Anomalous diffusion in heterogeneous glass-forming liquids: temperature-dependent behavior

Area of Science:

• Condensed matter physics
• Materials science
• Statistical mechanics

Background:

• Previous research established non-Gaussian diffusion and heterogeneity-correlation decay in glass-forming liquids near the glass transition.
• The current study investigates these phenomena at higher temperatures where thermal activation barriers decrease and heterogeneities diminish.

Purpose of the Study:

• To extend the analysis of molecular diffusion in heterogeneous glass-forming liquids to higher temperatures.
• To reconcile theoretical models with experimental data for orthoterphenyl, focusing on diffusion, viscosity, and scattering functions.

Main Methods:

• Modification of continuous-time random-walk theory.
• Extension of excitation-chain theory for glass dynamics.
• Incorporation of results from shear-transformation-zone theory.
• Analysis of experimental data including diffusion coefficients, viscosity, and neutron scattering measurements.

Main Results:

• Insights into the crossover from super-Arrhenius to Arrhenius dynamics.
• Characterization of the length scales of spatial heterogeneities.
• Explanation for the violation of the Stokes-Einstein relation in glass-forming liquids.
• Understanding the origin of stretched-exponential decay of correlations.

Conclusions:

• The extended theoretical framework successfully interprets experimental data for orthoterphenyl.
• The study provides a unified view of dynamics, heterogeneity, and transport properties in glass-forming liquids across different temperature regimes.