Droplet impact on asymmetric hydrophobic microstructures

TL;DR

This study investigates how water droplets impact asymmetric hydrophobic microstructures, revealing directional rebound behavior influenced by surface geometry and wetting properties, with implications for designing surfaces that control droplet movement.

Contribution

The paper provides new experimental and numerical insights into droplet impact dynamics on inclined microstructured surfaces, enhancing understanding of asymmetric wetting and rebound behavior.

Findings

Directional rebound occurs at high impact speeds.

Asymmetry is due to differential wetting of sidewalls.

Numerical simulations clarify droplet movement over pillars.

Abstract

Textured hydrophobic surfaces that repel liquid droplets unidirectionally are found in nature such as butterfly wings and ryegrass leaves and are also essential in technological processes such as self-cleaning and anti-icing. However, droplet impact on such surfaces is not fully understood. Here, we study, using a high-speed camera, droplet impact on surfaces with inclined micropillars. We observed directional rebound at high impact speeds on surfaces with dense arrays of pillars. We attribute this asymmetry to the difference in wetting behavior of the structure sidewalls, causing slower retraction of the contact line in the direction against the inclination compared to with the inclination. The experimental observations are complemented with numerical simulations to elucidate the detailed movement of the drops over the pillars. These insights improve our understanding of droplet impact on hydrophobic microstructures and may be a useful for designing structured surfaces for controlling droplet mobility.