Biomimetic underwater adhesives based on IL-mediated coacervation.

Developing highly efficient underwater adhesives is crucial in the fields of marine engineering and soft electronics. However, it is challenging to develop glues with integration of rapid solidification, robust adhesion, durability in diverse environments and conductivity. Herein, inspired by mussel proteins, a coacervation-derived glue was synthesized based on histidine and tryptophan mimetic polymers and ionic liquids (ILs). Key motifs of benzene, imidazole and benzotriazolium, were integrated into the polymer, which promoted the water-driven coacervation by forming multiple physical interactions. The effect of the IL structure on coacervation and underwater adhesion was studied. Instant coacervation was achieved by using ILs with suitable hydrophilicity, which can promote the exchange degree of ILs and surrounding water; meanwhile, suitable rheological behavior and robust underwater adhesion were realized by precisely regulating the affinity of ILs to polymers. The glue was effective for diverse surfaces and in various environments, including in saline water (1 M NaCl), acidic solution (pH = 3), and alkaline solution (pH = 12). Benefiting from the residual ILs, the solidified adhesive exhibited anti-freezing and conductive properties, and not only showed robust adhesion at sub-zero temperature (-40 °C) but can also sense the applied strain at the adhesion point. This work should provide new insights into the design of coacervation-derived adhesives.