Séminaire de Mécanique d'Orsay

Le Jeudi 9 novembre 2023 à 14h00 - Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)

Generation, dynamics and transfer of simple or double emulsions in capillaries


We present a non-embedded co-flow-focusing device, called Raydrop, for single and double-emulsification in microfluidics. Experimental results demonstrate the universality of the device in terms of the variety of fluids that can be emulsified, as well as the range of droplet radii that can be obtained, without neither the need of surfactant nor coating. In a first part, a quasi-static model is developed and shows excellent predictive capability for the size of the droplets. Our results also demonstrate that the mechanism for the dripping-to-jetting transition in this quasi-static limit is intrinsically nonlinear and differs from the absolute-to-convective transition of the Rayleigh-Plateau instability for a jet. In a second part, we focus on the dynamics of droplets and bubbles in microchannels, and specifically on their equilibrium position and velocity, while assessing the influence of their deformability. We then present stability maps for the centred position showing that non-deformable objects dominated by inertial effects are only stable if large enough, typically larger than 0.7 times the channel diameter, whereas deformable objects dominated by capillary effects can be stable for much smaller sizes, except for intermediate viscosity ratios for which deformability also plays a destabilizing role, as for inertia. In a third part, we investigate mass transfer around bubbles and drops flowing in a cylindrical microchannel. We show different concentration patterns and the dependence of the Sherwood numbers for five different regimes in terms of the Péclet number. We finally show some practical examples of micro-encapsulation with double emulsions.

Accès Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)