Enhancement and Predictable Guidance of Coalescence-Induced\nDroplet Jumping on V‑Shaped Superhydrophobic Surfaces with\na Ridge

Coalescence-induced\ndroplet jumping has attracted significant attention\nin recent years. However, achieving a high jumping velocity while\npredictably regulating the jumping direction of the merged droplets\nby simple superhydrophobic structures remains a challenge. In this\nwork, a novel V-shaped superhydrophobic surface with a ridge is conceived\nfor enhanced and predictably guided coalescence-induced droplet jumping.\nBy conducting experiments and lattice Boltzmann simulations, it is\nfound that the presence of a ridge in the V-shaped superhydrophobic\nsurface can modify the fluid dynamics during the droplet coalescence\nprocess, resulting in a much higher droplet jumping velocity than\nthat achieved by the V-shaped superhydrophobic surface without a ridge.\nThe enhancement of the droplet jumping velocity is mainly attributed\nto the combined effect of the earlier and more sufficient impingement\nbetween the liquid bridge and the ridge, as well as the accelerated\ndroplet contraction by redirecting the internal liquid flow toward\nthe jumping direction. A high normalized jumping velocity of Vj*≈0.71 is achieved by the newly designed\nsurface,\nwith a 930% increase in the energy conversion efficiency in comparison\nwith that on a flat surface. Moreover, adjusting the opening direction\nof the V-groove at different groove angles is found to be an effective\nmethod to regulate the droplet jumping direction and expand the range\nof the jumping angle. Particularly, the droplet jumping angle can\nbe well predicted based on the rotational angle (ω) and the\ngroove angle (α), i.e., θ<sub>j,p</sub> ≈ 90°\n– 0.5α <i>–</i> ω.