Abstract

In this talk, I will highlight two aspects of droplet-based microfluidics. First, I will discuss if droplet formation in co-axial injectors can be understood in terms of the spatio-temporal propagation of instabilities, concepts rarely used in the context of creeping flows. I will present our recent experimental analysis of the dripping and jetting regimes and compare them to the theoretical predictions issuing from the instability theory in terms of frequency and wavenumber selection. We also explore the behavior of the jetting regime as a noise amplifier by means of a pulsating laser beam to locally force the flow. While no reaction is observed in the dripping regime, a strong synchronization occurs in the jetting regime.

Second, I will discuss how droplets flowing in microchannels can be guided and trapped by creating external surface energy gradients, either by using a focussed laser beam or by introducing depth variations. I will present counterintuitive experiments, conducted in presence of surfactants, where thermocapillary and solutocapillary effects enter in competition.

This work is done in collaboration with M.-L. Cordero, R. Dangla and C. Baroud.