MOLECULAR ORIENTATIONAL CORRELATION AND ORIENTATIONAL GLASS IN PLASTIC CRYSTAL

在塑性相中，1-氰基金刚烷C10H15CN具有位置有序性，并在绕偶极轴旋转(单轴旋转)的等价五个取向(&lt；001&gt；六重取向)之间重新定向。当从塑性相缓慢冷却时，化合物转变为亚稳态相，然后转变为有序相。六次重定向和单轴旋转在有序相中冻结。在玻璃化转变温度T_g=170K以下的塑料相中，分子淬火很容易得到玻璃相。在玻璃相中，-lt；001&gt；六重取向冻结，分子绕偶极轴旋转的六个取向中的任意一个。在本研究中，通过核磁共振和分子动力学模拟研究了塑性相、玻璃相和亚稳态相，以阐明玻璃形成的原因。核磁共振清楚地表明，分子在塑性相中经历了六次重取向，并经历了八次…重取向。更多的乙醚与亚稳相中的六重取向。此外，还发现亚稳态相向有序相松弛。结构弛豫时间确定为3200 S，在气相，自旋-晶格弛豫时间表明单轴转动的关联时间分布。通过假设Davidson-Cole函数，确定运动分布β的参数为0.2。分子动力学模拟表明，即使在塑性阶段，六次重定向的关联时间也是多频散的。利用拉伸指数函数分析了在不同温度下六次重定向的关联函数。结果表明，β随温度的降低而增大。从频散曲线分析可知，运动分布是由相关时间的频散引起的。此外，温度越低，分散性越明显。分散体的温度行为与β的温度行为基本一致。较少

In a plastic phase, 1-cyanoadamantane C10H15CN has a positional order and reorients among <001> and its equivalent five orientations (<001> six-fold reorientation) rotating around dipolar axis (uniaxial rotation). On cooling from the plastic phase slowly, the compound transforms to a metastable phase, and then to an ordered phase. The <001> six-fold reorientation and uniaxial rotation freezes in the ordered phase. A glassy phase can easily be obtained by quenching the molecules in the plastic phase below glass transition temperature T_g=170 K. In the glassy phase, the <001> six-fold reorientation freezes, the molecules take randomly one of the six orientations rotating around the dipolar axis. In this study, the plastic, glassy and metastable phases have been studied by NMR and MD simulation to clarify the origin of glass forming.^<13>C NMR shows clearly that the molecules undergo the <001> six-fold reorientation in the plastic phase, and undergo the <111> eight-fold reorientations tog … More ether with the six-fold reorientation in the metastable phase,. In addition, the metastable phase is found to relax toward the ordered phase. The structural relaxation time is determined to be 3200 s. In the gassy phase, the spin-lattice relaxation time tells that the correlation time of the uniaxial rotation distributes. By assuming Davidson-Cole function, the parameter for motional distribution β is determined to be 0.2. This means that the motion is largely poly-dispersive.The MD simulation shows that the correlation time of the six-fold reorientation is poly-dispersive even in the plastic phase. The correlation function calculated for the six-fold reorientation is analyzed at several temperatures by using a stretched exponential function. Obtained results show that β increases with decreasing temperature. From the analysis of dispersion curves, the motional distribution is fund to arise from the dispersion of the correlation time. Moreover, the dispersion becomes remarkable with decreasing temperature. The temperature behavior of the dispersion almost agrees with that of β. Less