Liquid Droplet Impact Dynamics on Micro-Patterned Superhydrophobic Surfaces

This fluid dynamics video (Liquid Droplet Impact Dynamics on Micro-Patterned Superhydrophobic Surfaces) exhibits experimental qualitative and quantitative results of water/glycerol (50%/50 % by mass) droplet impact on two types of micro-patterned superhydrophobic surfaces. The two types of surfaces used were 80 % cavity fraction (structured such that the liquid is in contact with 20 % of the surface) ribs and posts with a periodic spacing of 40 microns and 32 microns, respectively. All surfaces were manufac-tured through photolithography. The impact Weber number is defined as We = ρV 2D/σ, where ρ is the average density of the water/glycerol mix-ture, V is the impact velocity, D is the droplet diameter before impact, and σ is the surface tension. Weber number is used as the dynamic parameter to compare droplet splashing after impact and subsequent rebound behaviors between the two types of surfaces. While droplets exhibit similar dynamics on both rib and post structured surfaces at low Weber numbers, rebound jet speed (normalized by droplet impact speed) is notably higher on posts than ribs for all Weber numbers tested here (5 < We < 900). At elevated Weber numbers, droplets splash peripherally. These side droplets created at splash are referred to as satellite droplets. Top view videos show the significant difference in splashing behavior for the two surface types. On ribs, satellite droplet formation consistently prefers a path 60 ◦ from the ribs longitudi-nal direction. This behavior prevails for Weber numbers greater than 150, however, distinguished splashing does not occur for We> 265. On posts, 1 a