Bionic Superwetting Wedge-Shaped Surface for Rapid Long-Distance Self-Transport of Oil Droplets Underwater

The spontaneous and directional transport of liquids has significant application potential in microfluidics, biomedicine, microscale chemical reactions, etc. However, most of the current research focuses on the manipulation of water in the air, while the manipulation of oil in the aqueous environment remains a challenge. Herein, inspired by the groove structures of rice leaves and the spines of cacti, an underwater superwetting wedge-shaped surface was fabricated through femtosecond laser processing and chemical modification. This surface is composed of an internal superoleophilic wedge-shaped channel and a surrounding underwater superoleophobic background, enabling long-distance and directional self-transport of underwater-oil droplets. Additionally, USWS were prepared on aluminum alloy and copper surfaces using this method, enabling rapid, long-distance self-transport of oil droplets underwater. We discuss in detail the factors affecting the velocity of oil droplet movement, including volume, wedge-shaped angle, and viscosity of water. Furthermore, due to its excellent underwater-oil droplet self-transport performance, the fabricated USWS also achieves oil droplet manipulation on complex surfaces, including splitting, merging, and long-distance curves, as well as underwater-oil collection. This work provides new insights for designing high-performance underwater-oil droplet manipulation surfaces.