Hollow-porous fiber-shaped strain sensor with multiple wrinkle-crack microstructure for strain visualization and wind monitoring

Flexible strain sensor shows great development prospects in medical treatment, human-machine interface and environmental monitoring fields due to their great flexibility, ductility, skin-mountability and excellent sensing abilities. Nevertheless, the inherent contradictions between sensitivity and sensing range limit their further development as high-performance strain sensors. To solve this challenge, a two step pre-stretching strategy was proposed in this paper. Wrinkle and crack structures on carbon nanotubes (CNTs) conductive layer were integrated into a thermoplastic polyurethane (TPU) fiber with hollow-porous structure. Benefiting from the synergistic structure of the conductive layer, the fiber-shaped strain sensor synchronously possesses a wide sensing range (up to 530 % strain), high sensitivity (gauge factor, GF up to 57.2), low detection limit (0.5 % strain) and satisfactory sensing stability and durability. The sensing mechanism was proposed based on the development of the conductive network and the wrinkle and crack microstructures in detail. Moreover, strain-dependent visualization of the sensor under ultraviolet (UV) light was realized on the basis of the good UV-shielding property of the CNTs layer and the exposure of fluorescent agent (FA) in TPU fiber during the crack propagation process. This fiber-shaped strain sensor was demonstrated for human bio-signals acquisition as well as the monitoring of wind direction, showing its broad application prospects as next generation flexible strain sensor.