UC San Diego

Droplet impact on liquid film is of critical importance in several industrial applications, such as inkjet printing and thermal sprays. Single-liquid system (same liquid for the droplet and the liquid film) has shown two outcomes for the impact of a droplet on a liquid film, namely bouncing and merging. The transition between the regimes of bouncing and merging has been reported to be a function of the impact Weber number and the film thickness. Very often, in practical application such as in multiple layer 3D printing, the droplet and liquid film are composed of different liquids. Thus, a good understanding of the droplet impact dynamics in two-liquid systems (i.e. different liquid for the droplet and the film) is required to control these processes. However, very few studies in literature have focused on two-liquid systems. In this thesis, we experimentally investigate the dynamics of droplet impact in a two-liquid system with contrasting liquid property ratios. Experimental observations from the two-liquid systems show a significant shift in the transitional boundaries, where droplet impact outcomes change from bouncing to merging, with respect to that of the single-liquid system. In addition to the two types of merging of the droplet to the liquid film, early merging and late merging, reported for single-liquid systems, we also observe a new type of merging for two-liquid systems. Additionally, the findings from experiments have also been reproduced using theoretical analysis.