Impact states and energy dissipation in bouncing and non-bouncing droplets

Abstract

Superhydrophobic surfaces made up of an array of micron-scale posts are importantcandidates for a wide range of applications in microfluidics. The feasibility of such surfacesis, however, limited by the fact that the more useful partially wetting Cassie–Baxter stateis often metastable compared to the complete wetting Wenzel state. We study thetransitions between these two states in droplet impact by means of computer simulationsusing a two-phase lattice Boltzmann model. Depending on the impact velocity, the dropletmay bounce off the surface or land on the surface in different wetting states. Inorder to better understand the factors affecting these different behaviours, weanalyse the energy dissipation in the droplet impact and find that, when liquidis withdrawn from in between the posts, strong dissipation occurs. Thus, thenumber of posts impaling the droplet has a significant effect on the observed impactregime.