Superhydrophobicity and Superhydrophilicity of Regular Nanopatterns

TLDR

The model topographies mimic the dimensional scale of natural structures that display comparable wetting behavior. Water droplet wetting and sliding on nanoasperities of controlled dimensions were experimentally examined. The hemi‑wicking theory accurately predicts advancing angles, and after silanization the patterns become superhydrophobic in line with Cassie‑Baxter and Wenzel models; a forest of hydrophilic/hydrophobic slender pillars is the most effective superwettable configuration, with edge shape and curvature critically influencing advancing angles.

Abstract

The hydrophilicity, hydrophobicity, and sliding behavior of water droplets on nanoasperities of controlled dimensions were investigated experimentally. We show that the "hemi-wicking" theory for hydrophilic SiO2 samples successfully predicts the experimental advancing angles and that the same patterns, after silanization, become superhydrophobic in agreement with the Cassie−Baxter and Wenzel theories. Our model topographies have the same dimensional scale of some naturally occurring structures that exhibit similar wetting properties. Our results confirm that a forest of hydrophilic/hydrophobic slender pillars is the most effective superwettable/water-repellent configuration. It is shown that the shape and curvature of the edges of the asperities play an important role in determining the advancing angles.