Hydrodynamic field around a Brownian particle.

We use molecular dynamics simulations of a solid Brownian particle in an explicit solvent to analyze the velocity field generated by a stochastic motion of a particle. The simulation data demonstrate that the amplitude of the velocity field around a Brownian particle decays much faster than the velocity field around a particle moving with a constant velocity. However, the time-integrated response of the velocity field around a Brownian particle has exactly the same distance dependence as the velocity field around a particle moving with a constant velocity. This finding elucidates the validity of an assumption used in theoretical descriptions of Brownian particles dynamics in confined geometries and in colloids; namely, that viscous drag forces can be computed as if the particles move with constant velocities.