Non-equilibrium dynamics of an active colloidal "chucker"

We report Monte Carlo simulations of the dynamics of a "chucker," a colloidal particle that emits smaller solute particles from its surface, isotropically and at a constant rate k(c). We find that the diffusion constant of the chucker increases for small k(c), as recently predicted theoretically. At large k(c), the chucker diffuses more slowly due to crowding effects. We compare our simulation results to those of a "point particle" Langevin dynamics scheme in which the solute concentration field is calculated analytically, and in which hydrodynamic effects arising from colloid-solvent surface interactions can be accounted for in a coarse-grained way. By simulating the dragging of a chucker, we obtain an estimate of its apparent mobility coefficient which violates the fluctuation-dissipation theorem. We also characterize the probability density profile for a chucker which sediments onto a surface which either repels or absorbs the solute particles, and find that the steady state distributions are very different in the two cases. Our simulations are inspired by the biological example of exopolysaccharide-producing bacteria, as well as by recent experimental, simulation and theoretical work on phoretic colloidal "swimmers.". (C) 2010 American Institute of Physics. [doi: 10.1063/1.3428663]