled effects of a silane coupling agent (KH-550) and RTV-matrix viscosity on the mechanical, electrical, and sensing performances of the composite are systematically clarified. KH-550 reduces the percolation threshold, lowers bulk resistivity by up to 26.54% at 15 phr CB, and enhances pressure sensitivity by 48.45%, while inevitably increasing hardness. Matrix viscosity is shown to be a key regulator of the dynamic response: decreasing viscosity from 1500 to 300 mPa · s shortens both response and relaxation times by more than 50%. By combining experiments, ABAQUS and stochastic network simulations, we suggest that anomalous piezoresistive behaviour is more likely to occur when the conductive fillers are near the percolation threshold and the conductive network is relatively fragile. Finally, we introduce a dimensionless figure-of-merit F that integrates normalised sensitivity, hardness, and response speed, and construct a bubble chart that identifies a practical window (CB ⩾15 phr, moderate viscosity and 3 phr KH-550) for balanced performance. This study provides a reference for the design and compositional optimisation of functional materials for high-performance flexible piezoresistive sensors.