Droplet Impact Dynamics on Micropillared Hydrophobic Surfaces

TL;DR

This study investigates how the spacing of micropillars and impact velocity influence water droplet behavior on hydrophobic surfaces, revealing distinct bouncing regimes and wetting transitions through high-speed imaging and quantitative analysis.

Contribution

It introduces a novel characterization of transient impact dynamics and maps the regimes based on pitch and velocity, aligning with analytical models.

Findings

Identified three impact regimes: non-bouncing, complete bouncing, partial bouncing.

Discovered a critical pitch and velocity for regime transitions.

Demonstrated Cassie to Wenzel wetting transition at higher pitches and velocities.

Abstract

The effect of pitch of the pillars and impact velocity are studied for the impact dynamics of a microliter water droplet on a micropillared hydrophobic surface. The results are presented qualitatively by the high-speed photography and quantitatively by the temporal variation of wetted diameter and droplet height. A characterization of the transient quantitative results is a novel aspect of our work. Three distinct regimes, namely, non-bouncing, complete bouncing and partial bouncing are presented. A critical pitch as well as impact velocity exists for the transition from one regime to another. This is explained with a demonstration of Cassie to Wenzel wetting transition in which the liquid penetrates in the grooves between the pillars at larger pitch or impact velocity. The regimes are demarcated on a map of pitch and impact velocity. A good agreement is reported between the present measurements and published analytical models.