Goitiandia L, Alegria A
Departamento de Fisica de Materiales, Universidad del Pais Vasco, Facultad de Quimica, 20080 San Sebastian, Spain.
J Chem Phys. 2004 Jul 15;121(3):1636-43. doi: 10.1063/1.1764493.
The temperature dependence of the alpha-relaxation time out of equilibrium has been investigated by means of dielectric relaxation in a series of fragile glass formers including several polymers. The influence of physical aging on this behavior has also been studied. The experimental results have been quantitatively compared with the predictions of the Adam-Gibbs equation. It has been found that, whereas for small molecule glass formers the experimental values of the apparent activation energy agree quite well with the prediction of the Adam-Gibbs equation, for polymers the experimental activation energy values are systematically higher. Moreover, whereas for small molecule glass formers the experimental values of the apparent activation energy remains essentially unaffected by physical aging, for polymers a pronounced reduction of the experimental apparent activation energy is observed. These results are found to be consistent with the Adam-Gibbs equation if a significant temperature variation of the configurational entropy in the investigated temperature range would occur for nonannealed polymers, being the possible variation hardly noticeable for the small molecules. With this assumption, all the obtained results would support the validity of the Adam-Gibbs equation for describing the temperature dependence of the time scale of the alpha-relaxation also out of equilibrium, at least for fragile glass formers.
通过介电弛豫方法，在包括几种聚合物在内的一系列易碎玻璃形成体中，研究了非平衡态下α弛豫时间的温度依赖性。还研究了物理老化对这种行为的影响。实验结果已与亚当 - 吉布斯方程的预测进行了定量比较。结果发现，对于小分子玻璃形成体，表观活化能的实验值与亚当 - 吉布斯方程的预测相当吻合，而对于聚合物，实验活化能值则系统地更高。此外，对于小分子玻璃形成体，表观活化能的实验值基本上不受物理老化的影响，而对于聚合物，观察到实验表观活化能明显降低。如果在所研究的温度范围内，未退火聚合物的构型熵会发生显著的温度变化，而小分子的这种可能变化几乎不明显，那么这些结果与亚当 - 吉布斯方程是一致的。基于这一假设，所有获得的结果将支持亚当 - 吉布斯方程对于描述非平衡态下α弛豫时间尺度的温度依赖性的有效性，至少对于易碎玻璃形成体是如此。
