Dynamic behaviors of nanoscale binary water droplets simultaneously impacting on flat surface

Abstract

Dynamic wetting of nanoscale binary water droplets simultaneously impacting on flat copper surface is explored using molecular dynamics simulations (MDS). The spreading performance is described through the images of shape evolution and the temporal variations of radial spreading factor and dynamic contact angle. The corresponding spreading characteristic is separately assessed by the following five key aspects: impact velocity, impact direction, the potential depth between oxygen and surface atoms, the center distance of binary nanodroplets and nanodroplet diameter, respectively. Here, the simulated results show that the binary nanodroplets with a low impact velocity exhibit the advancing, receding and coalescing motion states and the fluid with the high impact speed spreading on the solid surface may develop into jet flow along the radial direction. For impact direction, the radial momentum will cause larger axial wetting length with the increase of impact angle. In addition, a wide motion regions of binary water droplets impingement from partial wetting to non-wetting are observed, which helps us better understand the feature of nanodroplet equilibrium. Besides, the influence of coupling strength on dynamics behavior is also considered. We find that the center distance of binary droplets is relatively small, which will be conducive to the jetting occurrence. The enhancement of momentum and mass transport of the colliding two equal-sized nanodroplets also boosts the jetting as the droplet diameter increases.