Hauptseminar Soft Matter SS 2019/Active Brownian particles

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Active Brownian particles
Smruti Manjunath
Mihail Popescu


Active particles, a term that include self-propelled chemically active colloids, microswimmers and nanoswimmers, are capable of taking up energy from their environment and converting it into directed motion. This intrinsically involves out of equilibrium processes and the current understanding of the phenomenology remains rather limited. Accordingly, a significant part of the theoretical modelling follows a trial-and-error method, in with simple models are developed by extending well established equilibrium Statistical Physics concepts via a heuristic addition of "self-propulsion" terms.

One of such models is the so-called "Active Brownian Particle" (ABP), which builds upon the classical Brownian motion of a colloid by adding to it a steady rigid body translation along a body-fixed direction as well as a steady rigid body rotation [1-3]. For spherical and ellipsoidal shapes with just translational self-propulsion, the overdamped dynamics of a single particle is sufficiently simple that detailed information on the moments of various order of the displacement, and in particular the mean squared root displacement, can be obtained analytically [1]. The derivation of these single particle results, as well as certain heuristic extensions of this model to studies of collective effects ("active dry matter") [3], will be critically reviewed.


  1. B. ten Hagen et al, J. Phys.: Condens. Matter 23, 194119 (2011)
  2. C. Lozano et al, Nat. Commun. 7, 12828 (2016)
  3. M. E. Cates and J. Tailleur EPL 101 20010 (2013)