Curriculum Vitae - APC - Université Paris Diderot-Paris 7

4.5. Details of the scientific project: What do we want to do?
Again, the primary goal of this project is to understand the collective traffic dynamics of
driven, and motile, particles in fluidic networks. We propose a research program focused on
two main axes corresponding to two classes of experimental systems: 1-Advected droplets
and 2-Self-propelled colloids
4.5.1. Traffic dynamics of droplets driven in microfluidic netwroks.
The first scientific axis of the project is devoted to the case of passive particles advected in
microfluidic obstacle networks. We restrain ourselves to the high current limit (j>j*), see
section 2.2, in which the particles can explore the whole network. Using large droplets, the
advected particles strongly hinder the flow of the continuous phase, and therefore experience
strong hydrodynamics interactions. Note that, using deformable particle greatly facilitates the
experiments, as they allow us to use the same device for several consecutive experiments and
to avoid permanent obstruction of the microchannels.
Generically, the local mobility of the droplets is a nonlinear function of the local capillary
number, Fig. 4. We recall that, the capillary number Ca compares the shear stress to the
Laplace pressure in the droplets and is defined by: Ca=hV/g, where h is the shear viscosity of
the continuous phase, V its local velocity and g is the surface tension. A “critical” capillary
number, Ca*, distinguishes two asymptotic limits: Weak clogging. If Ca>Ca* everywhere in
the network, no obstacle can permanently stop the particles. This typically corresponds to
networks made of channels having a constant width. Strong clogging: oppositely, if locally
Ca