Thermokinetic Description of the Heat Capacity Change at the Glass Transition: 1. Can Glass Transition Kinetics Be Adequately Described by a Single Activation Energy? 2. Can the Glass Transition Temperature Be Predicted from Basic Physical Parameters

By coupling nonequilibrium thermodynamics with solid-state kinetics, a description of the heat capacity (<i>c</i>_P) evolution as a function of the temperature (<i>T</i>) is derived that can be used to supplant commonly used empirical models. In addition to accurately describing the characteristic sigmoidal shape in the vicinity of the glass transition temperature (<i>T</i>_g), the proposed equation predicts a relaxation enthalpy peak to arise when either the enthalpy change of system relaxation is large or when the relaxation rate is fast. Such thermal events are often detected for amorphous compounds that have been annealed or stored for extended times. The activation energy of relaxation (<i>E</i>) is readily determined using different heating rates. Lastly, simple relationships are put forth to demonstrate the utility of <i>c</i>_P in predicting both <i>T</i>_g and the empirical parameter, <i>B</i>, in the Vogel-Fulcher-Tammann (VFT) equation widely used to describe primary relaxation in glasses.