We present simulations of the motion of a single rigid rod in a disordered static 2d array of disk-like obstacles. The rotational, DR, and center-of-mass translational, DCM, diffusion constants are calculated for a wide range of rod length L and density of obstacles ρ. It is found that DCM follows the behavior predicted by kinetic theory for a hard disk with an effective radius R(L). A dynamic crossover is observed in DR for L comparable to the typical distance between neighboring obstacles dnn. Using arguments from kinetic theory and reptation, we rationalize the scaling laws, dynamic exponents, and prefactors observed for DR. In analogy with the enhanced translational diffusion observed in deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for L > 0.6dnn.
EPL (Europhysics Letters)
- Pub Date:
- September 2004
- Condensed Matter - Disordered Systems and Neural Networks
- 8 pages, 4 figures. Major changes. To be published in Europhysics Letters