MOLECULAR ORIENTATIONAL CORRELATION AND ORIENTATIONAL GLASS IN PLASTIC CRYSTAL

在塑性相中，1-氰基金刚烷C10 H15 CN具有位置顺序和重取向，<001>并且其等价的五个取向（<001>六重重取向）围绕偶极轴旋转（单轴旋转）。在从塑性相缓慢冷却时，化合物转变为亚稳相，然后转变为有序相。六<001>重取向和单轴旋转冻结在有序相。在玻璃化转变温度T_g=170 K以下，塑性相的分子可以通过淬灭容易地获得玻璃相。在玻璃相，<001>六重取向冻结，分子随机采取六个取向之一，围绕偶极轴旋转。在这项研究中，塑性相，玻璃相和亚稳相已经通过核磁共振和分子动力学模拟研究，以澄清玻璃形成的起源。<13>13 C NMR清楚地表明，分子<001>在塑性相中经历了六次重取向，在塑性相中经历了<111>八次重取向， ...更多信息 醚在亚稳相中具有六重取向，。此外，亚稳相被发现向有序相弛豫。结构弛豫时间为3200 s。在气相中，自旋-晶格弛豫时间反映了单轴转动的关联时间分布。通过假定Davidson-Cole函数，确定了运动分布的参数β为0.2。分子动力学模拟表明，即使在塑性阶段，六重取向的相关时间也是多色散的。计算的相关函数的六倍重取向进行了分析，在几个温度下，通过使用拉伸指数函数。结果表明，β随温度的降低而增大。从频散曲线的分析可知，运动分布的产生主要是由于相关时间的频散。此外，随着温度的降低，分散变得显著。色散的温度行为与β的温度行为基本一致。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