Water-induced phase separation enables underwater adhesion far exceeding dry adhesion

Underwater adhesion is crucial for repair work, marine industry, and water-based energy devices. However, water, which hinders close contact between the adhesive and adherend, also weakens cohesion, resulting in weak underwater adhesion strength, typically less than 1 MPa. Ingeniously, owing to the formation of a special interfacial phase structure induced by water, the underwater adhesion strength dramatically surpasses that of dry adhesion, with unprecedented 12.19 MPa in this work, exceeding those of underwater adhesives reported so far. This excellent adhesion performance is attributed to the surface anchoring effect of nanoparticles formed <i>in situ</i> from the local precipitation of the hydrophobic elastomer in the glue induced by water. Successful detachment of a nano-thickness interfacial bond layer from the adhesive by focused ion beam enables clear characterization for the nanoparticle structure using high-resolution transmission electron microscopy. Microscopic characterization reveals the mechanism behind the enhanced adhesion, leveraging which, strong adhesion to various substrates including metal, plastic, glass amid water, acid, alkali, oil, and artificial seawater has been realized. Our study provides a universal strategy for robust adhesion through the formation of a special interfacial phase structure induced by the liquid medium.