Underwater High Strength and Tough Polyvinyl Alcohol‐polyacrylic Acid Hydrogel

Abstract The mechanical properties of hydrogels always determine the reliability of relevant applications, and improving hydrogels’ mechanical properties is a hot topic in the hydrogel research field. The application range of hydrogels with excellent mechanical properties underwater will be more extensive. Synthetic hydrogels are created using methods such as double network (DN), dual cross‐linking, salting out, and mechanical stretching for improved mechanical performance. However, the synthetic hydrogels are often plagued by loose or inhomogeneous network structures. Herein, a strategy is presented to produce a dense and homogeneous network hydrogel. It introduces an energy dissipation mechanism by constructing a DN, followed by annealing to optimize the polymer network. The prepared hydrogel exhibits superb mechanical properties, including tensile strength (53.0 ± 5.0 MPa), fracture strain (1374 ± 104%), and toughness (315.7 ± 28.4 MJ m −3 ). Moreover, it can also exhibit similar mechanical properties underwater. Thanks to the conductive ions, the hydrogel is functionalized to have electrical conductivity. The hydrogel strain sensor can be used for real‐time monitoring of various joint movements of the human body, including finger, wrist, elbow, and knee. This work provides a new and effective strategy to fabricate strong and tough hydrogel with potential applications in intelligent flexible electronics.