Analysis of the energetics and stability of liquid droplets on textured surfaces with square micropillars

Abstract

Numerous studies have established that roughening a hydrophobic surface can induce superhydrophobic properties on that surface. The suspended wetting state (Cassie-Baxter state) on a microtextured surface tends to collapse to a wetted state (Wenzel state) due to external stimulations. Multiple metastable Cassie-Baxter wetting state, separated by an energy barrier from Wenzel state, may also exist. In this study, 3D droplet models are developed to numerically investigate the shapes and energies of CB droplets residing on rough surfaces patterned with square pillars. A normalized form of droplet energy is used to compare the relative stabilities of metastable states. The sequence of stable droplet configurations with increasing droplet volume is analyzed for different isotropic wetting cases. Analysis reveals that wetting configuration with the most number of pillars at the drop-base suspends the biggest with higher stability compared to other configurations . In order to explore droplet energetics on distinct substrates, the pillar width and spacing are varied in simulations. For the the same drop-base area, the substrate that gives the least value of solid-fraction at the drop-base, characterized by its pillar width and spacing, suspends the biggest droplet as the most stable CB droplet compared to others.