Europhys. Lett.
Volume 67, Number 5, September 2004
Page(s) 820 - 826
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 August 2004
Europhys. Lett., 67 (5), pp. 820-826 (2004)
DOI: 10.1209/epl/i2004-10172-y

Dynamics of a rigid rod in a glassy medium

A. 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, $D_{\ab{R}}$, and center-of-mass translational, $D_{\ab{CM}}$, diffusion constants are calculated for a wide range of rod length L and density of obstacles $\rho$. It is found that $D_{\ab{CM}}$ follows the behavior predicted by kinetic theory for a hard disk with an effective radius R(L). A dynamic crossover is observed in $D_{\ab{R}}$ for L comparable to the typical distance between neighboring obstacles $d_{\ab{nn}}$. Using arguments from kinetic theory and reptation, we rationalize the scaling laws, dynamic exponents, and prefactors observed for $D_{\ab{R}}$. In analogy with the enhanced translational diffusion observed in deeply supercooled liquids, the Stokes-Einstein-Debye relation is violated for $L>0.6d_{\ab{nn}}$.

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