Dynamics of a rigid rod in a glassy medium

A. J. Moreno; W. Kob

doi:10.1209/epl/i2004-10172-y

All issues

Volume 67 / No 5 (September 2004)

Europhys. Lett., 67 5 (2004) 820-826

Abstract

Issue		Europhys. Lett. Volume 67, Number 5, September 2004


Page(s)		820 - 826
Section		Condensed matter: structure, mechanical and thermal properties
DOI		https://doi.org/10.1209/epl/i2004-10172-y
Published online		01 August 2004

Europhys. Lett., 67 (5), pp. 820-826 (2004)

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: 21 June 2004

Abstract

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 ρ . 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 $L>0.6d_{\ab{nn}}$ .

PACS: 66.30.-h – Diffusion in solids / 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion / 64.70.Pf – Glass transitions

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