THE ORIENTATION-DEPENDENT INTERACTION ENERGY AS STUDIED BY THE POLARIZABILITY ANISOTROPY ANALYSIS

分子的不对称性是所有液晶物质的共同特征。与中生核相连接的软尾或间隔体往往沿场的导向器呈延长的构象。分子的极化率各向异性使分子间的伦敦引力呈现各向异性，从而有利于分子间的平行排列。对于REGID棒，我们可以通过去极化瑞利散射(DRS)的测量来解释极化张量的各向异性部分。对于仅在各向异性环境下定向的柔性链，不能使用相同的技术。假设在各向异性状态下允许的构象是已知的，则可以通过沿链假定键的可加性规则来计算这些柔性链的极化率各向异性。正如我们在另一项工作中所证明的那样，后一种信息可以通过使用重离子核磁共振技术来获得。1986财政年度，我们实验室安装了一台商用DRS设备，对过滤系统进行了轻微的改进。在接下来的一年里，对一系列二肽进行了光学各向异性测量。从而测试了该仪器的可靠性极限。对PAA和MBBA等典型介晶化合物也进行了测量。最后，根据上述步骤估算了氰基联苯核和正构烷基尾的化合物NCB的极化率各向异性。研究发现，柔性尾巴的贡献是巨大的。对于n=5和n=8的体系，所得结果与在向列相-各向同性转变温度的各种热力学性质中观察到的奇偶效应是一致的。因此，我们在这项工作中采用的方法论被证明是有用的。

Molecular asymmetry is a feature common to all liquid crystalline substances. Soft-tails or spacers joined with a mesogenic core tend to take extended conformations along the director of the field. The polarizability anisotropy of molecules causes the intermolecular London attractions to be anisotropic, with the results the parallel intermolecular alignment is favored. For regid rods, we can elucidate the anisotropic part of the polarizability tensor from the depolarization Rayleigh scattering (DRS) measurements. The same technique cannot be used for the flexible chains which orient only under the anisotropic environment. The polarizability anisotropy of these flexible chains may be calculated by assuming the bond-additivity rule along the chain, provided that the conformations permitted in the anisotropic state are known. As we have demonstrated in a separate work, the latter information can be obtained by using the deuterium NMR technique.In fiscal 1986, a commercial DRS apparatus, modified slightly in the filtering system, was installed in our laboratory. In the following year, the optical anisotropy measurements were carried out for a series of dipeptides. The limit of thereliability of the apparatus was thus tested. Measurements were also performed for some typical mesogenic compounds such as PAA and MBBA. Finally, the polarizability anisotropy of nCB, a compound comprising cyanobiphenyl core and n-alkyl tail, was estimated according to the procedure described above. Contribution from the flexible tail was found to be substantial. The results obtained for the system with n=5 and 8 are consistent with the odd-even effect observed in various thermodynamic properties at the nematic-isotropic transition temperature. The mothodology we have abopted in this work was thus proved to be useful.