Partial Coalescence of Aqueous Droplets on Liquids-Liquid Interfaces

Abstract: When droplets approach a liquid-liquid interface they may not always completely merge with their homophase, but they may leave secondary droplets resulting in partial coalescence. The phenomenon can repeat itself several times producing different sizes of daughter droplets and extending the coalesce time, which affects processes like the separation of two liquids in coalescers. Despite the number of studies on partial coalescence the mechanism is still not clear. In this work, a 2-dimensional high-speed PIV study is carried out on the coalescence of millimetric aqueous droplets at the interface of liquid/liquid systems. By analysing the velocity fields as well as the morphology of the coalescing droplet, the reason for the partial coalescence is explained phenomenologically. Furthere, simulations are conducted on the same systems as the experiments using the VOF model. The initial shape of the deformed droplet and the phase interface from the experiments are used to initialize the simulation. The advantages and shortcomings of applying 2D PIV in the study of 3-dimensional coalescence are discussed by comparing the experimental results to the simulations.