Freezing-Melting Mediated Dewetting Transition for Droplets on Superhydrophobic Surfaces with Condensation.

The water-repellence properties of superhydrophobic surfaces make them promising for many applications. However, in some extreme environments, such as high humidities and low temperatures, condensation on the surface is inevitable, which induces the loss of surface superhydrophobicity. In this study, we propose a freezing-melting strategy to achieve the dewetting transition from the Wenzel state to the Cassie-Baxter state. It requires freezing the droplet by reducing the substrate temperature and then melting the droplet by heating the substrate. The condensation-induced wetting transition from the Cassie-Baxter state to the Wenzel state is analyzed first. Two kinds of superhydrophobic surfaces, i.e., single-scale nanostructured superhydrophobic surface and hierarchical-scale micronanostructured superhydrophobic surface, are compared and their effects on the static contact states and impact processes of droplets are analyzed. The mechanism for the dewetting transition is analyzed by exploring the differences in the micro/nanostructures of the surfaces, and it is attributed to the unique structure and strength of the superhydrophobic surface. These findings will enrich our understanding of the droplet-surface interaction involving phase changes and have great application prospects for the design of superhydrophobic surfaces.