Determination of the entropy production during glass transition: Theory and experiment

A glass is a non-equilibrium thermodynamic state whose physical properties depend on time. In this paper, we address the issue of the determination of entropy production during glass transition. In a first part, we simulate the entropy production rate of a two-level system departed from equilibrium by cooling. We show that this system, which can simulate the basic thermodynamic behavior of a glass-former, obeys the Clausius theorem. This first theoretical part shows us the importance of the fictive temperature in order to determine the entropy production rate. In a second part, we determine experimentally, with a high degree of precision, the entropy production rate of a polymer-glass, the Poly(vinyl acetate), during cooling/heating at different rates, and also during annealing steps at different aging times. Although being on the order of few %, or less, of the configurational entropy involved in the glass formation, the positive entropy generated over different parts of the cycle is clearly determined. These new data may open new insights for an accurate thermodynamic treatment of the glass transition.