Fictive temperatures of pharmaceutical glasses—A comparison of two methods for determining the enthalpy and entropy integrals

Fictive temperature of a glass, image is determined by matching the Cp dT integrals in a single DSC heating scan (method I), a method also useful for determining the fictive temperature image by matching the Cp dln T integrals. But for quench-formed glasses, the heating scan contains a broad minimum that prevents one from determining image and image by method I. Therefore, an additional heating scan is used for the purpose (method II). For some quench-formed glasses, method II has yielded image considerably different from image, causing concerns on the use of the method and on the conclusions on the entropy of glass. To resolve it, we use method II to determine image and image of normally formed and annealed glasses of acetaminophen, carbamazepine and griseofulvin, and find that both the image and image values are identical to the values obtained by using method I. This confirms that the entropy production on the liquid–glass path is too small to affect the residual entropy of glass. Contribution from dynamically heterogeneous, β or JG relaxation is not observed for these low-energy glasses. The difference between image and image previously observed for quench-formed glasses is due to data errors and/or extrapolation.