New insights into impact-induced removal of the deposited droplet

Abstract

This paper presents a comprehensive investigation into the collision dynamics of equal and unequal-sized nanodroplets on a flat surface using molecular dynamics simulations, revealing new insights into scaling laws and energy dissipation mechanisms. The simulations, conducted with the Large-Scale Atomic/Molecular Massively Parallel Simulator software, involved an initially stationary droplet on the surface and a suspended droplet with varying diameter ratios (λ) and impact velocities. The results show that at low Weber numbers (We < 24.15), the droplets tend to deposit after impact, while at higher Weber numbers (We ≥ 24.15), they undergo spreading and retraction, ultimately rebounding. The study reveals that the dimensionless contact time (t*) and maximum spreading factor (βmax*) in collisions between droplets of different sizes do not follow the same scaling relationship observed in single nanodroplet impacts. By redefining the Weber and Reynolds numbers (Re), the new scaling relationships t* ∼ We2/3Re−1/3λ−1/3 and βmax* ∼ We2/3Re−1/3λ−1/3 are proposed and validated. This work represents a further in-depth study of previous research on single nanodroplet impact, introducing for the first time the diameter ratio in unequal droplet impacts into the variation patterns of contact time and maximum spreading diameter. Moreover, these findings highlight the importance of revisiting and potentially revising classical theories to accommodate the unique physical phenomena that emerge at smaller scales.