Droplet impact on nano-textured bumps: Topology effects

Using the lattice Boltzmann method (LBM), the dynamics of a single droplet impacting on desert-beetle inspired, super-hydrophobic, nano-textured bumps was numerically investigated. The focus was placed on the effects of post height, inter-post spacing, bump radius of curvature and impact velocity represented by the Weber number. Three droplet states after the impact were captured, i.e., the suspended Cassie state, the sticky Wenzel state and rebound. The interfaces among these states were then determined in parametric maps generated from the current study. Since the droplets in the Cassie state can be easily removed from the surface and thus favorable for water collection. The conditions satisfied for this state by the geometrical parameters and the Weber number were explored. The results showed that, at moderate impact speeds, droplets impacting on nano-textured bumps with sufficiently high posts or sufficiently small inter-post spacing were generally in the Cassie state and hence favorable for water collection. If these conditions are satisfied, the bump surface curvature only plays a marginal role.