Fabrication of superhydrophobic conductive film at air/water interface for flexible and wearable sensors

Flexible and wearable sensors are of extreme importance for various practical applications in complex environments, such as electronic skin, body motion detection, etc. However, preparation of cost-effective and superhydrophobic wearable sensors with excellent flexibility, anti-corrosion, outstanding sensitivity and environmental adaptability remains challenging. Herein, a superhydrophobic flexible film is fabricated by spray-coating thermoplastic elastomer (TPE) solution on the upside of a multi-walled carbon nanotube (MWCNTs) sheet formed at the air/water interface, followed by treating the downside of MWCNTs sheet with polydimethylsiloxane (PDMS) pumped into the water. In the process, the covering of TPE on the MWCNTs made the sheet shrunk and increased the density of the conductive network. PDMS coating enhanced superhydrophobicity of the film, and binding fastness of the MWCNTs. The obtained sandwich-like TPE/MWCNTs/PDMS film had superior conductive sensitivity, large strain range (80%), fast and stable response time (60-80 ms) with great stability over 1000 stretching-relaxing cycles. Benefiting from the favorable superhydrophobic property, the fabricated film was capable of being put into liquid environment for quantifying the resistance under humid environments including moisture, acid, basic and salt conditions. It can be effectively used to measure wrist pulse and monitor various movements associated with different human body joints, such as finger, wrist, elbow. Moreover, the sensing film was able to capture the continuous signals in diverse atmosphere such as the area change of film, and the real-time stress response of drop impact. This study affords an innovative and promising track for multifunctional wearable sensors with wide applications in a harsh environment.