Retraction dynamics of droplets impacting face masks with different roughness

Abstract

Phenomena of droplet impact on solid surfaces are ubiquitous in nature and have been widely explored for industrial applications, such as inkjet printing, anti-icing and spray cooling. Recently, droplet impact on a face mask has been also considered since COVID-19 pandemic. In particular, there have been various studies for evaluating the blockage of the droplets in face masks. However, there are less work for investigating the interaction between the droplet and mask surfaces. Therefore, this work provide the new view on the assessment of face masks based on understanding of the droplet impact dynamics. In this study, we experimentally studied retraction dynamics of droplets after impacting mask surfaces with different roughness and provide a prediction model based on energy analysis. The results indicates that the droplet impacting each surface shows different behaviors affected by retraction dynamics. In addition, we found the droplet impacting the rougher surface showed lower break-up threshold and the retraction dynamics highly affect the break-up phenomena as well. These findings can help understand the retraction dynamics fundamentally and provide an ideal mask surface for preventing the spread of respiratory diseases.