Impacting-bouncing nanodroplets on superhydrophobic surfaces under electric fields

Because electric fields can significantly modify the morphology of impacting droplets, the impact dynamics of droplets subjected to external electric fields have attracted extensive attention in recent years. Owing to the enhanced viscous effect and the altered viscous dissipation mechanisms, nanodroplets show distinctly different impact behaviors from macroscale droplets. However, it is not clear how electric fields affect the impact dynamics of nanodroplets, especially when the field direction is changed. In this study, molecular dynamics (MD) simulations were performed to reveal the bouncing dynamics of a nanodroplet impacting a hydrophobic surface under electric fields with various field strengths and directions. As compared with the case without an electric field, the bouncing dynamics of the nanodroplet were significantly modified in the presence of the electric fields with tilt angles of α = 0°, 30°, 45°, 60°, and 90°, especially when the field strength was higher than 0.08 V Å⁻¹. The restitution coefficient, ε_b, was enhanced by the electric fields at a non-zero α with strengths larger than 0.08 V Å⁻¹. Applying an electric field with α = 60° and ≥ 0.08 V Å⁻¹ would lead to the maximum bouncing velocity. The contact time was stretched by a perpendicular electric field when E ≥ 0.08 V Å⁻¹. When the impact velocity was not sufficient to make a droplet bounce off, an electric field with all directions was capable to cause the opposite.