A model for viscous liquid dynamics

Jeppe C. Dyre,

Roskilde University, Denmark

Mon, Nov. 20th 2006, 14:15

Salle Claude Itzykson, Bât. 774, Orme des Merisiers

Glass-formation is a general property of liquids, an unavoidable process if the
liquid is
cooled fast enough to avoid crystallization. We first give an overview of the physical
properties of highly viscous liquids, emphasizing the universal features. The most
common phenomenological models are then briefly reviewed. The main focus of the talk
is on a description of highly viscous liquids based on a standard time-dependent
Ginzburg-Landau equation for the density dynamics, supplemented by the assumption of
long-wavelength dominance of the dynamics [1]. The density field is described as a non-
conserved field, a feature which reflects the "solidity" of highly viscous liquids -
the
property that they are more like solids that flow, than like ordinary, less-viscous
liquids.
The long-wavelength dominance assumption implies that one may assume an ultralocal
Hamiltonian, thus simplifying the model quite a lot. We finally show how the case with
just a third-order term is able to reproduce the (conjectured) generic property of
viscous
liquids that the high-frequency decay of the alpha (main) relaxation process varies
with
frequency as $\omega^{-1/2}$ [2]. Basically, this comes from a "long-time-tail
mechanism,
working at a range of short times."
Refs:
1. J. C. Dyre, Europhys. Lett. 71, 646 (2005); Phys. Rev. E 74, 021502 (2006).
2. N. B. Olsen et al, Phys. Rev. Lett. 86, 1271 (2001).