Wetting Transitions of Condensed Droplets on Superhydrophobic Surfaces with Two-Tier Roughness

TL;DR

This paper investigates spontaneous wetting transitions of condensed droplets on superhydrophobic surfaces with two-tier roughness, revealing a size-dependent transition mechanism and three distinct wetting modes that enhance water removal.

Contribution

It introduces a theoretical scaling law linking droplet size to micropillar spacing, explaining the wetting transition phenomenon on superhydrophobic surfaces.

Findings

Wetting transitions occur spontaneously when droplet size matches micropillar scale.

Three distinct wetting transition modes are identified and characterized.

Smaller micropillar spacing significantly improves water removal efficiency.

Abstract

Although realizing wetting transitions of droplets spontaneously on solid rough surfaces is quite challenging, it is becoming a key research topic in many practical applications which require highly efficient removal of liquid. We report wetting transitions of condensed droplets occurring spontaneously on pillared surfaces with two-tier roughness owing to excellent superhydrophobicity. The phenomenon results from further decreased Laplace pressure on the top side of the individual droplet when its size becomes comparable to the scale of the micropillars, which leads to a surprising robust spontaneous wetting transition, from valleys to tops of the pillars. A simple scaling law is derived theoretically, which demonstrates that the critical size of the droplet is determined by the space of the micropillars. For this reason, highly efficient removal of water benefits greatly from smaller micropillar space. Furthermore, three wetting transition modes exist, in which the in situ wetting behaviors are in good agreement with our quantitative theoretical analysis.