Bio-inspired hairy wires for fog collection*

Water collection from fog in the atmosphere can be a promising solution to water scarcity in many regions around the world. Commercial fog harvesters using mesh structures composed of cylindrical wires with a certain permeability, have a limited fog collection efficiency due to the following trade-off problem. Specifically, micrometric airborne fog droplets pass through a permeable mesh with less deposition on the wire surfaces as the wire diameter increases, resulting in low deposition efficiency. Conversely, meshes with thinner cylinders tend to clog, exhibiting lower drainage efficiency. To overcome this trade-off, we propose a bio-inspired hierarchical structure that includes a vertical core surrounded by multiple thin hairs protruding radially, which can greatly enhance both deposition and drainage efficiencies. The thin hairs allow fog droplets to make contact with the structure and deposit on the hair surfaces efficiently, while the vertical core wires facilitate the rapid drainage of deposited droplets through a wicking mechanism. The hierarchical hairy wires can achieve a steady-state water collection rate up to three times as high as that of cylindrical wires of the same outer diameter, and their excellent performance does not degrade, a common issue with conventional meshes composed of thin wires. We envision that this study offers a new way to design fog collectors with improved water collection efficiency, contributing to solving the global water crisis.