Eur. Phys. J. E 5, 229-243
Glassy dynamics of simulated polymer melts: Coherent scattering and van Hove correlation functions
Part I: Dynamics in the 
-relaxation regime
M. Aichele1 and J. Baschnagel2
1 Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudinger Weg 7, 55099 Mainz, Germany
2 Institut Charles Sadron, 6 rue Boussingault, 67083 Strasbourg Cedex, France
(Received 17 January 2001)
Abstract
We report results of molecular-dynamics simulations of a
model polymer melt consisting of short non-entangled chains in the
supercooled state above the critical temperature
Tc of
mode-coupling theory (MCT). To analyse the dynamics of the system, we
computed the incoherent, the collective chain and the collective melt
intermediate scattering functions as well as their space Fourier
transforms, the van Hove correlation functions. In this first part of
the paper we focus on the dynamics in the -relaxation regime.
The final structural relaxation, the 
-relaxation, will be
studied in the following second part. The results can be summarized
as follows: Without using any fit procedure we find evidence for the
space-time factorization theorem of MCT in real and reciprocal space,
and also for polymer-specific quantities, the Rouse modes. The
critical amplitudes in real space are determined directly from the
simulation data of the van Hove correlation functions. They allow to
identify the typical length scales of the -dynamics, and
illustrate that it is a localized process. In a quantitative analysis
the wave vector dependences of the -coefficients, i.e., of the
non-ergodicity parameter, the critical amplitude, and the
next-to-leading order correction coefficients, are studied for all
correlators. The -coefficients show indications of polymer-specific
effects on the length scale of the chain's radius of
gyration. The agreement between simulation and the leading-order MCT
description is found to be good in the central -regime.
Next-to-leading order corrections extend the validity of the MCT
approximations to a greater time window and become more important at
large wave vectors.
64.70.Pf - Glass transitions.
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
61.20.Ja - Computer simulation of liquid structure.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
