Strain-gauge sensoring composite films with self-restoring water-repellent properties for monitoring human movements

Flexible strain-gauge sensors are an essential constituent in smart electronic devices that can monitor the complex movements of people. We herein report a strain-gauge sensor with self-restoring water repellency, based on thermoplastic polyurethane (TPU)/multi-walled carbon nanotube composite films. TPU/carbon nanotube (CNT) composite films were simply fabricated by the filtration of CNT suspensions using electrospun TPU nonwovens as the filter paper. The strain-gauge sensors exhibited not only high sensitivity and durability, but also excellent self-restoring water repellency. The sensors performed well in monitoring a person's fingers, elbows, knees, and even neck movements. The self-restoring water repellency of the strain-gauge sensors originated from the hierarchical CNT networks on the TPU nonwovens. The “mesh-like” CNT networks would be cracked or broke under mechanical deformation, exposing the “feather-duster” structures underneath. The integrated hierarchical roughness mobilized the water droplets on the surface even under mechanical deformation. It is expected that the strain-gauge sensors will be applied in wearable electronic devices with super water-repellent properties. The work paves the possibility to fabricate high performance strain-gauge sensors that could be used in raining days or moist conditions.