Thermodynamics of Supercooled Liquids and their Glass Transition

The thermodynamic properties of supercooled liquids are discussed and a phenomeno-logical model, capable of representing the most important experimental features, is presented. The most characteristic feature is the gradual decrease in entropy, by which the entropy of the liquid approaches that of a crystalline solid on cooling. This behaviour is modeled by means of defects, connected with the individual atoms, which are introduced to an “ideal” amorphous solid on heating. It is suggested that the increase in defect content yields not only an increase in enthalpy but also an extra increase in entropy. A tentative value ΔS = R, the gas constant, per mole of defects is suggested. The relation between glass-transition temperature and melting point is discussed under the assumption that the glass transition occurs at a certain critical defect content. Physical interpretations of the new model are discussed. The anomalous behaviour of liquid high-purity SiO2 is discussed. Finally, liquid Sn and glycerol are analyzed in terms of the model.