Dresden 2011 – scientific programme

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BP: Fachverband Biologische Physik

BP 6: Statistical Physics of Biological Systems II (joint DY, BP)

BP 6.4: Talk

Monday, March 14, 2011, 15:00–15:15, HÜL 186

Active colloidal suspensions exhibit orientational order under gravity — •Mihaela Enculescu und Holger Stark — Technische Universität Berlin, Institut für Theoretische Physik, Hardenbergstr. 36, 10623 Berlin

Recently, the steady state of an active colloidal suspension under gravitational field was studied experimentally in [J.Palacci et al, Phys.Rev.Lett. 105, 088304 (2010)]. It was found that the sedimentation length depends strongly on the velocity of the active Brownian particles. We present a theoretical analysis for the sedimentation of an active colloidal suspension. We find that the change of the sedimentation length is coupled to a partial alignment of the suspension with the mean swimming direction oriented against the gravitational field. Our approach starts from Langevin equations of non-interacting active particles, from which a Smoluchowski equation for the particle distribution is derived. We determine the stationary particle distribution both numerically and by perturbation theory. It agrees very well with the experimental data. The predicted anisotropy in the particle orientational distribution is found to depend on the particle activity, as well as on the gravitational force.