Tough, Transparent, and Wider-Temperature-Tolerant Deep Eutectic Hydrogels for Strain Sensing and Friction Nanogenerators

Abstract

Conductive hydrogels have shown significant potential in wearable flexible electronics; however, the ability to operate over wide temperature ranges remains challenging, not to mention the simultaneous incorporation of conductivity and mechanical robustness. Herein, a strategy to develop a poly(vinyl alcohol) (PVA)/poly(acrylic acid) deep eutectic hydrogel (PPDHA) based on a deep eutectic solvent (DES)/ water system through a two-step process of radical polymerization and freeze−thaw cross-linking is presented. Due to the synergistic effect of the DES/water system, solvent-induced microphase separation of PVA, ligand interaction between aluminum ions and carboxyl groups, multiple hydrogen bonding, and excellent performance of PPDHA, such as wider temperature tolerance (−60 to 50 °C), high conductivity (10.79 mS/ cm), excellent mechanical strength (1.08 MPa tensile strength; 6.82 MJ/ m 3 toughness; 1585% strain), and good transparency (over 80%), are achieved. Moreover, applications such as strain sensors based on the proposed PPDHA possessing high sensitivity over an ultrawide strain range (GF = 4.16 below 600%, 9.54 at 600−1200%, and 15.33 at 1200−1585%) and friction nanogenerators (TENGs) with PPDHA serving as electrodes illuminating 16 LEDs demonstrate that the proposed PPDHA hold great potential as candidates for wearable and self-powered electronics fields in extreme temperature environments.