Water nanodroplet impacts on surfaces: Effect of the substrate nature

The impact of 1-5 km/s (H₂O)_n nanodroplets on flat surfaces, with normal or oblique incidence (60°), is modeled using molecular dynamics simulations. The focus is placed on the effect of the substrate, one of the targets being a rigid atomic layer with a repulsive interaction to the droplet, while the other one is a polar surface modeled by three layers of NaCl. In our simulations at 60° incidence, the velocity limit for droplet fragmentation is between 1.5 and 3 km/s for both substrates. However, the dynamics and the energetics of the interaction are very dependent on the substrate nature. While ≤2 km/s droplets glide on the repulsive substrate, keeping most of their translational energy, they stick and stop on the polar substrate, transforming their energy into heat. The influence of the substrate is also pronounced for velocities above the fragmentation threshold, with much higher internal energies and more extensive fragmentation observed for the polar substrate. The results are mainly discussed on the basis of the particle distributions and energy partitions obtained upon interaction. In conclusion, our simulations demonstrate that the nature of the substrate cannot be overlooked in such impact processes.