Critical conditions for whether two impacting nanodroplets can coalesce or not: a molecular simulation study

Molecular dynamics simulations are carried out to study impact-induced coalescence behaviors for the first time. When the droplets possess different impact velocities, the big difference between them could induce unconventional coalescence behaviors that exhibit non-synchronous spreading and retraction processes, and thus produce non-coalescence behaviors. At the same impact velocity, the distance of two impacting droplets plays a vital role in their coalescing dynamics. We here present the lower and upper critical values of distance in a map to determine whether two droplets after impacting can coalesce or not, which are highly dependent on the impact velocity. Moreover, simulation studies show that the upper critical value is 2(R-max - R), while the lower critical distance increases with the increase of impact velocity. This work not only helps advance our understanding of the effect of impact dynamics on the coalescence behaviors, but also shows the critical conditions for coalescence and non-coalescence behaviors, which could be considered as a new strategy to control the coalescence by tuning the impact parameters, and are expected to be used for some potential applications.