Water‐Induced Phase Separation for Anti‐Swelling Hydrogel Adhesives in Underwater Soft Electronics

The development of hydrogel‐based underwater electronics has gained significant attention due to their flexibility and portability compared to conventional rigid devices. However, common hydrogels face challenges such as swelling and poor underwater adhesion, limiting their practicality in water environments. Here, a water‐induced phase separation strategy to fabricate hydrogels with enhanced anti‐swelling properties and underwater adhesion is presented. By leveraging the contrasting affinity of different polymer chains to water, a phase‐separated structure with rich hydrophobic and dilute hydrophilic polymer phases is achieved. This dual‐phase structure, meticulously characterized from the macroscopic to the nanoscale, confers the hydrogel network with augmented retractive elastic forces and facilitates efficient water drainage at the gel‐substrate interface. As a result, the hydrogel exhibits remarkable swelling resistance and long‐lasting adhesion to diverse substrates. Additionally, the integration of carboxylic multiwalled carbon nanotubes into the hydrogel system preserves its anti‐swelling and adhesion properties while imparting superior conductivity. The conductive phase‐separated hydrogel exhibited great potential in diverse underwater applications, including sensing, communication, and energy harvesting. This study elucidates a facile strategy for designing anti‐swelling underwater adhesives by leveraging the ambient solvent effect, which is expected to offer some insights for the development of next‐generation adhesive soft materials tailored for aqueous environments.