Formation of droplets and bubbles in a microfluidic T-junction-scaling and mechanism of break-up.

TL;DR: The formation of droplets and bubbles in microfluidic T-junctions is dominated by pressure drop across the emerging droplet or bubble. A simple scaling relation accurately predicts the size of droplets and bubbles produced in T-junctions.

Abstract: This article describes the process of formation of droplets and bubbles in microfluidic T-junction geometries. At low capillary numbers break-up is not dominated by shear stresses: experimental results support the assertion that the dominant contribution to the dynamics of break-up arises from the pressure drop across the emerging droplet or bubble. This pressure drop results from the high resistance to flow of the continuous (carrier) fluid in the thin films that separate the droplet from the walls of the microchannel when the droplet fills almost the entire cross-section of the channel. A simple scaling relation, based on this assertion, predicts the size of droplets and bubbles produced in the T-junctions over a range of rates of flow of the two immiscible phases, the viscosity of the continuous phase, the interfacial tension, and the geometrical dimensions of the device.