The Third Principle of thermodynamics and the zero-point entropy of glasses: History and new developments

A survey is given on the historical development of ideas, concerning the Third Principle of thermodynamics and the thermodynamic nature of glasses. The classical thermodynamic approach of Nernst, Einstein and Planck is given in its development together with the way thermodynamics of irreversible processes is treating the kinetics of glass-transition. It is shown that both these classical ideas and the generic application of non-equilibrium thermodynamics determine the non-zero value of the zero-point entropy of glasses and the value of the other frozen-in thermodynamic functions of glass, their dependence on cooling rate and on glass structure. For many years glass science was governed by ideas, formulated 80 years ago by F. Simon: glasses as non-equilibrium, non-thermodynamic systems do not obey the classical requirements of the Third Principle. It is shown here that in fact glasses and most probably any other frozen-in systems, every non-equilibrium body, follow the Third Principle, although in a particular way. In glasses a considerable amount of configurational entropy is frozen-in and this statement is confirmed by experiment. The frozen-in value of the configurational entropy, determining substantially the properties of a glass, does not prevent vitrified systems to follow the requirements of a sufficiently generally formulated version of the Third Principle (different from the formulation commonly assigned to Planck), in the same way as matter in non-equilibrium states follows the requirements (again in a specific way) of both the Second and the First Principles of thermodynamics. It is shown, that calorimetric determinations, vapor pressure measurements, dissolution kinetics, the analysis of volume properties and the viscosity course upon vitrification directly demonstrate the existence of a frozen-in configurational entropy of glasses and its dependence on the vitrification kinetics.