Séminaire Institut

Vendredi 18 Février 2011 à 14h00.

''Active suspensions is the name borne by fluids laden with self-swimming entities such as bacteria , algae or collections of active artificial swimmers . Assemblies of such microscopic motors dispersed in a fluid display emergent properties that may differ strongly from passive suspensions. > In this conference, I will present a recent work by Mino et al.( PRL 106, 048102 (2011)) in which we consider two systems of active swimmers moving close to a solid surface. The first is a living population of wild-type E. Coli and the other, an assembly of self-propelled Au-Pt rods. In both cases, we identified two types of motion at the surface and evaluated the fraction of the population displaying ballistic trajectories (active swimmers) with respect to those showing random like > behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers > also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard > Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction > of active swimmers by their mean velocity. > I will discuss the implication of this results both on the possibility to model numerically active systems close to a boundary and also on the possibility of new emergent transport properties when collective motion starts on.''