An ultra-lightweight and hydrophobic piezoresistive foam with super-wide strain and pressure detection range

Abstract

Achieving a piezoresistive sensor with extensive strain and pressure response range for subtle and large motion detection remains a formidable challenge. Furthermore, an advanced parameter (waterproof capability), which is critical for wearable sensors, has received insufficient attention in current research. Herein, macroscopically segregated polyolefin elastomer (POE)/carbon nanostructures (CNS) foams with a super-low density and superior waterproof were fabricated via supercritical CO2 foaming, revealing a facile and eco-friendly process. Compared to piezoresistive foams with randomly distributed structure, POE/CNS foam sensors with macroscopically segregated structure displayed an ultra-low density (∼0.1 g/cm3), and apparently improved piezoresistive behavior. Additionally, the segregated POE/CNS foams exhibited a remarkably lower percolation threshold of around 0.011 vol%, enabling stable piezoresistive capability even with an ultra-low CNS content of approximately 0.0043 vol%. Therefore, the prepared POE/CNS foam sensors (FCNS0.1 and FCNS0.5) demonstrated an exceptional strain and pressure response range (0.5%–90% compression strain and approximately 0.5–3700 kPa), and the foam sensor (FCNS0.5) displayed a broad linear strain response range from 10% to 90% compression strain. Moreover, the segregated POE/CNS foams exhibited good hydrophobicity, enabling the piezoresistive foam (FCNS0.5) to maintain its sensing ability underwater. These outstanding piezoresistive performances enabled the foam sensors to monitor diverse human motions including subtle and superhigh pressure. Consequently, piezoresistive foams with exceptional performance and versatile applications lay the foundation for the development of the next generation of foam sensors.