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Our paper entitled “Tuning Bubbly Structures in Microchannels,” by S.M. Vuong and S.L. Anna, was published in Biomicrofluidics, Special Issue on Multiphase Microfluidics, Guest Ed. Saif Khan, 6 (2012) 022004.

Bubble shapes and structures organized in terms of volume fraction and bubble size

Abstract: Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row (“dripping”), to multiple rows (“alternating”), to densely packed bubbles (“bamboo” and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate nitrogen bubbles in surfactant-stabilized water and water droplets in surfactant-stabilized oil. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters.