Drop Impact on Two-Tier Monostable Superrepellent Surfaces

Superrepellency is a favorable non-wetting scenario featuring a dramatic reduction of the solid/liquid contact area. The robustness of superhydrophobicity plays a central role in self-cleaning and anti-icing. Drop impacts happen ubiquitously in natural environments and often cause a notable extension of the solid/liquid contact area. This is associated with an enhanced affinity between water and the micro-textures and therefore leads to irreversible breakdowns in the superhydrophobicity. This problem remains a major challenge and limits the practical applications of superrepellent materials. In order to find a solution, in this paper, a repeated Cassie-Wenzel-Cassie wetting state transition is studied at the microscale when a drop impacts a two-tier superhydrophobic surface. In this case, the surface is completely dry without any liquid residue after the drop rebounds. The present results exhibit a striking contrast to the conventional perspective. The influence of geometrical parameters of the textured s...