Molecular Dynamics Simulations of Thermo-Mechanical Effects in Nanodrop Impact

Nanodrop impact onto a solid substrate is of interest for nano-scale liquid-impingement, phase-change cooling and for material deposition processes. In the present study, classical molecular dynamics (MD) simulation techniques were implemented to study the thermo-mechanical properties of the impact of nanometer scale liquid droplets upon an atomistic substrate at a temperature higher than that of the droplet. The droplets were comprised of approximately 50,000 Lennard-Jones atoms arranged in tetramer finitely extensible non-linear elastic (FENE) chain molecules forming a sphere of 8 nm radius. They were equilibrated and then projected towards a wall, where we observed the response upon collision by changes in shape, temperature, and density gradients, across a variety of impingement velocities, substrate temperatures, and wetting conditions. The baseline cases of equal substrate and nano-drop temperature were validated by comparison with previously reported results. A reaction spectrum ranging from full thermal vaporization of the drop, with respective substrate cooling, to complete kinetic disintegration upon impact and surface heating are analyzed. The variation of thermal and kinetic effects across the parametric environment is used to identify those regimes that optimize heat transfer from the surface, as well as those that best facilitate material deposition processes.