(381a) Coalescence of an Oil Droplet with Water: Regimes and Scaling Laws

When an oil droplet merges with a pool of liquid it undergoes several transformations simultaneous to its spreading. Literature thus far has examined the dynamics in the late stages of this spreading when the oil drop has transformed into a film. Although the spreading is monotonic at these final times, the early time behavior has not been studied. In this work, we use high speed imaging to experimentally investigate the dynamics of drop deformation and spreading during gentle deposition of an oil drop onto an air-water interface. This results in either partial or complete coalescence of the drop depending on the viscosity of the oil drop and is delineated using a regime map comprising of the relevant non-dimensional parameters. Notably, the salient morphological features are seen to scale with the physical properties of the drop. Similarly, the spreading behavior of the drop during early times of its coalescence is characterized and found to display a non-monotonic behavior which can be modeled using a theoretical model based on the damped harmonic motion. We anticipate our results to have a tremendous bearing on applications such as oil spills, synthesis of emulsions for drug delivery and oil recovery.