Curriculum Vitae - APC - Université Paris Diderot-Paris 7

4.1. General context of the project: Why is it interesting?
Hundreds of natural and industrial processes ultimately rely on the transport of mobile agents in
obstacle, or channel, networks. Prominent examples concern: particle filtration, enhance oil
recovery, blood flows in microvessels, Fig. 1A, droplet-based-microfluidics, Fig. 1B, and the
transport of charged (bio)polymers in electrophoresis gels. In all these examples, passive particles
are advected by external force fields and traffic through heterogeneous environment. A second
important class of traffic phenomena deals with self-propelled agents. The most obvious
realizations are the traffic flows of vehicle, and pedestrian in the urban networks, Fig. 1D.
However, numerous similar processes take place in living systems at much smaller scales. Two
representative examples are: (i) the motion of bacteria in polluted soils and in host, or
contaminated, organs [1,2], and (ii) the so-called cytoplasmic streaming, which ensures the
transport of organelles through the eukaryotic cells along the cytoskeletal network, see Fig. 1C.
Figure 1: A- Crossed polarization picture of a microvascular network. Diameter of the smaller vessels: 10
microns, [2] and internet encyclopedia of science. B- Droplet-microfluidic chip. Fission of droplets at Tjunctions,
smallest channel width ~100 microns, from [3]. C- (a) Portion of a plant, with leaf cells (1), nodes (2),
and internodal cells (3). (b) Enlargement of an internodal cell along which helicoïdal cytoplasmic streaming is
observed [4]. D- Vehicle traffic on a Japanese road.
The diversity of the systems, where traffic flows are involved calls for investigating their
universal properties, thereby making the problem highly appealing from a fundamental
perspective. Precisely, we intend to develop a generic understanding of the traffic dynamics in
fluidic networks. We purpose to develop simultaneously two experimental efforts to study
quantitatively these collective phenomena:
- Firstly, we will pursue our work, dedicated to the statistics of advected particles trafficking in
ordered and disordered media. A special attention will be paid to the transition from flowing to
congested states in model microfluidic networks.
- Secondly, we will take advantage of a unique artificial colloidal system to investigate the
collective behaviour of self-propelled particles. We stress that we will address for the first
time the question of the emergence and of the robustness of collective motion in random
networks.
4.2. Position of the project: Whys is it challenging?
Traffic flows in fluidic networks: advected passive particles
The simplest setup we can think about is the transport of small particles passively advected by a
Newtonian fluid through a channel network. In this limit, where there is not interplay between the
motion of the particles and the fluid flow, the transport problem is conceptually very simple. It is
in fact, formally equivalent to the determination of the electric current going through a network of
electric resistors. Whatever, the network geometry, it reduces to the resolution of a set of linear
equations. Conversely, the problem becomes much more challenging when the particle size