The relaxation dynamics and thermodynamic properties of supercooled and glassy gambogic acid are investigated using both theory and experiment. We measure the temperature dependence of the relaxation times in three polymorphs (alpha-, beta-, and gamma-form). To gain insight into the relaxation processes, we propose a theoretical approach to quantitatively understand nature of these three relaxations. The alpha-relaxation captures cooperative motions of molecules while the beta-process is mainly governed by local dynamics of a single molecule within the cage formed by its nearest neighbors. Based on quantitative agreement between theory and experimental data, our calculations clearly indicate that the beta-process is a precursor of the structural relaxation and intramolecular motions are responsible for the gamma-relaxation. Moreover, the approach is exploited to study effects of the heating process on alpha relaxation. We find that the heating rate varies logarithmically with Tg and 1000/Tg. These variations are qualitatively consistent with many prior studies.
تحميل البحث