Prof Thomas Speck

Collective behavior of Active Brownian particles

In the first part, I will report on recent experiments implementing arbitrary interaction rules between self-propelled colloidal particles. Specifically, we study aggregation at low density through quorum sensing, that is, the change of motility (i.e., the propulsion speed) due to the sensed concentration of signaling molecules released by all members of a population. The observed behavior is in excellent agreement with simulations and a mean-field theory of active Brownian particles, a minimal model system of active particles. In the second part, I return to the situation of constant propulsion speed without quorum sensing. In this case we observe non-equilibrium phase coexistence between a dilute gas and a dense phase. I will discuss the current state of a possible thermodynamic description.