Water condensation on a super-hydrophobic spike surface

Condensation-induced water drop growth was studied on a super-hydrophobic spike surface. The dynamics are described by three main stages depending on the size of the drop with respect to the different spike pattern length scales. The initial stage is characterized by nucleation of the drops at the bottom (cavities) of the spikes. During the intermediate stage, large drops are surrounded by smaller drops within the neighboring cavities in what is described as a "bright ring". This ring persists until coalescence occurs with the central drop. The last stage is characterized by Wenzel-type drops growing with scaling laws similar to that on a planar surface but with contact angle θ* ≈ 111°, lower than for deposited drops (θ = 164°). Condensation on spike surfaces does not retain anything of super-hydrophobicity, in contrast to super-hydrophobic square and strip patterns.