Events in Physics

On the “phase behaviour” of active particles

The study of active particles is an emerging field, which describes objects as diverse as self-propelled bacteria or janus-type colloidal particles propelled by catalytic reactions. These systems are intrinsically out of equilibrium.

In our molecular dynamics simulations we use a continuous Asakura-Oosawa [1] model as a reference system, for which the phase diagram is well-known. The AO model consists of two particle types, colloids and polymers, and exhibits phase transition due to depletion forces. The colloids are made active by adding a Vicsek-type activity [2, 3] to the particles: Each colloid is subject to an additional constant force applied in the direction of the mean velocity of neighbouring colloids. We demonstrate that the addition of this force facilitates phase separation [4].

[1] J. Zausch, P. Virnau, K. Binder, J. Horbach and R.L.C. Vink, J. Chem. Phys. 130, 064906 (2009); [2] T. Vicsek, A. Czirók, E. Ben-Jacob, I. Cohen and O. Shochet, Phys. Rev. Lett. 75, 1226 (1995); [3] A. Czirók and T. Vicsek, Physica A 281, 17 (2000); [4] S. K. Das, S. Egorov, B. Trefz, P. Virnau and K. Binder, arXiv:1308.5831 [cond-mat.stat-mech]