Modeling an impact droplet on a pair of pillars

Abstract

In this work, we use a multiphase lattice Boltzmann algorithm to simulate the impact of a droplet on a surface with a pair of pillars. The expected equilibrium wetting states of a droplet on a textured superhydrophobic surface normally are the Wenzel or the Cassie-Baxter state. An extra wetting regime arises when considering the wetting of a pair of pillars where the droplet wets both sides of the pillars but an air pocket appears directly under the droplet in the spacing between the two pillars. This wetting outcome is henceforth referred to as the engulfed state. Also, the effect of important control parameters such as geometrical parameters on creating the engulfed state is studied. We propose a regime map for different Weber numbers and geometrical parameters to predict the whole range of possible wetting states which are the engulfed, Wenzel, Cassie-Baxter, and breakup states. Finally, the influence of patterned substrates wettability on outcomes is investigated. Results show that the wetting state varies as the equilibrium contact angle changes from 60° to 150°.