State Key Laboratory of Metastable Materials Science and Technology and College of Materials Science and Engineering, Yanshan University, Qinhuangdao, Hebei 066004, China.
J Chem Phys. 2016 Dec 7;145(21):214501. doi: 10.1063/1.4968564.
Found in our recent dielectric study of a planar and rigid glass-former, 1-methylindole (1MID), is an unusual secondary relaxation unrelated in its dynamic properties to the structural α-relaxation. We speculated that it originates from the in-plane motion of the molecules, and the supposedly universal Johari-Goldstein (JG) β-relaxation with strong connection to the structural α-relaxation in rigid glass-formers is not resolved [X. Q. Li et al. J. Chem. Phys. 143, 104505 (2015)]. In this work, dielectric measurements are performed in binary mixtures of 1MID with two aromatics of weak polarity, ethylbenzene (EB) and triphenylethylene (TPE), in the highly viscous regimes near glass transition. EB and TPE have smaller and larger molecular sizes and glass transition temperatures T than 1MID, respectively. Strikingly, the results show that the resolved secondary relaxations of 1MID in the two mixtures share the same relaxation time and their temperature dependence as pure 1MID, independent of the mode and degree of dilution. The results indicate that the unusual secondary relaxation is not directly coupled with the α-relaxation, and support the in-plane-rotation interpretation of its origin. On the other hand, the supposedly universal and intermolecular JG β-relaxation coming from the out-of-plane motion of the planar molecule has weaker dielectric strength, and it cannot be resolved from the more intense in-plane-rotation secondary relaxation because the dipole moment of 1MID lies on the plane.
在我们最近对平面刚性玻璃形成体 1-甲基吲哚（1MID）的介电研究中发现了一种不寻常的次级松弛，其动力学特性与结构α松弛无关。我们推测它源于分子的面内运动，而在刚性玻璃形成体中与结构α松弛有强连接的普遍 Johari-Goldstein（JG）β松弛并未得到解决[X.Q. Li 等人，J. Chem. Phys. 143, 104505（2015）]。在这项工作中，在接近玻璃化转变的高度粘性区域中，对 1MID 与两种弱极性芳烃，乙基苯（EB）和三苯基乙烯（TPE）的二元混合物进行了介电测量。EB 和 TPE 的分子尺寸和玻璃化转变温度 T 分别小于、大于 1MID。引人注目的是，结果表明，两种混合物中 1MID 的分辨次级松弛具有相同的松弛时间和与纯 1MID 相同的温度依赖性，而与稀释的模式和程度无关。结果表明，这种不寻常的次级松弛与α松弛没有直接耦合，并且支持其起源的面内旋转解释。另一方面，来自平面分子的面外运动的普遍的和分子间的 JG β松弛具有较弱的介电强度，并且由于 1MID 的偶极矩位于平面上，因此无法从更强烈的面内旋转次级松弛中分辨出来。
