Droplet impact onto a solid sphere: Effect of wettability and impact velocity

Collision of a droplet onto a still spherical particle was experimentally investigated. The effect of droplet impact velocity and wettability of the particle surface on collision outcomes was studied (0.05 < V-0 < 5.0 and theta = 70 degrees, 90 degrees, 118 degrees). Compared to the literature, the range of Weber number variations was significantly extended (0.1 < We < 1146), and while focus of the previous works was on impacts in which particle is larger than the droplet (Dr < 1), the drop to particle diameter ratio in this work was larger than one. Therefore, formation of a thin liquid film, i.e., lamella, was observed due to impact of a relatively high velocity droplet onto a hydrophobic particle. Temporal variations of various geometrical parameters of collision outcomes including lamella length and lamella base diameter were investigated during the impact. It was also shown that for hydrophobic targets, the extent of hydrophobicity of the particle does not affect the lamella geometry. A comprehensive map of all the available works in drop impact on a spherical target was also provided. Published by AIP Publishing.