Tailored Hierarchical Bonding Networks Derive Ultra‐Stable Underwater Adhesion in Harsh Environments

Abstract The development of high‐performance water‐resistant and underwater adhesives is critical for advancing underwater technologies, yet achieving robust functional adhesion with long‐term durability in complex underwater environments remains a significant challenge. Here, we present a hierarchical bonding network strategy to realize stable adhesion under harsh underwater conditions. By engineering a cross‐linked polysiloxane backbone embedded with dense active interaction sites, including hydroxyl groups, benzene rings, cations, and hydrophobic moieties, we create synergistic multiscale interactions that amplify both cohesion and interfacial adhesion. The optimized adhesive achieves a strong bonding strength of 12.2 MPa and an underwater adhesion of 3.4 MPa on steel substrates and retains stability in corrosive underwater environments (acidic, alkaline, and saline solutions) over extended periods. It further demonstrates exceptional thermal resilience, maintaining functionality across temperatures from ‐196 to 150 °C. Integrating quaternary ammonium cations with long‐chain alkanes endows the material with potent antibacterial activity (≥99.9999% inhibition) and the highest antifungal grade. This work provides a new avenue for designing high‐performance multifunctional adhesives with strong adhesion, long‐term durability, extreme temperature resistance, and antimicrobial properties, offering broad potential for applications in demanding underwater environments.