Harnessing Water Molecules for Strong Underwater Adhesion

ABSTRACT Underwater adherable materials have attracted extensive attention due to their wide range of applications in marine exploration. However, current underwater adhesives still face a trade‐off between interfacial bonding and cohesive strength, limiting their underwater bonding performance. Herein, a water‐induced, toughening underwater adhesive to resolve the contradiction was reported, which can transform water molecules from barrier to reinforcement. The adhesive contains hydrophilic and hydrophobic units, which allow it to adaptively adhere to rough surfaces at as‐prepared soft state. Moreover, the strong interaction between polymer chains can be in situ activated by water molecules, leading to phase separation and enhancing mechanical properties of the adhesive in aqueous environments. This enables the adhesive to simultaneously achieve robust interfacial bonding and high energy dissipation during peeling. This strategy endows the adhesive with a high underwater interfacial toughness of 1602 ± 85 J m −2 . The adhesive is also transparent, recyclable, and long‐term stable. The underwater adhesion enhancement mechanism provides a new way to design underwater adhesive materials.