Medium-Range Order, Density Fluctuations, and Activated Relaxation in the Equilibrated Deep Glass Regime

Area of Science:

• Condensed matter physics
• Materials science
• Statistical mechanics

Background:

• Metastable supercooled liquids exhibit complex dynamics near the glass transition.
• Understanding the behavior of glass-forming materials in the deep glass regime is crucial for materials science.
• Existing theories often struggle to explain dynamics over vast timescales.

Purpose of the Study:

• To extend a microscopic theory of activated relaxation to the equilibrated deep glass regime.
• To investigate the relationship between dynamic barriers and scalar order parameters in glasses.
• To reconcile theoretical predictions with experimental data on aged glass-forming liquids.

Main Methods:

• Extension of a microscopic theory for activated relaxation.
• Analysis of power-law scaling relationships between dynamic barriers and order parameters (correlation length, compressibility, shear modulus).
• Quantitative comparison with experimental data for aged glass-forming liquids over extended timescales.

Main Results:

• The predicted power-law scaling of dynamic barriers with order parameters remains valid in the deep glass regime, even at astronomical timescales.
• This scaling persists despite a thermodynamic and structural crossover near the kinetic vitrification point.
• Experimental data up to nearly 20 decades in timescale show good agreement with the theory.

Conclusions:

• The robustness of the theoretical scaling suggests ultraslow dynamics are causally linked to medium-range structural order.
• The findings challenge the notion of a crossover from super-Arrhenius to Arrhenius relaxation at the glass transition temperature.
• The study opens new avenues for experimental and theoretical research in the deep glass regime.