Janus membrane with heterogeneous wettability top surface for fog harvesting

To alleviate the global water scarcity crisis, fog harvesting has seen considerable development as a promising strategy. However, the current main challenge lies in achieving efficient fog deposition, timely transport of water droplets, and storage. Here, inspired by clusters of cactus trichomes and sponges, a Janus membrane with heterogeneous wettability top surface (JM-HWTS) is proposed. The JM-HWTS was obtained by spraying paraffin wax particles (hydrophobic) on the copper mesh top surface (superhydrophilic). The relationship between the loading amount of paraffin particles and the surface morphology, water permeability, and one-way penetration ability of the sample was clarified. Compared to fog collection surfaces with single hydrophilic or hydrophobic properties, the proposed JM-HWTS system significantly increased fog collection efficiency. For JM-HWTS, the fog will first deposit into water droplets on the hydrophobic front side, then grow up, and finally be sucked into the hydrophilic back side. This unique cyclic fog collection method is the key to efficient fog collection. The JM-HWTS exhibits excellent water-collection efficiency, enabling efficient capture of fog and rapid directional delivery of droplets. This work will significantly complement the fog collection and water droplet storage fields.