Cation‐π‐Driven Responsive Underwater Adhesives with High Adhesion Switching Ratios

Abstract Stimuli‐responsive underwater adhesives capable of dynamically modulating adhesion strength offer significant potential for diverse applications. However, achieving robust adhesion coupled with facile detachment remains a major challenge. Here, pH‐responsive underwater adhesives are presented exhibiting an ultrahigh adhesion switching ratio of ≈8471 by leveraging tunable cation‐π interactions between polyethyleneimine‐derived amino cations and catechol aromatic moieties. This adhesive demonstrates responsive adhesion modulation through pH‐controlled phase transitions between weakly adhesive coacervates (≈0.00017 MPa at pH 8.5) and strongly adhesive gums (≈1.44 MPa at pH 10.5). The pH‐dependent protonation equilibrium governs the strength of cation‐π interactions, as quantified by their binding energies, thereby regulating the dynamic cross‐linked network and underwater adhesion strength over a wide range. The gum phase exhibits superior viscoelasticity intermediate between conventional glues and pressure‐sensitive tapes, enabling shape‐adaptive sealing of complex geometries underwater. Notably, the adhesive demonstrates exceptional recyclability through freeze‐drying/rehydration cycles, maintaining its initial adhesion efficiency after multiple regenerations. Post‐adhesion oxidative cross‐linking further enhances interfacial adhesion to ≈4.42 MPa through covalent reinforcement of the dynamic network. This study provides fundamental insights for designing smart adhesives for intelligent underwater applications.