Isomorph theory of physical aging.
1Glass and Time, IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark.
The Journal of Chemical Physics
|April 23, 2018
Summary
This study introduces systemic temperature (Ts) for aging R-simple systems, defining an aging phase diagram. This framework predicts aging behavior under various thermodynamic changes in glass-forming liquids.
Area of Science:
- Physics
- Physical Chemistry
- Materials Science
Background:
- Physically aging systems, particularly glass-forming liquids, exhibit complex dynamics deviating from equilibrium.
- Existing effective temperature concepts in glass science have limitations in describing non-equilibrium states.
Purpose of the Study:
- To derive and discuss the configuration-space Langevin and Smoluchowski equations for physically aging R-simple systems.
- To introduce a novel "systemic temperature" (Ts) applicable to any system configuration, regardless of equilibrium proximity.
- To establish an aging phase diagram based on density and systemic temperature.
Main Methods:
- Derivation of the configuration-space Langevin equation for aging R-simple systems.
- Formulation of the corresponding Smoluchowski equation.
- Definition and application of systemic temperature (Ts) as a function of density and potential energy.
- Analysis of aging dynamics under thermodynamic variable jumps.
Main Results:
- The systemic temperature (Ts) is defined as the equilibrium temperature corresponding to the system's instantaneous density and potential energy.
- In equilibrium, Ts approximates bath temperature (T), with fluctuations vanishing in the thermodynamic limit.
- An aging phase diagram is constructed using density and systemic temperature, illustrating the system's trajectory.
- The theory predicts aging behavior following various density-temperature and pressure-temperature jumps.
Conclusions:
- The proposed theory provides a unified framework for describing physically aging R-simple systems.
- The systemic temperature offers a more general approach than existing effective temperatures for non-equilibrium states.
- The theory implies a dynamic Prigogine-Defay ratio of unity for R-simple glass-forming liquids.
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