Spontaneous Breakdown of Superhydrophobicity

TL;DR

This paper investigates the rapid and complex process of water wetting on micro-structured superhydrophobic surfaces, revealing different propagation modes and a novel stepwise wetting pattern through ultra-high-speed imaging.

Contribution

It provides a detailed analysis of the dynamics of spontaneous wetting breakdown on micro-structured surfaces, highlighting the stepwise 'zipping' mechanism and shape evolution.

Findings

Wetting fronts propagate smoothly or stepwise depending on micro-structure scale.

Stepwise wetting leads to a square-shaped wetted area.

The 'zipping' process occurs within microseconds.

Abstract

In some cases water droplets can completely wet micro-structured superhydrophobic surfaces. The {\it dynamics} of this rapid process is analyzed by ultra-high-speed imaging. Depending on the scales of the micro-structure, the wetting fronts propagate smoothly and circularly or -- more interestingly -- in a {\it stepwise} manner, leading to a growing {\it square-shaped} wetted area: entering a new row perpendicular to the direction of front propagation takes milliseconds, whereas once this has happened, the row itself fills in microseconds ({\it ``zipping''})