  When particles suspended in a fluid are driven through a regular lattice of
cylindrical obstacles, the particle motion is usually not simply in the
direction of the force, and in the high Peclet number limit particle
trajectories tend to lock along certain lattice directions. By means of
molecular dynamics simulations we show that this effect persists in the
presence of molecular diffusion for nanoparticle flows, provided the Peclet
number is not too small. We examine the effects of varying particle and
obstacle size, the method of forcing, solid roughness, and particle
concentration. While we observe trajectory locking in all cases, the degree of
locking varies with particle size and these flows may have application as a
separation technique.
