Drop impact upon micro- and nanostructured superhydrophobic surfaces

TL;DR

This study experimentally examines how different superhydrophobic surfaces influence drop impact dynamics, revealing that nanoscale roughness significantly affects splashing behavior at high impact velocities.

Contribution

It provides new insights into the role of multiscale surface roughness on drop impact phenomena across various Weber numbers.

Findings

Impact behavior is similar on different surfaces at low Weber numbers.

Nanoscale roughness influences splashing at high Weber numbers.

Ambient air pressure has negligible effect within studied parameters.

Abstract

We experimentally investigate drop impact dynamics onto different superhydrophobic surfaces, consisting of regular polymeric micropatterns and rough carbon nanofibers, with similar static contact angles. The main control parameters are the Weber number \We and the roughness of the surface. At small \We, i.e. small impact velocity, the impact evolutions are similar for both types of substrates, exhibiting Fakir state, complete bouncing, partial rebouncing, trapping of an air bubble, jetting, and sticky vibrating water balls. At large \We, splashing impacts emerge forming several satellite droplets, which are more pronounced for the multiscale rough carbon nanofiber jungles. The results imply that the multiscale surface roughness at nanoscale plays a minor role in the impact events for small \We $\apprle 120$ but an important one for large \We $\apprge 120$. Finally, we find the effect of ambient air pressure to be negligible in the explored parameter regime \We $\apprle 150$