How Free Volume Does Influence the Dynamics of Glass Forming Liquids

Area of Science:

• Materials Science
• Physical Chemistry
• Statistical Mechanics

Background:

• Understanding the dynamics of glass-forming liquids is crucial for materials science.
• Existing models often struggle to capture relaxation behavior across diverse pressure-volume-temperature (PVT) conditions.

Purpose of the Study:

• To establish inverse free volume as a natural variable for analyzing relaxation data in glass-forming liquids.
• To develop a unified analytic expression for relaxation times valid over a broad PVT space.

Main Methods:

• Utilized pressure-volume-temperature (PVT) data and the Locally Correlated Lattice (LCL) equation of state to independently predict free volume.
• Analyzed experimental relaxation times (log τ) from eight glass-forming liquids across a wide PVT range.
• Plotted relaxation times against inverse free volume to observe isotherm behavior.

Main Results:

• Demonstrated that relaxation times (log τ) plotted against inverse free volume (1/V_free) yield a fan of linear isotherms.
• Showed that by incorporating a temperature function f(T) ∝ 1/T, these isotherms collapse into a single line with a system-dependent parameter 'b'.
• Established that log τ is a function of the combined variable 1/(V_freeT).

Conclusions:

• Inverse free volume is a natural and powerful variable for characterizing glass-forming liquid dynamics.
• Developed an explicit, analytic expression for log τ that accurately describes relaxation behavior across broad PVT conditions.
• The findings provide a new framework for understanding and predicting the thermophysical properties of glass-forming materials.