Osthole-infused polyurethane flexible coatings for enhanced underwater drag reduction and robust anti-biofouling

Excessive underwater drag, coupled with a heavy marine fouling, not only adversely affects the operation and speed of ships but also leads to increased energy and fuel consumption. Inspired by the remarkable drag reduction and anti-biofouling capabilities of dolphin skin, we have developed a flexible polyurethane (PU) coating infused with osthole (OST). This coating not only exhibits exceptional drag reduction by postponing the boundary layer transition from laminar to turbulent flow but also demonstrates robust anti-biofouling properties under both dynamic and static scenarios. The resultant PUx/OSTy composite coating achieved the drag reduction efficiency of 8.20 % to 12.65 % with mean flow velocities ranging from 1 to 6 m/s. The PUx/OSTy surfaces also displayed highly enhanced anti-biofouling performances, with ∼98.4 % and 97.5 % reduction for green algae Chlorella and the diatom N. closterium, respectively, as well as ∼99.4 % reduction against P. pantotrophus. Furthermore, the PUx/OSTy coating had amazing durability in extreme environments, such as light aging, cycle sand abrasion, thermal aging, ultrasonic treatment, and tape-peeling. Therefore, this study underscores the potential of the bioinspired flexible coating for the application of underwater devices with prominent drag reduction and antifouling performance.