Numerical study of energetics and wetting stability of liquid droplets on microtextured surfaces

Abstract

The suspended wetting state (Cassie-Baxter state) on a microstructured surface tends to collapse to a wetted state (Wenzel state) if the liquid-air interface is perturbed. Multiple metastable Cassie-Baxter (CB) wetting states, separated by an energy barrier from Wenzel state, may also exist. In this study, numerical method is applied to study the wetting properties of liquid droplets on a variety of microtextured surfaces with a particular focus on the stability of the CB wetting state. A dimensionless form of droplet energy is used to compare the relative stabilities of multiple metastable states. The sequence of stable drop configurations with increasing droplet volume on a particular substrate is analyzed for both isotropic and anisotropic cases. Applying dimensional variation, characterized by the pillar spacing and pillar width, on surface microtexture, the key parameter which plays dominant role in the stability of droplet is explored. The solid-fraction that the droplet avails at the drop-base is observed to be the most vital parameter for the droplet stability. Spreading of droplet from one isotropic wetting configuration to an anisotropic configuration is not favorable unless the spreading of the droplet is restricted to be unidirectional.