Enhancement of coalescence-induced nanodroplet jumping on superhydrophobic surfaces with designed structures

The phenomenon of coalescence-induced droplet jumping on superhydrophobic surfaces has gained significant attention owing to its broad potential applications in self-cleaning, anti-icing, and phase-change heat transfer. In this study, molecular dynamics simulations were employed to investigate the coalescence-induced jumping behavior of nanodroplets on superhydrophobic surfaces with protruding, limitation, and combination structures. The simulations cover a broad range of parameters, including the dimensionless height of protruding structure (Hb* = 0–0.82), the dimensionless width (L* = 0.78–1.28), and the height (H* = 0–5) of the limitation structure, contact angles (100°–180°), and droplet radius ratios (0.6–1.3). The results reveal that all three patterned surfaces significantly influence droplet jumping behavior, with the specific effects depending on both structural parameters and droplet characteristics. Notably, the combination structure achieves the highest dimensionless droplet jumping velocity of 0.58 under specific conditions, corresponding to an energy conversion efficiency of 28.9%. This enhancement is attributed to the earlier impact of the expanding liquid bridge on the protruding structure and the increased asymmetry of the droplet morphology, along with the associated capillary force induced by the limitation structure during deformation. Additionally, the critical contact angles for coalescence-induced droplet jumping on superhydrophobic surfaces with flat, protruding, and combination structures are 162°, 117°, and 117°, respectively. It is also observed that the enhancement of droplet jumping is more pronounced for droplets of similar size.