基于位形熵模型的山梨醇玻璃焓松弛的量热分析

利用DSC技术考察了无定形山梨醇体系的焓松弛行为,在10 K·min-1的升温速率下测定了经历不同降温速率(0.5～20 K·min-1)的山梨醇在玻璃化转变(T8)前后的比热容Cp(T)].利用基于位形熵演变的焓松弛现象学模型(GR模型)模拟了实验数据.不论是否假设松弛过程存在一个亚稳极限态,模型参数均能很好地重现...

Calorimetric Study on the Enthalpy Relaxation in Sorbitol Based on the Configurational Entropy Model

Enthalpy relaxation dynamics of amorphous D-sorbitol has been studied by differential scanning calorimetry (DSC). A series of specific heat capacity curves (c_p(T)) were measured on heating (10 K?min^－1) after cooling the sample at different rates ranged between 0.5 and 20 K?min^－1. A phenomenological model of enthalpy relaxation based on the evolution of configurational entropy (GR model) was used to simulate the experimental data. All the experimental traces can be fairly well reproduced by this model, no matter whether a metastable limit state of relaxation process is assumed. The physically reasonable model parameters seemed to be independent of thermal history, except the nonexponential parameter, which increased slightly as the cooling rate increasing. The model parameter sets obtained under lower cooling rates show better predictive ability than those obtained under higher ones. Since the calculated relaxation time value is strongly dependent on the “fixed parameter” value, the predictive ability to the c_p(T) curves is not the only criterion for the determination of relaxation time. Take the limit fictive temperature as T_g in the fragility calculation leads to an significantly smaller value than the published data.