In this presentation, we will deal with the mechanism of droplets formation and with droplets traffic in microfluidic network.
First, we will study both theoretically and experimentally the stability of jets formed
by pressure-driven concentric biphasic flows in various microfluidic geometries . We experimentally evidence a transition between situations where theflow takes the form of a jet and regimes where drops are produced. Its description as the transition from a convective to an absolute instability, within a simple linear analysis using lubrication theory for low Reynolds flows, yields remarkable agreement with the data. This description captures the role of the various parameters such as viscosity ratio, flow rates ratio, shape geometries.
Second, we will deal with droplets traffic in microfluidic network .
We report that, when a train of confined droplets flowing through a channel reaches a junction, the droplets either are alternately distributed between the different outlets or all collect into the shortest one. We argue that this behavior is due to the hydrodynamic feedback of droplets in the different outlets on the selection process occurring at the junction. A "mean field" model, yielding semiquantitative results, offers a first guide to predict droplet traffic in branched networks. To conclude, we will present some new experiments allowing us to measure the hydrodynamic resistance of droplets.