Hierarchical structured surfaces enhance the contact angle of the hydrophobic (meta-stable) state

TL;DR

This paper presents a theoretical model and simulations demonstrating that hierarchical structured surfaces increase the contact angle of water droplets, with higher hierarchy levels enhancing metastability and contact angle, independent of fractal dimension.

Contribution

The study introduces a simple theoretical model linking hierarchical surface structures to wetting properties and uses simulations to explore metastability and contact angle behavior.

Findings

Higher hierarchy levels increase contact angle.

Metastability becomes more pronounced with increased hierarchy.

Fractal dimension does not predict contact angle.

Abstract

The relation between wetting properties and geometric parameters of fractal surfaces are widely discussed on the literature and, however, there are still divergences on this topic. Here we propose a simple theoretical model to describe the wetting properties of a droplet of water placed on a hierarchical structured surface and test the predictions of the model and the dependence of the droplet wetting state on the initial conditions using simulation of the 3-spin Potts model. We show that increasing the auto-similarity level of the hierarchy -- called $n$ -- does not affect considerably the stable wetting state of the droplet but increases its contact angle. Simulations also explicit the existence of metastable states on this type of surfaces and shows that, when $n$ increases, the metastability becomes more pronounced. Finally we show that the fractal dimension of the surface is not a good predictor of the contact angle of the droplet.