Mechanism of critical Weber number for superhydrophobic surface roughness regulating droplet splash

Abstract

The texture of superhydrophobic surfaces can reduce solid–liquid contact time by altering the droplet impact dynamics, which is widely used in applications such as self-cleaning and anti-icing. However, the influence of the roughness of superhydrophobic surfaces on the behavior of droplet impact has not been fully elucidated, which limits the engineering applications of such surfaces. In this study, superhydrophobic surfaces with different roughnesses were prepared, and the kinetic behavior of droplets impacting these surfaces for different Weber numbers (We) was systematically analyzed by combining high-speed photographic experiments and hydrodynamic simulations. The results show that the droplets become more thermodynamically unstable due to the significant tensile deformation developed at the droplet retraction stage with increasing We, and secondary droplet splashing occurs due to the Plateau–Rayleigh instability. Moreover, the critical We for a droplet transitioning from complete rebound to breakage splashing decreases monotonically with increasing surface roughness. The physical mechanism of the droplet splashing phenomenon on superhydrophobic surfaces facilitated by surface roughness is elucidated by modeling the quantitative relationship between the air spillage velocity and the initial impact velocity of the droplets, combined with the synergistic analyses of the contact force distributions, the internal velocity field, and the pressure field distributions during the retraction phase of the droplets. This study not only deepens our understanding of the complex physical processes underlying the impact of droplets on superhydrophobic surfaces but also provides a theoretical basis for self-cleaning and anti-icing applications.