Nanodroplet impacts on hydrophobic/superhydrophobic surfaces with point textures

Abstract

Reducing the contact time between droplets and solid surfaces is important in anti-icing surface design. The present work investigates the impact dynamics of nanodroplets on hydrophobic/superhydrophobic surfaces decorated by point textures via molecular dynamics (MD) simulations, aiming to significantly reduce the contact by the point textures. Based on distinguishing outcome regimes into a phase diagram, the point texture is found to not affect the outcome regimes of sticky, bouncing, and splash, whereas the internal rupture regime is significantly enhanced so that the new outcome in this regime, ring-bouncing, which is reported for the first time at the nanoscale, is also significantly reinforced. Impacting nanodroplets with ring-bouncing behaviors have remarkably reduced the contact time due to the saved retraction time via creating a retraction of both inner and outer contact lines. Subsequently, an energy conservation equation from the initial to the bouncing states is established for identifying the boundary of this outcome regime, which shows good agreement with the outcome phase diagram. Finally, impacting nanodroplets with three diameters of 8, 10, and 14 nm are implemented for understanding how the ratio of the droplet size to the texture point affects the reduction of the contact time. The MD results show the cases of 8-nm nanodroplets displaying the best performance of reducing the contact time by 52%, which is superior to current studies in reducing the contact time at the nanoscale. This can be explained by the lower ratio of droplet diameter to texture size leading to a further shorter distance of retraction after the internal rupture and hence a shorter contact time.