Dynamics of a rigid rod in a glassy medium

We present simulations of the motion of a single rigid rod in a disordered static 2d array of disk-like obstacles. The rotational, D-R, and center-of-mass translational, D-CM, diffusion constants are calculated for a wide range of rod length L and density of obstacles p. It is found that D-CM follows the behavior predicted by kinetic theory for a hard disk with an effective radius R(L). A dynamic crossover is observed in D-R for L comparable to the typical distance between neighboring obstacles d(nn). Using arguments from kinetic theory and reptation, we rationalize the scaling laws, dynamic exponents, and prefactors observed for D-R. In analogy with the enhanced translational diffusion observed in deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for L > 0.6d(nn).