Directional water-collecting behavior of pine needle surface

Collecting water from dew, foggy wind or moisture present in the air recently has been recognized as a method to solve water shortage. In this paper, the directional fog harvesting ability of the pine needles is investigated. Results show that water droplets deposited on the surface of the pine needles can spontaneously move toward the root along the microchannel formed by the groove structure under the Laplace pressure generated by the shape gradient. This process is underpinned by the wettability gradient present on the surface. Inspired by the directional water-catching ability of pine needles, a pine-needle-like structure was constructed to achieve efficient fog harvesting without applying any external force.