Directional Droplet Transport Mediated by Circular Groove Arrays. Part II: Theory of Effect.

In the first part of this research, we reported the experimental study of the drop impact on the superhydrophobic circular groove arrays, which resulted in a directional droplet transport. In the second part, we further explored the influence of the Weber number (We), ridge height (H), and the deviation distance (r) between the impacting point and the center of curvature on the lateral offset distance (ΔL) of bouncing drops. The suggested theoretical analysis is in reasonable agreement with the experimental observations. We demonstrate that a Cassie-Wenzel wetting transition occurred within the microstructures of the relief under the threshold Weber number, for example, We ≅ 19-25, which switched the nature of drop bouncing. The dynamic pressure plays a decisive role in the directional droplet transport. The reported investigation may shed light on the solid-liquid interactions occurring on the patterned hierarchical surfaces and open up new opportunities for directional droplet transportation.