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

分子不对称是所有液晶物质的共同特征。软尾或间隔层与中生岩心连接，趋向于沿场方向呈延伸构象。分子极化率的各向异性使分子间的伦敦引力具有各向异性，有利于分子间的平行排列。对于栅极棒，我们可以通过去极化瑞利散射（DRS）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取向的柔性链，不能采用相同的方法。在已知各向异性状态下允许的构象的情况下，可以通过假设沿链的键加性规则来计算这些柔性链的极化各向异性。正如我们在另一项工作中所证明的那样，后者的信息可以通过使用氘核磁共振技术获得。在1986财政年度，我们的实验室安装了一个商业DRS设备，对过滤系统进行了轻微修改。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。这样就测试了仪器的可靠性极限。对PAA、MBBA等典型介生化合物也进行了测定。最后，根据上述方法估计了由氰基苯核和正烷基尾组成的化合物nCB的极化各向异性。研究发现，柔性尾巴的贡献是巨大的。当n=5和8时，得到的结果与向列-各向同性转变温度下各种热力学性质的奇偶效应一致。因此，我们在这项工作中采用的方法被证明是有用的。

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.