Coalescence of a single droplet at a liquid–liquid interface

The coalescence of single drops at a plane liquid–liquid interface has been studied both theoretically and experimentally. Experiments were carried out with a wide range of drop size using two and three component systems. The drops coalesced in a partial manner and the drop size ratios between stages were determined. A detailed examination is made of the rest-time distributions for each stage of coalescence. Generally coalescence rest-times increased with increase in size of drop and fall height of the primary drop. Reasonable agreement between theory and experiment is approached for small drops. Coalescence rest-times of large drops were considerably less than predicted, presumably because of the deformation of the "trapped" film and uneven drainage. The variables affecting the coalescence are analysed and an empirical correlation is formulated to permit prediction of coalescence rest-times. Observations of the motion or the droplet fluid and the disturbed interface were carried out using Schlieren photography. The way in which wave disturbances at the interface can influence the coalescence process is examined. It is shown that that such wave disturbances may be responsible for the existence of the residence time distribution observed in all single drop coalescence studies.