How to determine activation energy of glass transition

The article critically reviews the current methodologies for determination of apparent activation energy of structural relaxation, ?h*, in the glass transition range. Tool–Narayanaswamy–Moynihan phenomenological model was used to simulate data for all major types of relaxation behavior, which were consequently evaluated in terms of the tested methodologies (curve-fitting, evaluation of ?h* from intrinsic cycles and evaluation of ?h* from constant heating rate cycles). Advantages and disadvantages of particular methodologies are demonstrated and thoroughly discussed. In addition, effects of various data-distortive effects influencing determination of glass transition activation energy are demonstrated and described. The discussed data-distortive effects include presence thermal gradients, improperly designed temperature programs, incorrectly applied subtractions of the thermokinetic background, or inability of the DSC instrument to perform high cooling/heating rates. Detailed guide for correct determination of ?h* from DSC measurements is introduced.