Spontaneous Polarization and Chirality in Ferroelectric and Antiferroelectric Liquid Crystals

铁电和反铁电液晶中的自发极化和手性

基本信息

批准号：
12450012
负责人：
OZAKI Masanori
金额：
$ 9.09万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

Macroscopic polarizations in nematic and smectic liquid crystals such as a spontaneous polarization, surface polarization and flexoelectric polarization have been investigated by means of pyroelectric technique using a short pulse laser. A novel technique for an evaluation of a temperature change in a liquid crystal cell upon the laser light irradiation has been proposed, which is based on a birefringence change upon the temperature change. Using this temperature estimation technique, the magnitude and the sign of the surface and flexoelectric polarizations have been estimated with a high precision. The temperature dependence of these polarization has also been measured. In a homeotropically aligned cell of 5CB, it is found that surface polarization directs from a balk to substrate and, namely, the alkyl substituents of 5CB molecules point toward substrate, which is opposite result to that estimated from second harmonic generation measurement. In addition, the magnitude of the surface polarization at the homeotropic interface is much smaller than that theoretically evaluated from the completely aligned dipole moments in the molecules. These results indicate that the spatial distribution of the order parameter of quadrupole play an important role in the surface polarization. The magnitude and sign of flexoelectric coefficients for 5CB, 8OCB and MBBA have been evaluated. The sign for 5CB is negative, while that for 8OCB is positive. This discrepancy might originate from the difference of the direction of the permanent dipole moment in the molecule.

已经使用短脉冲激光器研究了nematic和近晶液体晶体中的宏观极化，例如自发极化，表面极化和柔韧性极化。已经提出了一种用于评估激光光照射时液晶细胞中温度变化的新技术，该技术基于温度变化时的双折射变化。使用此温度估计技术，估计了表面和挠性极化的幅度和符号。这些极化的温度依赖性也已经测量。在同型对齐的5CB的细胞中，发现表面极化从balk到底物，即5CB分子的烷基取代基指向底物，这与从第二次谐波产生测量中估计的结果相反。此外，同型界面处的表面极化的大小要比从分子中完全排列的偶极矩进行的理论上评估的幅度要小得多。这些结果表明，四极杆的空间分布在表面极化中起重要作用。已经评估了5CB，8OCB和MBBA的挠性系数的大小和符号。 5CB的符号为负，而8OCB的符号为正。这种差异可能源于分子中永久偶极矩的方向的差异。