Effects of Liquid and Surface Properties on Droplet-Film Collision

The transition boundaries of various regimes characterizing the impact outcomes of a droplet upon a liquid layer of small thickness were investigated experimentally. With careful control of the film thickness, the onset of the regimes versus a Weber number, We, specifically when the film size is smaller than the droplet diameter, has been further clarified as compared to prior studies. Several turning, non-monotonic trends between We and the film thickness normalized by droplet diameter, H, were thus identified as H d 1. Furthermore, by adding different percentages of glycerine, the liquid viscosity was varied and thus the effect of another governing parameter, Ohnesorge or Capillary number, could be identified. We have also added surfactant to change the surface tension of the test fluid, which created more variations that would be related to the interaction between the crater and the bottom surface. The material effect of solid surface was also studied for clarification of such interactions. The results show that increasing viscosity would essentially delay the occurrence of these transitions whereas reduced surface tension may encourage the onset.