Prince Rupert's Drop bouncing on high-speed moving superhydrophobic surfaces

Abstract

Superhydrophobic surfaces have shown huge potential in diverse fields. However, the hydrodynamics of droplet impacting on moving superhydrophobic surfaces are largely unexplored, especially for surfaces with a high moving velocity. The knowledge gap in liquid-solid interaction between impacting droplets and high-speed moving superhydrophobic surfaces should be filled to better guide practical engineering applications. Here, a superhydrophobic surface is fabricated as the experimental surface by a chemical deposition-etching method and droplet impacting experiments on horizontally moving superhydrophobic surfaces (realized by impacting the edge of a rotating surface) are systematically conducted. The moving velocity of superhydrophobic surfaces reaches nearly 10.0 m/s, which is approximately three times the velocity in previous relevant studies. The results show that the droplet spreading is greatly enhanced when the surface velocity exceeds a critical value, and it is independent of the droplet Weber number (We). The droplet detaches from the surface in the shape of “Prince Rupert's Drop”, reducing the contact time by over 40%. The critical surface velocity is characterized by We/We_s = 0.17, where We_s is the Weber number of the moving surface. To reveal the dynamics of Prince Rupert's Drop bouncing, scaling laws of the maximum spreading coefficient and the contact time are developed, which agree well with experimental results.