Hydrogen-Bonding-Crosslinked Polyzwitterionic Hydrogels with Extreme Stretchability, Ultralow Hysteresis, Self-adhesion, and Antifreezing Performance as Flexible Self-powered Electronic Devices

Abstract

Flexible strain sensors have received tremendous attention because of their potential applications as wearable sensing devices. However, the integration of key functions into a single sensor, such as high stretchability, low hysteresis, self-adhesion, and excellent antifreezing performance, remains an unmet challenge. In this respect, zwitterionic hydrogels have emerged as ideal material candidates for breaking through the above dilemma. The mechanical properties of most reported zwitterionic hydrogels, however, are relatively poor, significantly restricting their use under load-bearing conditions. Traditional improvement approaches often involve complex preparation processes, making large-scale production challenging. Additionally, zwitterionic hydrogels prepared with chemical crosslinkers are typically fragile and prone to irreversible deformation under large strains, resulting in the slow recovery of structure and function. To fundamentally enhance the mechanical properties of pure zwitterionic hydrogels, the most effective approach is the regulation of the chemical structure of zwitterionic monomers through a targeted design strategy. This study employed a novel zwitterionic monomer carboxybetaine urethane acrylate (CBUTA), which contained one urethane group and one carboxybetaine group on its side chain. Through the direct polymerization of ultrahigh concentration monomer solutions without adding any chemical crosslinker, we successfully developed pure zwitterionic supramolecular hydrogels with significantly enhanced mechanical properties, self-adhesive behavior, and antifreezing performance. Most importantly, the resultant zwitterionic hydrogels exhibited high tensile strength and toughness and displayed ultralow hysteresis under strain conditions up to 1100%. This outstanding performance was attributed to the unique liquid–liquid phase separation phenomenon induced by the ultrahigh concentration of CBUTA monomers in an aqueous solution, as well as the enhanced polymer chain entanglement and the strong hydrogen bonds between urethane groups on the side chains. The potential application of hydrogels in strain sensors and high-performance triboelectric nanogenerators was further explored. Overall, this work provides a promising strategy for developing pure zwitterionic hydrogels for flexible strain sensors and self-powered electronic devices.

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