Ultraviolet- and Microwave-Protecting, Self-Cleaning e-Skin for Efficient Energy Harvesting and Tactile Mechanosensing.

Abstract

Smart, self-powered, and wearable e-skin that mimics the pressure sensing property of the human skin is indispensable to boost up cutting edge robotics, artificial intelligence, prosthesis, and health-care monitoring technologies. Here, fabrication of a facile and flexible hybrid piezoelectric e-skin (HPES) with multifunctions of tactile mechanosensing, energy harvesting, self-cleaning, ultraviolet (UV)-protecting, and microwave shielding properties is reported. The principal block of the HPES is an SnO2 nanosheets@SiO2 (silica-encapsulated tin oxide nanosheets)/poly(vinylidene fluoride) (PVDF) nanocomposite (SS)-based PES acting as a single unit for simultaneous energy harvesting and tactile mechanosensing. Gentle human finger imparting onto the PES showed outstanding energy conversion efficiency (16.7%) with high power density (550 W·m-3) and current density (0.40 μA·cm-2). This device can generate high enough electrical power to directly drive portable electronics like a light-emitting diode (LED) panel (consisting of 85 commercial LEDs) and to charge up capacitors very rapidly. Thin PES mechanosensors demonstrated promising performance for quantitatively detecting static and dynamic pressure stimuli with a high sensitivity of 0.99 V·kPa-1 and a short response time of 1 ms. PES was also integrated to a health-data glove for precisely monitoring and discriminating fine motions of proximal interphalangeal, metacarpophalangeal, and distal interphalangeal joints of a human finger and bending motion of different human fingers. A (4 × 4) sensing matrix of PES was successfully employed to detect the spatial distribution of static pressure stimuli. The sensing matrix can precisely record the shape and size of an object placed onto it. PES was encapsulated with a nanocomposite film for providing self-cleaning and UV and microwave protection capability to the HPES. The hydrophobic SS film wrapping (water drop contact angle ∼85.6°) of the HPES enables the self-cleaning feature and makes HPES resistive against water and dirt. The HPES was integrated with in-house-made robotic hands, and the responses of the sensors due to grabbing of an object were evaluated. This work explores new prospects for UV- and microwave-protective, self-cleaning e-skin for energy harvesting and mechanosensation, which can eventually boost up the self-powered electronics, robotics, real-time health-care monitoring, and artificial intelligence technologies.