Molecular dynamics of nanodroplet impact: The effect of particle resolution in the projectile model

The energetic impact of projectiles with diameters between a few nanometers and microns can now be investigated with electrospays operating in the cone-jet mode, a particle source that produces beams of highly charged and monodisperse droplets with average diameters down to a few nanometers. The hypervelocity impact of these nanodroplets on ceramic targets cause sputtering, amorphization and cratering. This experimental phenomenology has been reproduced with molecular dynamics modeling the molecules of the projectile as large pseudo atoms. This model can be over simplistic, especially for liquids made of large molecules, and the goal of this article is to evaluate this uncertainty by comparing the impacts resulting from this coarse model with those of a full atomic model of the molecules. Impact simulations for projectiles of two liquids with dissimilar molecular complexity, formamide and 1-ethyl-3-methylimidazolium bis (trifluoro-methylsulfonyl) imide, show that sufficient resolution of the projectile is needed to reproduce the impact zone, which has a depth of the order of the diameter of the projectile.