Liquid Collection on Welwitschia-Inspired Wavy Surfaces

Abstract: Hydrophobic (HPo) surfaces for atmospheric water harvesting applications require sophisticated wettability and microstructure patterns, which suffer from high cost and low durability against severe mechanical and environmental degradations. Inspired by the leaves of Welwitschia mirabilis, a long lifespan desert-living plant, we present a robust superhydrophilic (SHPi) surface design which is capable of enhancing both dew condensation and fog capture. The surface consists of a parallel-aligned millimetric wavy topography on top of which random nanostructures are grown. By studying the liquid dynamics, we have shown a unique mechanism of water transport on the SHPi wavy surface by droplet splitting and Laplace pressure gradient. It has been revealed that the efficient water transport on the SHPi wavy surface synergistically interacts with the enhanced diffusion flux of water vapor on the convex regions and significantly improves the efficiency of filmwise condensation. We have further demonstrated that wavy features enhance the probability of fog droplet collisions by disturbing the air flow and increasing the mean free path of fog droplets.