Asymmetric Interfacial Dynamics during Oblique Impact of Two Unequal-Sized Nanodroplets on Superhydrophobic Surfaces

Molecular-level understanding of droplet rebound on nonwetting surfaces is important for controlling liquid transport and removal. In this work, molecular dynamics simulations are used to investigate the oblique impact of two unequal-sized nanodroplets on a superhydrophobic Pt surface. The effects of Weber number and inclination angle on impact morphology, spreading, rebound, and energy dissipation are systematically examined. With increasing Weber number, the impact outcome evolves from regular deposition to regular bouncing, hole bouncing, and breakup-dominated states. Increasing the inclination angle enhances tangential momentum and impact asymmetry, thereby promoting perforation and fragmentation while reducing the maximum spreading factor. An inclination-corrected scaling relation, We^0.382Re^0.411 sinα^-0.365, better describes the spreading behavior than conventional inclination-independent correlations. Rebound analysis shows that the inclination angle regulates horizontal displacement, restitution coefficient, takeoff velocity, and contact time by altering momentum partition and asymmetric recoil. Energy analysis further indicates that although viscous dissipation increases with Weber number, its proportion relative to the initial kinetic energy decreases. More importantly, the coupling between oblique impact and droplet-size asymmetry activates a rolling-assisted rebound mode, providing an additional route for energy redistribution. These results reveal how dynamic and geometric asymmetries govern nanodroplet mobility on superhydrophobic surfaces.