Binary Solvent-Induced Ultra-Adhesive Gel for Underwater Motion and Water Flow Detection

Hydrogel-based sensors face significant limitations due to swelling in aqueous environments, which compromises their mechanical integrity and distorts sensing signals, thereby hindering their widespread application. Here, a water-submersible hydrogel sensor capable of long-term underwater monitoring was prepared through highly cross-linked copolymerization of hydrophilic and hydrophobic monomers in a binary solvent system. Originating from the difference in affinity to the solvent, the hydrophobic polymers were prone to polymerize and wrap around to promote microphase separation, and the localized reinforced entanglement and cross-linking enabled the hydrogel excellent hydrophobic property, extremely strong antiswelling property (0.13% after 5 days), and impressive mechanical reinforcement. The underwater adhesive properties of the hydrogel were further enhanced by the synergistic effects of multiple physical and chemical interactions and a water-induced surface rearrangement, achieving a maximum adhesion strength of 54.4 kPa underwater. With abundant charged functional groups and dissociable salts, the hydrogel sensor demonstrated high sensitivity, rapid response time, and superior electromechanical stability in both air and underwater, enabling prolonged monitoring of underwater human activities and hydrological conditions.