(349a) Bubble-Bubble Dynamics Examined Using Microfluidic Channels

Recent experimental work has demonstrated that close confinement of bubbles can facilitate neighbor-neighbor bubble pinch-off, where the strong interactions of two or more bubbles break a central elongated bubble. This “structure-induced capillary instability” elucidated the process of bubble breakup in sheared foams and manifested in the discovery of two fundamental pore-level mechanisms of foam generation in porous media. The present work offers a novel microfluidic foam generation system for production of ordered, bi- or tridisperse foams at capacities exceeding 10,000 daughter bubbles per second.Bubble-bubble pinch-off occurs near the entrance of the expansion region of a wide 1600 µm collection channel. Pinch-off is systematic at sufficiently large strain rates, assisted by a clear templating effect from the bubbles in the expansion.The relationship between the capillary number, the upstream shear rate, and the size distribution of fragmented bubbles is examined. The banded size segregation of fragmented and intact bubbles is primarily governed by the channel geometry, and the foams remain ordered as they flow through the collection channel.The mechanism of bubble-bubble pinch-off in an expansion differs from the corresponding neighbor-neighbor pinch-off phenomenon discovered in pore constriction studies. The use of bubble-bubble pinch-off for tridisperse foam generation allows for the fluidic resistance to be adjusted to access a spectrum of bubble size ratios for a fixed expansion wall geometry. The simplicity in operating and characterizing our system will broaden microfluidic foam research by enabling studies on dynamic bubble interactions and higher complexity foam flows.