Water-Induced Ion-Responsive Phase Separation Enables Energy-Dissipative Ionogels for Robust Underwater Adhesion

The intrinsic trade-off between interfacial compliance and cohesive strength remains a central challenge in the design of high-performance self-adhesive soft materials, particularly in aqueous and saline environments where interfacial water impedes intimate contact and ions alter network cohesion. Here, we report a water-induced, ion-responsive phase-separation strategy for developing energy-dissipative ionogel adhesives with robust underwater adhesion. The as-prepared ionogel forms a homogeneous and compliant network that readily adapts to rough submerged substrates, promoting conformal interfacial contact. Upon water infiltration, the ionogel undergoes controlled phase separation, generating polymer-dense domains that serve as dynamic energy-dissipating structures and substantially reinforce the cohesive network. As a result, the underwater adhesive strength increases by up to 15-fold after equilibration in deionized water, while further enhancement is achieved in saline environments. Intermolecular force measurements and molecular dynamics simulations reveal that salinity-mediated electrostatic screening promotes short-range attractive interactions and stabilizes polymer-dense domains, thereby strengthening polymer-polymer association and enhancing interfacial toughness. By contrast, K+ weakens cohesion by disrupting cation-π interactions, revealing pronounced ion-specific regulation of phase behavior and adhesive performance. The resulting ionogel integrates strong underwater adhesion, high toughness, and ionic conductivity, enabling potential applications in underwater repair, in situ sensing, and signal communication. This work establishes water-induced, ion-responsive phase separation as a general molecular design principle for overcoming the compliance-cohesion trade-off in functional soft adhesives operating in complex aqueous environments.