Directional Metastable Wetting Evolution of Droplets on Artificial Patterned Microcavity Surfaces

Controllable wetting transition on artificial microtextured surfaces has significant applications in many industrial fields. In this work, the droplet spreading and the directional wetting transition are investigated on the substrate surface with the patterned microcavities. The results show that the macroscopic inward wetting transition from the periphery to the center of the droplet strongly depends on the mesoscopic sequential transition from Cassie to Wenzel state in the microcavities on the substrate surfaces. The semiquantitative relationship between sagging depth of meniscus in the microcavities and the droplet spreading velocity is set up by utilizing scaling-law analysis in terms of mechanical equilibrium of the meniscus. This finding is expected to help to clarify the issues on the mechanism and main affecting factors of the wetting transition on the patterned surface.