Conductive Cross-Linkable PDMS-MXene Nanosheet Networks on Polyurethane Sponges as Robust Superhydrophobic Sensors for Human Motion Detection

Wearable piezoresistive sensors have aroused considerable attention for their huge potential in emerging applications such as healthcare monitoring and intelligent electronics. However, the fabrication of piezoresistive sensors that combine excellent sensing performance with outstanding working reliability in watery environments still remains challenging. Herein, a superhydrophobic polyurethane (PU) sponge was proposed as a piezoresistive sensor through the synthesis of d-asparagine-modified MXene nanosheets (MXene-NH2) and coating of a conductive cross-linkable layer constructed by dihydroxyl-terminated poly(dimethylsiloxane) (PDMS(OH)) and MXene-NH2 nanosheets. The microscale sponge skeleton and nanoscale PDMS-MXene nanosheet wrinkles formed a hierarchically rough structure in support of superhydrophobicity with a water contact angle of 160 degrees. Benefiting from the chemically cross-linkable network and strong adhesion of PDMS-MXene nanosheet coating, the obtained PDMS-MXene@PU sponge exhibited a robust water repellency with water contact angles (WCAs) larger than 150 degrees after enduring chemical and physical damages. Owing to the synergistic effect of the production of microcrack junctions in the PDMS-MXene nanosheet layer and contact separation between conductive backbones, the PDMS-MXene@PU sensor was successfully applied in monitoring full-scale human motions (e.g., blowing, facial expression, finger and knee bending, etc.) with excellent sensing performances of the gauge factor reaching -1.9. The findings conceivably stand out as a methodology to fabricate robust superhydrophobic piezoresistive sensors with desirable sensing property for innovative and broad applications even under special working conditions.