Tunable\nWater Harvesting Surfaces Consisting of Biphilic\nNanoscale Topography

Abstract

Water scarcity has become a global\nissue of severe concern. Great\nefforts have been undertaken to develop low-cost and highly efficient\ncondensation strategies to relieve water shortages in arid regions.\nHowever, the rationale for design of an ideal condensing surface remains\nlacking due to the conflicting requirements for water nucleation and\ntransport. In this work, we demonstrate that a biphilic nanoscale\ntopography created by a scalable surface engineering method can achieve\nan ultraefficient water harvesting performance. With hydrophilic nanobumps\non top of a superhydrophobic substrate, this biphilic topography combines\nthe merits of biological surfaces with distinct wetting features (e.g.,\nfog-basking beetles and water-repellent lotus), which enables a tunable\nwater nucleation phenomenon, in contrast to the random condensation\nmode on their counterparts. By adjusting the contrasting wetting features,\nthe characteristic water nucleation spacing can be tuned to balance\nthe nucleation enhancement and water transport to cope with various\nenvironments. Guided by our nucleation density model, we show an optimal\nbiphilic topography by tuning the nanoscale hydrophilic structure\ndensity, which allows an ∼349% water collection rate and ∼184%\nheat transfer coefficient as compared to the state-of-the-art superhydrophobic\nsurface in a moisture-lacking atmosphere, offering a very promising\nstrategy for improving the efficiency of water harvesting in drought\nareas.