Catapulting impacting droplets via a wettability-patterned metal mesh

A water droplet striking orthogonally a superhydrophobic metal mesh may partially penetrate the mesh if the stagnation pressure is greater than the breakthrough pressure. On the other hand, the same droplet impacting a superhydrophilic mesh tends to stick to the wires due to the high pinning force. In the present work, experimental observations of droplet impact on wettability-patterned metal meshes are presented. The droplet impacts on the contrast line separating a semi-infinite superhydrophobic domain from a superhydrophilic counterpart. It is observed that, upon impact, a part of the droplet penetrates through the superhydrophobic side, while the liquid impacting the superhydrophilic side gets pinned. This pinning phenomenon forces the rest of the droplet on the superhydrophobic side, that undergoes rebound upon impact, to be vectored toward the superhydrophilic side. For a specific range of droplet diameter and pore size of the mesh, the momentum of the vectoring portion may be so large that a part of it breaks away and is launched in a lateral direction, akin to a projectile. The physical processes responsible for such a motion are identified, and a regime map is presented that separates the different types of post-impact behaviors observed in the experiments.