E. Coli suspensions in a confined environment..

GASTÓN L. MIÑO

Zaragoza

Congreso; Granular and Active Fluids. ZCAM Campus Actur; 2011

Due to the presence of autonomous swimmers suspended in a fluid, transport properties of "active fluid" are essentially different from the case of classical suspensions of passive particles. In this presentation, we address two problems of hydrodynamic transport of wild-type E-coli suspensions confined in a micro-fluidic device. We consider the dilute suspension regime and we focus particularly on the influence of solid boundaries.First, a zero flux system is studied in order to explore the effect of complex swimming activity on the Brownian motion problem. Passive tracers are suspended in the active fluid. Their trajectories are tracked and diffusivity is computed. Bacterial motion close to a surface is characterized and two type of motion can be distinguished: ballistic motion (active swimmers) and those showing more a random-like behavior. We found that, with respect to thermal Brownian motion, the tracer diffusivity is enhanced by the presence of active swimmers and increases linearly with the activity of the fluid which is defined as the product of the fraction of active swimmers by their mean velocity. Second, an E. coli suspension is injected into a micro-fluidic channel with a funnel-like constriction. We show an effect of flow induced symmetry breaking in the bacteria distribution along the flow axis. The effect is long range and increases with the flow velocity. We relate this anomalous dispersion effect to elementary mechanisms of interaction between the bacteria and the solid boundaries.