Designing Assembly of Meshes Having Diverse Wettability for Reducing Liquid Ejection at Terminal Velocity Droplet Impact

In this paper, we have studied the effect of surface wettability and geometrical parameters on the velocity of the ejecting jet during droplet impacts on meshes. This paper presents detailed experiments and modeling which helps in explaining a previous demonstration, where an assembly of meshes with different wettabilities was used to significantly reduce the amount of liquid leakage during impact of droplets travelling at terminal velocity. Drop impact on meshes at various Weber numbers (We) was captured using high-speed imaging. At higher We, the velocity of the ejected liquid jet (Vi) was found to be higher than the velocity of the impacting droplet (Vd) for most of the superhydrophobic meshes. In contrary, for all values of We the velocity of the ejected liquid through superhydrophilic meshes was lower than the droplet velocity for all meshes. While jet width for superhydrophobic mesh was close to the pore opening dimension, in case of superhydrophilic mesh merging of the ejected jets meant that the width was close to the impacting droplet diameter. A combination of superhydrophilic and superhydrophobic mesh was used to significantly reduce liquid ejection for droplet impact at terminal velocity (~8 m/s). Less than 6 × 10
^-5
% volume ejection was observed for the designed combination. This configuration can be used to fabricate rain repellent air-transparent surfaces.