Computation of the Wetting Properties of Randomly Structured Superhydrophobic Surfaces

Superhydrophobic surfaces are extremely non-wetting by virtue of their surface chemistry and roughness. Applications for them are being pursued in coatings, microfluidics, textiles, and other areas. Most analyses of the wetting of superhydrophobic surfaces have focused on pillar geometries. However, mass-produced superhydrophobic surfaces are likely to have random topologies. A computational model for the wetting of rough one-dimensional surfaces is described, and applied to random, self-affine surfaces with various levels of roughness and intrinsic contact angles. It is found that all wetting properties are generally controlled by the Wenzel roughness parameter r, even when drops are in the suspended Cassie state. Superhydrophobicity is attained above a threshold value of r. Similar results are also found for the wetting of dual-scale surfaces.