Activation volume in superpressed glass-formers.

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• In pressurized glass-forming systems, apparent activation volume (V_a(P)) governs structural relaxation and viscosity.
• Current models often assume V_a(P) equals the structural volume (V^#(P)).

Purpose of the Study:

• To investigate the relationship between apparent activation volume (V_a(P)) and structural volume (V^#(P)) in pressurized glass formers.
• To propose a simple, non-biased method for determining V_a(P) and its parameterization.
• To explore the estimation of absolute stability limits for pressure and volume.

Main Methods:

• Analysis of Super-Barus behavior relating relaxation time (τ) or viscosity (η) to pressure (P).
• Comparison of V_a(P) with V^#(P) under varying pressure conditions, particularly approaching the glass pressure (P_g).
• Development and application of a new methodology for V_a(P) determination and parameterization.

Main Results:

• Demonstrated that V_a(P) is significantly smaller than V^#(P) as pressure approaches the glass pressure (P_g).
• Identified that V_a(P) and V^#(P) only coincide under basic Barus dynamics (constant V_a) or at zero pressure.
• Proposed a new relation for V_a(P) parameterization, similar to the Murnaghan-O'Connel equation used in deep Earth studies.

Conclusions:

• The assumption V_a(P) = V^#(P) is invalid for pressurized glass formers near P_g.
• The developed methodology provides a straightforward way to determine V_a(P) and offers insights into material stability.
• The findings are applicable to diverse materials including liquids, liquid crystals, and epoxy resins.