Robust filmwise condensation for liquid collection*

Development of functional surfaces for liquid collection and their directional transport is of utmost importance to a variety of applications, such as industrial filtration processes, microfluidics/medical devices, water harvesting, and so on. Efficient liquid collection depends on how quickly the surface can transport the accumulated liquid to replenish the deposition process. To achieve higher droplet mobility, using superhydrophobic surfaces is quite common as they can induce dropwise condensation on a surface. However, on such surfaces pinning of droplets under high supersaturation might occur causing stagnation which limits their liquid-transporting capability. In this work, we present a robust, functional surface design that utilizes counter-intuitive filmwise condensation to achieve enhanced regulation of liquid deposition and transportation. The convex region of the surface enhances the deposition of liquid on the region by focusing the diffusion flux of vapor, while the omniphilicity and curvature of the surface initiates a Laplace pressure gradient along the surface curvature that results in quick transport of the deposited liquid from positive to negative curvature points. Furthermore, the proposed surface design is largely resistant to higher supersaturation, surface contamination, indentations and scratches. We analyze this robustness of the regulating mechanism by comparing the liquid collection rate subjected to varying amounts of surface contamination and wear.