Hydrodynamic interactions enhance the performance of Brownian ratchets

Abstract

We investigate how hydrodynamic interactions between Brownian particles influence the performance of a fluctuating ratchet. For this purpose, we perform Brownian dynamics simulations of particles that move in a toroidal trap under the influence of a sawtooth potential which fluctuates between two states (on and off). Hydrodynamic interactions are included in the Rotne-Prager approximation. We first consider spatially constant transition rates between the two ratchet states and observe that hydrodynamic interactions significantly increase the mean velocity of the particles but only when they are allowed to change their ratchet states individually. If in addition the transition rate to the off state is localized at the minimum of the ratchet potential, particles form characteristic transient clusters that travel with remarkably high velocities. The clusters form since drifting particles have the ability to push but also pull neighboring particles due to hydrodynamic interactions.