Defect diffusion and a two-fluid model for structural relaxation near the glass-liquid transition
- Biological Sciences Lab., Schenectady, NY (United States)
- Office of Naval Research, Arlington, VA (United States)
A model is presented for supercooled liquids above the liquid-glass transition containing long-lived order parameter fluctuations, though no average order. The order parameter fluctuations (OPF) are those which would have led to crystallization if their size and concentration had not been kinetically arrested. Being more dense than the isotropic fluid, the regions containing fluctuations are more rigid and relax more slowly. Concentrations of OPF are spatially varying and cause excess light scattering and depolarization, both of which are seen experimentally in polymeric and nonpolymeric glasses. A free energy mismatch between the isotropic fluid and the OPF causes the mixture to attempt to separate into OPF-rich and isotropic-rich fluid phases. As temperature falls mobility is lost; mobile defects in the isotropic fluid control the structural relaxation. This defect diffusion mechanism leads directly to Kohlrausch-Williams/Watts decay, and the phase separation process results in a generalized Vogel-Flucher or WLF temperature dependence as defects cluster and lose mobility. Predictions for the Landau-Placzek ratio and the Vogel behavior agree well with experimental for o-terphenyl. Scaling relations, analogous to those found from mode coupling theories, exist between the {alpha} and {beta} processes, though with different exponents. 26 refs., 3 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 411971
- Journal Information:
- Journal of Physical Chemistry, Vol. 96, Issue 10; Other Information: PBD: 14 May 1992
- Country of Publication:
- United States
- Language:
- English
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