Barnacle‐Inspired Underwater Adhesive with Instant, Robust, and Reversible Adhesion on Diverse Surfaces

Abstract Adhesion to wet surfaces and other harsh environments is of significant importance in various fields. However, developing instant and strong underwater adhesives for long‐term use still remains highly challenging. Herein, a novel adhesive (PUU‐FPD) that incorporates bulky hydrophobic “tentacles” and hydrophilic “anchors” within the network is reported inspired by the structure of barnacle cement proteins. The hydrophobic side chains can effectively remove bound water from the substrate surface through hydrophobic self‐assembly. Due to the hindrance of hydrophobic branches, the hydrophilic free urea/urethane groups in the protection area provide abundant hydrogen bonding bridges on the adhered surfaces, achieving instant and robust adhesion on various substrates (poly(methyl methacrylate), ceramic, steel, glass, polytetrafluoroethylene, and wood). The adhesive strength increases over time and reaches the maximum value (1.62 MPa) at ≈24 h. Remarkably, PUU‐FPD achieves stable adhesion under universal conditions, including extremely low temperatures (−196 °C), underwater, in salt water (35% NaCl solution), and in strong acid or alkaline environments (pH = 1 or 14). Based on dynamic hydrogen bonds, debonding‐rebonding of the adhesive can be recycled multiple times underwater. This underwater adhesive with excellent comprehensive performance offers an alternative material for practical applications, such as underwater sealants, electronic encapsulation, underwater devices, and repair.