8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P10.34Tue 611:23-14:00Colloids in a bacterial bath: simulations and experimentsChantal Valeriani, 1 Martin Li, 1 John Novosel, 1 Jochen Arlt, 1 and DavideMarenduzzo 21 Universidad Complutense Madrid, Departamento de Química Física I, Facultad deCiencias Químicas, Av. Complutense, s/n 28040, Madrid, Spain2 University of Edinburgh, Edinburgh, United KingdomWe present a joint experimental and computational study of the effect of bacterial motion onmicron-scale colloids contained in a two-dimensional suspension of Bacillus Subtilis. With respectto previous work using E. coli, here we introduce a novel experimental set-up that allows usto realise a two-dimensional bacterial suspension insensitive to either evaporation or fluid flow. Byanalysing the mean square displacements of both bacteria and colloids, we confirm the existenceof a crossover from super-diffusive behaviour at short time scales to normal diffusion at longertimes. We also study the same two-dimensional system by means of numerical simulations, usinga suspension of self-propelled dumbbells or the Vicsek model, which has been previously used tostudy the dynamics of active particles. Our numerical results obtained with both models are inbroad agreement with the experimental trends, but only the dumbbell simulations can match theexperimental data quantitatively. The level of agreement we find suggest that steric interactionsdue to collisions are important players in determining collective motion of the bacterial bath, andshould complement hydrodynamic interactions in experiments.34