# Non-equilibrium Thermodynamics: Structural Relaxation, Fictive temperature and Tool-Narayanaswamy phenomenology in Glasses

## TL;DR

This paper develops a general non-equilibrium thermodynamic framework to understand structural relaxation in glasses, providing a theoretical basis for the concepts of fictive temperature and the Tool-Narayanaswamy phenomenology.

## Contribution

It formulates a comprehensive non-equilibrium thermodynamics approach to glasses, grounding the phenomenology of structural relaxation and fictive temperature in fundamental principles.

## Key findings

- Established a theoretical foundation for the fictive temperature concept.
- Derived the Tool-Narayanaswamy equation from thermodynamic principles.
- Provided insights into the relaxation processes in glasses.

## Abstract

Starting from the second law of thermodynamics applied to an isolated system consisting of the system surrounded by an extremely large medium, we formulate a general non-equilibrium thermodynamic description of the system when it is out of equilibrium. We then apply it to study the structural relaxation in glasses and establish the phenomenology behind the concept of the fictive temperature and of the empirical Tool-Narayanaswamy equation on firmer theoretical foundation.