# Determination of the entropy production during glass transition: theory and experiment

## TL;DR

This paper combines theoretical modeling and calorimetric experiments to quantify entropy production during glass transition, confirming the positive entropy production and the validity of thermodynamic principles like the Clausius theorem.

## Contribution

It introduces a statistical two-level system model for entropy production and experimentally measures entropy generation during glass transition using calorimetry.

## Key findings

- Entropy production during glass transition is positive and measurable.
- Thermodynamic cycles satisfy the Clausius theorem.
- Entropy production is a small percentage of the total configurational entropy.

## Abstract

A glass is a non-equilibrium thermodynamic state whose physical properties depend on time. Glass formation from the melt, as well as the inverse process of liquid structural recovery from the glass are non-equilibrium processes. A positive amount of entropy is produced during such irreversible processes. In this paper, we address the issue of the determination of entropy production during glass transition. Firstly, we theoretically determine the entropy production by means of the statistical model of a two-level system coupled to a master equation driving the time dependency of the occupancy probability of each state. Thermodynamic cycles of the type liquid-glass-liquid are considered in order to test the validity of the Clausius theorem. Secondly, we determine experimentally the production of entropy from differential scanning calorimetry experiments on the PolyVinylAcetate glass-former. Aging experiments are also considered. From the data treatments proposed here, we are able to determine the rate of production of entropy in each part of the experiments. Although being on the order of few % or less of the configurational entropy involved in the glass formation, the positive production of entropy is clearly determined. For all the thermodynamic cycles considered in these calorimetric experiments, the Clausius theorem is fulfilled.