Binary collisions of equal-sized water nanodroplets: Molecular dynamics simulations

Abstract

Binary collision dynamics of equal-sized water nanodroplets are investigated numerically by using molecular dynamics (MD) simulations with a focus on the shape evolution and collision result of two colliding nanodroplets. The complete behavior of binary collisions is dynamically simulated using velocity-Verlet integrator in LAMMPS platform. Effects of several parameters such as impact velocity, dimensionless impact parameter (defined as the ratio of the off-center distance between the nanodroplets to the average diameter of two nanodroplets), liquid temperature and droplet size on binary collision outcomes are quantitatively studied. The simulations show that with the increasing of impact velocity, the outcome upon head-on binary collisions changes from coalescence to the fragmentation of the rim, and to disintegrates into many smaller nanodroplets. For impact parameter, the stretching separation is suppressed with the decrease of impact parameter. The controlling mechanism of stretching separation is basically related to the end-pinching mechanism dominated by high-inertia. For the higher liquid temperature, the liquid lamella caused by binary collisions leads to some tinier satellite nanodroplets because of the variations in thermophysical properties of fluid. The effect of larger nanodroplet diameter is found to enhance the deformation degree of head-on binary collisions. In addition, a We-B map map is established to qualitatively identify different regimes of binary collision. The present study provides some insight into the binary collision dynamics under micro-nano dimension for spraying engineering.