Thermodynamic aspects of the glass transition in liquids and plastic crystals

We outline the basic phenomena characterizing the glass transition, highlighting the intimate association of thermodynamic changes and relaxation times, and the limits set by the Kauzmann entropy crises. The relation between the Kauzmann temperature and the glass transition temperature is examined in relation to the strong and fragile classification of liquids, and a consistency between the parameters of the normalized Vogel- Fulcher equation and the purely thermodynamic Kauzmann temperature is demonstrated. The separate roles of kinetic and thermodynamic factors in establishing the strong and fragile pattern are analyzed and the apparently anomalous position of the alcohols in the scheme is accounted for in these It is well recognized that the glass transition, as it is observed experimentally, is a kinetic phenomenon. It is simply the consequence of the rapidly increasing time scale for structural equilibration of the supercooling liquid crossing the time scale of the experiment being used to study the substance.(l) While the phenomenon itself is clearly under kinetic Control, the thermodynamic consequences of the "falling out of equilibrium" are highly significant and are of much intrinsic interest for liquid state understanding. These changes and the analysis of their significance provide the basis for this lecture.