Droplet Splashing on Rough Surfaces

TL;DR

This study investigates how surface roughness influences droplet splashing velocity, revealing that increased roughness shifts the mechanism from corona to prompt splashing and that splashing velocity scales with the Ohnesorge number.

Contribution

It demonstrates that surface roughness affects droplet splashing mechanisms and introduces a scaling model linking splashing velocity to the Ohnesorge number based on roughness.

Findings

Splashing velocity depends on surface roughness when it disrupts lamella spreading.

Transition from corona to prompt splashing occurs at higher roughness levels.

Splashing velocities for different liquids collapse onto a single curve when scaled with the Ohnesorge number.

Abstract

When a droplet hits a surface fast enough, droplet splashing can occur: smaller secondary droplets detach from the main droplet during impact. While droplet splashing on smooth surfaces is by now well understood, the surface roughness also affects at which impact velocity a droplet splashes. In this study, the influence of the surface roughness on droplet splashing is investigated. By changing the root mean square roughness of the impacted surface, we show that the droplet splashing velocity is only affected when the droplet roughness is large enough to disrupt the spreading droplet lamella and change the droplet splashing mechanism from corona to prompt splashing. Finally, using Weber and Ohnesorge number scaling models, we also show that the measured splashing velocity for both water and ethanol on surfaces with different roughness and water-ethanol mixtures collapse onto a single curve, showing that the droplet splashing velocity on rough surfaces scales with the Ohnesorge number defined with the surface roughness length scale.