Bilayer-structured carbon nanotube/ethylene–vinyl acetate flexible strain sensors with enhanced sensing performance prepared by biaxial stretching

Conductive polymer composites (CPCs) consisting of polymer materials and conductive nanofillers have excellent flexibility, ease of processing, as well as excellent mechanical and electrical properties, resulting in an enormous application potential in flexible strain sensors and other fields. In this paper, a flexible strain sensor consisting of an ethylene–vinyl acetate (EVA) copolymer/carbon nanotube (CNT) CPC with a bilayer structure was prepared by biaxial stretching. The results indicated that the conductivity of the composites gradually decreased as the stretching ratio (SR) increased, due to the major destruction to the conductive network caused by biaxial stretching. Biaxial deformation facilitates the dispersion and in-plane alignment of CNTs, thereby enhancing the property of the sensor. Compared with the unstretched CNT/EVA-EVA-1.0 bilayer-structured sensor [gauge factor (GF) = 89.4, monitoring range 0.5–50%], the CNT/EVA-EVA-1.5 bilayer-structured sensor (SR = 1.5) after biaxially stretched exhibited higher sensitivity (GF = 349698.2) and a wider strain monitoring range (0.5–120%). In addition, compared with monolayer CNT/EVA sensors, the bilayer-structured sensors exhibited higher stability, highlighting their good application prospects in health monitoring in the field of artificial intelligence.