Enhanced diffusion of a needle in a planar array of point obstacles

The transport of an infinitely thin, hard rod in a random, dense
array of point obstacles is investigated by molecular dynamics
simulations. Our model mimics the sterically hindered dynamics in
dense needle liquids. Transport becomes increasingly fast at higher
densities, and we observe a power-law divergence of the diffusion
coefficient with exponent 0.8. This phenomenon is connected with a
new divergent time scale, reflected in a zigzag motion of the
needle, a two-step decay of the velocity-autocorrelation function,
and a negative plateau in the non-Gaussian parameter. Finally, we
provide a heuristic scaling argument for the new exponent.