Durable Underwater Antifouling Coatings via Interfacial Engineering of Polyurethane Patches

Oil pollution, particularly from crude oil spills, poses considerable challenges to underwater equipment, increasing vessel resistance and affecting functionality. This study presents a polyurethane patch with interfacial activity (IAPU patch) that achieves underwater superoleophobicity and strong substrate adhesion. The IAPU patch is fabricated by molding a polyurethane precursor into films, which are then laminated onto epoxy resin-coated substrates. The epoxy–IAPU interfacial bond forms covalent linkages during lamination, ensuring robust adhesion. Upon water immersion, the patch swells into a hydrogel coating, creating a hydrated layer that repels oils with an underwater–oil contact angle (OCA) > 150° and a correspondingly low underwater–oil sliding angle (OSA) ≈ 5°. This IAPU coating has exceptional antifouling performance, as it inhibits bacterial adhesion (99.9% reduction in E. coli), protein adsorption (BSA (bovine serum albumin), Fg (fibrinogen)), and algae settlement. Mechanical durability is confirmed by resistance to water rinsing, sandpaper abrasion, and sonicating, with the underwater retraction of the OCA above 150° after damage. Controlled experiments revealed that the epoxy–polyurethane interfacial bond is critical for simultaneously achieving oil repellence and substrate adhesion. The scalable fabrication process enables large-area application, as demonstrated by coating a 30 × 30 cm stainless steel plate and shark models in oil-contaminated environments. This work presents a versatile platform for advanced marine coatings with combined antifouling, inhibition of bacterial adhesion, and anticlogging functionalities.