Highly compressible hydrogel sensors with synergistic long-lasting moisture, extreme temperature tolerance and strain-sensitivity properties

Abstract

With increasing interest and demand for wearable electronic skin sensors for human–machine interactions or personal health detection, fabricating a mechanically stiff, long-lasting moisture, high ionic conductivity, and extreme-temperature tolerant hydrogel electrolyte that maximally mimics the human skin is necessary, but remains a challenge. In this work, a dual-crosslinked hydrogel electrolyte was fabricated by simply immersing a photo-crosslinked polyvinyl alcohol (PVA-W) hydrogel into a tannic acid (TA)/NaCl/glycerin/H₂O solvent. The utilization of a glycerin/H₂O binary solvent not only significantly promotes the free diffusion of TA into the PVA-W hydrogel network, which could generate a high-mechanical-strength, homogeneous, and transparent hydrogel, but also effectively prevents the crystallization and evaporation of free water owing to the strong hydrogen bonding interactions. The constructed hydrogel electrolyte, named PT-GW, exhibits variable compressive stress from 0.37 to 9.85 MPa upon adjusting the TA concentration, and high compressibility and fatigue resistance over a wide temperature range from −20 to 60 °C, while retaining 90% of the original weight at 60 °C. The ionic conductivity of the PT100-GW hydrogel electrolyte retains a high value of 1.13 S m⁻¹ at 60 °C and 0.12 S m⁻¹ at −20 °C. Furthermore, this hydrogel sensor could precisely detect human joint motion and displays strain-dependence properties even in harsh environments. It is envisioned that this easily-prepared, low-cost and high-performance hydrogel electrolyte could a candidate for application in fields requiring multifunctional flexible electronic materials, such as biosensors, energy storage devices, and wearable devices.