A Double-layer Carbon Nanotubes/Polyvinyl Alcohol Hydrogel with High Stretchability and Compressibility for Human Motion Detection

Abstract

With the development of technology and the improvement of living standards, hydrogel-based strain sensors have attracted more attention. However, fabrication of hydrogel strain sensors with desirable mechanical and piezoresistive properties is still challenging. Herein, a double-layer flexible hydrogel sensor is presented, which is made of carbon nanotubes (CNTs) and polyvinyl alcohol (PVA) with high stretchability up to 415% strain and supercompressibility to 92% strain, and considerable electrical conductivity (1.11 S m-1). The hydrogel sensors show great linearity throughout the detection range, excellent durability and stable relative resistance change (∆R/R0) during 1000 loading-unloading cycles. These excellent properties are attributed to a new double-layer structural design, i.e. a thin conductive sensor layer of CNTs/PVA deposited on a pure strong PVA substrate. Combined with fast response time (508 ms at stretch and 139 ms at compression) and biocompatibility, this new sensor offers great potential as a wearable sensor for epidermal sensing applications such as detecting bending of human joints, swallowing, breathing, etc. Besides, the CNTs/PVA hydrogel can operate electronic screens due to its internal ions, and even use mechanical signals to modulate light signals. All of these demonstrate the great advantages of the CNTs/PVA hydrogels as strain sensors.