Nanoscale Drag Reduction Effect Enables Efficient Fog Harvesting

Abstract Surfaces with macro‐scale hydrophilic/hydrophobic regions (conventional Janus mode) are often considered as prime candidates for fog harvesting. However, the water collection efficiency of such surfaces frequently fails to meet the requirements of practical applications due to the occurrence of surface flooding caused by water droplet pinning. Here, an in situ molecular confined modification strategy is proposed to construct upgraded Janus mode for achieving nanoscale drag reduction effect, thereby improving the fog collection efficiency. Specifically, nanoscale hydrophilic sites are designed to effectively reduce the critical volume size required for water droplets to slide off, thus avoiding the surface flooding. Fibers with upgraded Janus mode (PAN‐TO) realize a water collection rate of 4035 mg cm⁻² h⁻¹, markedly exceeding that of most materials with conventional Janus mode. Moreover, the high interface bonding strength between hydrophilic sites and the material surface can withstand the impact of water and sand flushing, ensuring the long‐term usability of the material. The applications of PAN‐TO fibers in irrigation and dyeing are demonstrated. This work shows a nanoscale surface engineering proposal for building a next‐generation fibrous fog harvesting device.