Bouncing dynamics of impacting unequal-sized sessile droplets: An atom-level study

The dynamic behavior of nanodroplets impacting unequal-sized sessile droplets has a wide range of applications in engineering, including anti-erosion, anti-icing, and self-cleaning. This study employs molecular dynamics simulation to investigate the dynamic behavior of a nanodroplet impacting another unequal-sized sessile droplet. The time evolutions of the spreading factors are used to analyze the particular dynamic behaviors and elucidate the underlying physics. A new extended scaling law βmax ∼ ηWe1/2Re1/5 characterizes the relationship between the maximum spreading radius βmax and the ratio of droplet radius η, Weber number We, and Reynolds number Re. The ratio of the contact time of unequal-sized droplet impact to that of a single droplet impact decreases with the increase in η, with a slope of −1/2 when η 1 and −20/7 when η 1. The two conditions intersect at 1.414 when η = 1, representing equal-sized droplet-on-droplet impact, which agrees with previous macro-scale droplet impact studies. Two boundaries are identified to discriminate among three outcomes: deposition, bouncing, and splashing, which are highly dependent on both the impacting velocities and the ratio of droplet radius. The conclusion of this article can lay a theoretical foundation for effectively manipulating nanoscale droplets. The research findings can provide theoretical guidance for engineering fields such as anti-icing coating design, micro-droplet printing, and spray cooling.