Dynamical behavior of droplets transiently impacting on superhydrophobic microstructures

Abstract

Superhydrophobic microstructures (100 μm–1 mm) on a solid surface can change the droplet impact dynamics and reduce the contact time, both of which are potentially relevant for various industrial applications. In the study described here, the effects of two superhydrophobic microstructures are compared: a uniformly distributed convex hull structure and a striated structure. Droplet impact dynamics are simulated for a wide range of impact velocities (0.15 m/s–4.4 m/s) with the aim of quantitatively recording the morphological changes in droplets and the formation of splashed droplets using the curves of the spreading diameter and contact diameter vs time. Different types of bouncing behavior are also investigated. The results indicate that an increase in the impact velocity leads to a transition from rebound with full retraction, to a rebound without full retraction, then to a rebound with splashed droplets, and finally to a splashing phenomenon. The special morphologies during rebounding are also analyzed, in particular, pancake bouncing and bouncing in the flying-eagle configuration. The former had no significant change in contact time, owing to reattachment occurring, but the latter can reduce the contact time by 27.6% for an impact velocity of 1.4m/s. Finally, the dynamic behavior is quantitatively characterized, with a focus on the analysis of the maximum spread diameter, maximum retraction velocity, and contact time. As the impact velocity increases, the first two increase, but the third decreases. A sharp drop in the contact time at a high impact velocity is found to be due to the occurrence of the splashing phenomenon.