(435g) Block-and-Break Generation of Microdroplets with Fixed Volume

Microfluidic devices produce monodisperse drops with a high-level of control over size and contents, making them useful for applications in biotechnology, material synthesis, optofluidics, and medical diagnostics. Drop volume depends on the flow rates, which makes it easy to tune. It, however, also sets strict requirements on the stability of flows for the generation of monodisperse drops, as variations in flow lead to corresponding variations in volume.

In this work, we introduce a novel type of microfluidic droplet generator that produces droplets of a volume set by the geometry of the droplet generator, and not by the rates of flow of the liquids. The generator consists of a classic T-junction with a bypass channel. This bypass directs the continuous fluid around the forming droplets, so that they can fill the space between the inlet of the dispersed phase and the exit of the bypass without breaking. Once filled, the droplets block the exit of the bypass and are squeezed by the continuous fluid, which leads to their pinch-off. We illustrate the potential of this fixed-volume droplet generator for i) forming monodisperse droplets from a source of varying rates of flow, ii) forming monodisperse droplets containing a gradation of solute concentration, and iii) producing monodisperse droplets in parallel.