The effects of surface wettability on droplet fingering

In this paper high speed visualisation has been used to investigate the effects of surface wettability on the droplet impingement and fingering behaviour. Three surfaces have been studied: a reference surface with contact angle θ = 90º, a hydrophilic surface with θ = 15º and a hydrophobic surface with θ = 165º. Droplet Weber numbers (We) ranging from 50 to 250 were studied. The reference surface showed no fingering across the range of Weber numbers tested. Fingering was found to occur on the hydrophilic surface for We > 150, whereas the hydrophobic surface exhibited fingering for We > 100. Above these thresholds the observed number of fingers around a droplet was found to be consistent between the surfaces.