Enhanced diffusion due to active swimmers at a solid surface

Gaston Miño (1) , Thomas Mallouk (2) , Thierry Darnige (1) , Mauricio Hoyos (1) , Jeremy Dauchet (1) , Jocelyn Dunstan (3) , Rodrigo Soto (3) , Yang Wang (2) , Annie Rousselet (1) , Eric Clement (1)

1 PMMH - Physique et mécanique des milieux hétérogenes (UMR 7636)
2 Department of Chemistry, The Pennsylvania State University
3 Departamento de Fisica [USACH Santiago]

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type E. coli and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing diffusive-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 and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers.

Mots clés: Diffusion; E. coli; Au-Pt rods; Active swimmers

Domaines: Matière Molle [cond-mat.soft]; Biophysique [physics.bio-ph]

Gaston Miño, Thomas Mallouk, Thierry Darnige, Mauricio Hoyos, Jeremy Dauchet, et al.. Enhanced diffusion due to active swimmers at a solid surface. 2010. ⟨hal-00514947⟩