Underwater drag reduction via self-healing and robust air plastrons stabilized by candle soot-based coatings

In marine environments, the increased drag force on vehicles impedes their speed underwater, leading to high energy consumption and reduced vehicle efficiency. Superhydrophobic coatings have gained remarkable attention regarding drag reduction. Due to the collapse of the air plastron, the change from Cassie-Baxter to Wenzel state at high fluid impalement pressures, and various chemical conditions, these coatings lose their ability to reduce drag in cold marine settings. Candle soot nanoparticles are deposited into an elastic binder to create a strong, environmentally friendly porous superhydrophobic covering with healable plastron to solve these difficulties. The interconnected nano-pores of the soot particles retain the drag reduction performance by robustly maintaining the air plastron under water. The water droplets bouncing on elastic soot coating cause drag reduction by reducing their contact time. The soot-coated copper ball enfolds the gas cavity volume 14.83 times greater than that of the bare ball while impacting water. The near-zero drag coefficient values of the soot-coated copper sphere confirm its efficient drag reduction performance. In Taylor-Couette flow, the soot-coated rotor showed a 60% drag reduction as compared to the bare rotor. The rheological experiments showed a 15.26% reduction in the apparent viscosity of glycerol and a 13.86% shear stress reduction on soot coated surface at -10 °C. The soot-coated boat covered 31 cm more distance at high speed than the uncoated boat. The plastron of candle soot coating showed stability under lake water, pond waters, super-cold water, liquid nitrogen, acidic and basic media, artificial seawater, different organic solvents, and sand abrasion. Moreover, a soot-coated aluminium plate floated on the surface of water while bearing a load. The durability, passive plastron stability, and self-cleaning of candle soot superhydrophobic coating have the potential for efficient drag reduction and are suitable for large-scale applications even in arctic environments in order to improve the fuel efficiency and substantial energy savings.