Spreading patterns of high velocity nanodroplets impacting on suspended graphene

Abstract

The determination of the wettability of 2D materials is an area of intensive research, as it is decisive on the applications of these systems in nanofluidics. One important part of the wetting characterization is how the spreading of droplets impacting on the surfaces occurs. However, few works address this problem for layered materials. Here, we report a fully atomistic molecular dynamics study on the dynamics of impact of water nanodroplets (100 Å of diameter) at high velocities (from 1 up to 15 Å/ps) against graphene targets. Our results show that tuning graphene wettability (through parameter changes) significantly affects the structural and dynamical aspects of the nanodroplets. We identified three ranges of velocities with distinct characteristics, from simple deposition of the droplet to spreading with rebound, and finally droplet fragmentation. We also identify that in an intermediary velocity of 7 Å/ps, the pattern of spreading critically changes, due to formation of voids on droplet structure. These voids affect in a detrimental way the droplet spreading on the less hydrophilic surface, as it takes more time to the droplet recover from the spreading and to return to a semi-spherical configuration. When the velocity is increased to values larger than 11 Å/ps, the droplet fragments, which reveals the maximum possible spreading.