Dynamics of a rigid rod in a glassy mediumA. J. Moreno1, 2 and W. Kob1
1 Laboratoire des Verres, Université de Montpellier II Place E. Bataillon, CC 069, F-34095 Montpellier, France
2 Dipartimento di Fisica and INFM Udr and Center for Statistical Mechanics and Complexity, Università di Roma "La Sapienza" Piazzale Aldo Moro 2, I-00185 Roma, Italy
(Received 5 April 2004; accepted in final form 21 June 2004)
We present simulations of the motion of a single rigid rod in a disordered static 2d array of disk-like obstacles. The rotational, , and center-of-mass translational, , diffusion constants are calculated for a wide range of rod length L and density of obstacles . It is found that follows the behavior predicted by kinetic theory for a hard disk with an effective radius R(L). A dynamic crossover is observed in for L comparable to the typical distance between neighboring obstacles . Using arguments from kinetic theory and reptation, we rationalize the scaling laws, dynamic exponents, and prefactors observed for . In analogy with the enhanced translational diffusion observed in deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for .
66.30.-h - Diffusion in solids.
05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.
64.70.Pf - Glass transitions.
© EDP Sciences 2004