Self-healable and freeze-resistant polyelectrolyte based on an EG anchor chain and dual dynamic reversible interaction as highly sensitive ionic skin

Abstract

Presently, it is necessary to develop fully flexible sensors for the next generation of wearable electronics, and in this case, hydrogel-based flexible sensors are highly attractive due to their unique mechanical performances. However, the low-temperature freezing and bending fatigue of hydrogels severely hinder their application in flexible sensors. Herein, a polymeric dual-function hydrogel (DF-hydrogel) integrating self-healing and anti-freezing properties was prepared by building a dual dynamic network for application as ionic skin with excellent and reliable sensing performances. In DF-hydrogel, ethylene glycol (EG) and disulfide bonds were anchored in the molecular structure of double-bond-capped water-based polyurethane crosslinkers (DB-waPU) and subsequently introduced into the molecular backbone of the hydrogel via free radical polymerization. A multi-hydrogen bonding network was formed by the copolymerization of acrylamide with 2-ureido-4[1H]-pyrimidinone (UPy)-functionalized 1-vinylimidazole ionic liquid. Due to the dual dynamic network, DF-hydrogel exhibited exceptional self-healing capabilities and mechanical properties such as high healing efficiency, stretchability, compressibility, and self-adhesion. The anchored EG molecule in the polymer backbone endowed the hydrogel with intrinsic freeze-resistance without compromising its mechanical properties. The introduced poly(ionic liquid) provided free ions to the hydrogel, enhancing its ionic conductivity up to 9.6 mS cm⁻¹ in the absence of applied electrolyte salts. The DF-hydrogel-based ionic skins exhibited rapid, reversible, and dependable resistance changes with a wide range of strain sensing capabilities (10–300%). Moreover, a prototype 2D sensor array was fabricated to detect strains or pressures in two dimensions, strongly showing potential for the preparation of electronic skin, touch-pads, biosensors, and other applications.