Impact of nanodroplets on solid spheres

Rising nanoscale technologies arouse interest in investigating the impact dynamics of nanodroplets. In this work, the impact of nanodroplets on solid spheres is investigated by the molecular dynamics simulation method, to comprehensively report outcome regimes and reveal the curvature effect, in wide ranges of Weber numbers (We) from 1.5 to 235.8, diameter ratios (λ) of nanodroplets to solid spheres from 0.3 to 5, and contact angles (θ) from 105° to 135°. Five outcomes are identified, including deposition, bouncing, splash, covering, and dripping. The former three outcomes are found in the high diameter ratio range (λ > 1), showing similar dynamic behaviors with impacts on flat surfaces, whereas in the low diameter ratio range (λ ≤)1, splash disappears, and covering and dripping take place additionally. At each contact angle, the outcomes are recorded in λ-We phase diagrams. It is found that the bouncing, splash, covering, and dripping are all promoted by decreasing diameter ratios; in addition, the critical Weber numbers for trigging bouncing and splash increase with decreasing θ. However, the critical We of the boundary between the bouncing to other regimes in the low diameter ratio range is not sensitive to wettability owing to the relatively small diameter of solid spheres. For quantitatively describing the curvature effect, the boundaries between the deposition and bouncing regimes in the high diameter ratio range and between the bouncing and other regimes in the low diameter ratio range are established. Both the established models show satisfactory agreement with the boundaries in the phase diagrams.