Effect of Annealing Conditions on Enthalpy Relaxation Parameters of <em>D</em>-Sorbitol Glass

Abstract

We studied the enthalpy relaxation dynamics of amorphous D-sorbitol by differential scanning calorimetry (DSC). A series of specific heat capacities (Cp(T)) for D-sorbitol were measured upon heating of 10 K·min-1. The samples were subjected to thermal treatment involving isothermal annealing with different annealing time (ta). A new phenomenological model by Gomez Ribelles (the GR model) of enthalpy relaxation based on the evolution of configurational entropy was used to simulate the experimental data to verify the applicability of the GR model to small molecular glass. The results indicated that a single set of GR model parameters only reproduced the corresponding experimental Cp(T) curve of D-sorbitol fairly well. It failed to find a set of GR model parameters as the material constant independent of the thermal history. In contrast with other phenomenological models, some parameters of the GR model remained unchanged. The model parameter sets obtained under longer annealing time show better predictive ability. In contrast to the continuous cooling process for D-sorbitol, the ratio between the mean value of the limit state parameter (δ) and the increment of specific heat capacity at Tg (△Cp(Tg)) apparently increases, but the increase is less than that of polymers. The results brought into question if the metastable limit state introduced by the GR model applied to small molecular glass systems.