Wetting and Self-Cleaning Properties of Artificial Superhydrophobic Surfaces

TLDR

Some metal foils and leaf replicas feature two levels of roughening. The authors investigated wetting and self‑cleaning on silicon wafers with chemically hydrophobized spike arrays, leaf‑replica replicas, and fluorinated metal foils. Silicon samples with slender spikes and narrow pitches roll off droplets and can be cleaned by fog, whereas surfaces lacking sub‑5 µm structures or with dual roughening levels require kinetic impact to achieve complete cleaning, and fog alone fails to remove particles from such surfaces.

Abstract

The wetting and the self-cleaning properties (the latter is often called the "Lotus-Effect") of three types of superhydrophobic surfaces have been investigated: silicon wafer specimens with different regular arrays of spikes hydrophobized by chemical treatment, replicates of water-repellent leaves of plants, and commercially available metal foils which were additionally hydrophobized by means of a fluorinated agent. Water droplets rolled off easily from those silicon samples which had a microstructure consisting of rather slender spikes with narrow pitches. Such samples could be cleaned almost completely from artificial particulate contaminations by a fog consisting of water droplets (diameter range, 8-20 microm). Some metal foils and some replicates had two levels of roughening. Because of this, a complete removal of all particles was not possible using artificial fog. However, water drops with some amount of kinetic impact energy were able to clean these surfaces perfectly. A substrate where pronounced structures in the range below 5 microm were lacking could not be cleaned by means of fog because this treatment resulted in a continuous water film on the samples.