Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Abstract
When a drop is deposited gently onto the surface of a layer of the same liquid, it sits momentarily before coalescing into the bottom layer. High-speed video imaging reveals that the coalescence process is not instantaneous, but rather talces place in a cascade where each step generates a smaller drop. This cascade is self-similar and we have observed up to 6 steps. The time associated with each partial coalescence scales with the surface tension time-scale. The cascade will however not proceed ad infinitum due to viscous effects, as the Reynolds number of the process is proportional to square root of drop diameter. Viscous effects will therefore begin to be important for the very smallest drops. This cascade is very similar to the one observed previously by Charles & Mason [J. Colloid Sci. 15, 236 (1960)] for two immiscible liquids, where one of the liquids replaces the air in our setup
