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.

通过使用短脉冲激光的热释电技术，研究了向列相和近晶相液晶中的宏观偏振，例如自发偏振、表面偏振和挠曲偏振。已经提出了一种用于评估激光照射时液晶单元中的温度变化的新技术，该技术基于温度变化时的双折射变化。使用这种温度估计技术，可以高精度地估计表面和挠曲电极化的大小和符号。还测量了这些极化的温度依赖性。在垂直排列的5CB电池中，发现表面极化从块体指向基底，即5CB分子的烷基取代基指向基底，这与二次谐波产生测量估计的结果相反。此外，垂直界面处的表面极化强度远小于从分子中完全排列的偶极矩理论上计算出的极化强度。这些结果表明四极有序参数的空间分布在表面偏振中起着重要作用。已评估了 5CB、8OCB 和 MBBA 的挠曲电系数的大小和符号。 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方向的差异。