Design strategy for hierarchical structure of carbon black on microporous elastomer surface toward stretchable and compressive strain sensors

Flexible mechanical sensors capable of sensing both compressive and tensile strains with high sensitivity and linear piezoresistive response are of great significance for the development of wearable devices, flexible electronic skins, and robotics. However, it is still of challenge to develop simple 3-dimensional (3D) porous polymer/ carbon nanomaterial composite strain sensors capable of sensing both tensile and compressive strains with reproducible electrical signals. Herein, we report a simple and scalable morphology-engineering strategy, i.e., selective location of carbon black (CB) in polyoxyethylene (PEO)/ethylene-alpha-octene random copolymer (ORC) blends via phase separation, to fabricate isotropic 3D continuous porous composite strain sensors. Such a composite consists of a continuous porous ORC matrix inlaid with preferable CB distribution on ORC surface after PEO removal, enabling distinguishable detection of both compressive and tensile strains with opposite resistance changes. Specifically, the as-fabricated strain sensors exhibit linear response with a sensitivity of 16 for 0-46% compressive strain, a detection limit of 0.3% strain with 16/16 ms response/recovery time. Besides, it has a large gauge factor for tensile strain of 0-300%, a detection limit strain of 0.06% with 16/47 ms response/recovery time, and low hysteresis degree. As such, it allows for full-range body motion monitoring and Morse code communication.