Bilayer PVA composite film with structural color for high-performance and multifunctional sensing

Intelligent E-skins attract lots of attention for their potential in health monitoring, human-computer interaction, and soft-body robotics. In this work, a colorful multifunctional E-skin sensor with a Janus structure was constructed by solution casting of polyvinyl alcohol (PVA) with clay and carbon nanoparticles on a patterned PDMS template. The halloysite nanotubes (HNTs) and carbon nanoparticles (C) derived from Chinese ink were introduced into PVA to obtain a nano-reinforced layer (top) with structural color and multi-functional layer (bottom) for detection of pressure, temperature, and humidity. Uniformly dispersed HNTs greatly improves the mechanical properties of PVA (up to 46.8 MPa at 303.9% strain). The difference in water absorption of the two layers provides excellent sensitivity to humidity, so it can be used as contactless password unlocking, closing and blooming of bionic flowers, and humidity alarm. The device can achieve object capture and release within 12 s by turning on and off the xenon light. Furthermore, the sensor responds distinctly to pressure and can track human activities such as drinking motion and finger bending, which can also detect the temperature by resistance change. This work provides a materials design strategy for E-skin aimed to applications in robotics, artificial intelligence, prosthetics, and health monitoring.