Fabrication of long aliphatic chains (C18)-based adhesive with strong underwater adhesion strength

Conventional adhesives typically form strong and durable bonds only on dry surfaces, and their adhesion effectiveness often weakens or disappears entirely in the presence of water at the bonding interface. Thus, developing high-performance adhesives suitable for underwater applications is crucial. In this study, we successfully developed a high-strength (4.13 MPa) epoxy-based underwater adhesive (called MGEO) using a simple one-step, solvent-free strategy. After underwater adhesion, the adhesive rapidly transforms from liquid to solid at room temperature, forming a strong adhesion that requires no additional processing. The hydrophobic effect of the long aliphatic chain (C18) effectively facilitated water displacement at the interface, while multiple intermolecular interactions enhanced interfacial adhesion, ensuring strong and reliable underwater performance. Additionally, the adhesive exhibited excellent adhesive stability after it was immersed in different aqueous solutions for 20 d [alkali (3.39 MPa), salt (4.37 MPa), and artificial seawater (4.28 MPa)]. Moreover, the adhesive exhibited outstanding long-term stability in water and a strength of 3.87 MPa after 50 d of immersion. After the adhesive underwent 50 cold-hot shock cycles, it exhibited a strength of 3.59 MPa. After it underwent five underwater adhesion cycles, its strength was 2.29 MPa. The long-term durability of MGEO adhesive underwater demonstrates its excellent application potential in underwater repair.