Pre-transitional Phenomenon of Nematic-smectic Phase Transition Observed by Elastic Constant - Observation of Frederiks Transition by Forced Rayleigh Scattering -

通过弹性常数观察到的向列-近晶相变的预转变现象 - 通过受迫瑞利散射观察 Frederiks 相变 -

基本信息

批准号：
60540199
负责人：
TAKEZOE Hideo
金额：
$ 1.02万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

项目摘要

The elastic constants of liquid crystals are usually determined by detecting the critical field where the reorientation starts to occur by applying an electric or a magnetic field (Frederiks transition) perpendicular to the alignment direction. As for the twist elastic constant <K_(22)> , however, usual methods for determining the elastic constants <K_(11)> and <K_(33)> for splay and bend deformations can not be used. The first purpose of the present study was to construct the system for determining <K_(22)> by means of forced Rayleigh scattering.For this purpose, we examined and improved our forced Rayleigh scattering system itself by extending the diffusion measurements in nematics to in smectic A and smectic B phases and by investigating the temperature dependence of the signal intensity. We have also constructed the system of the forced Rayleigh scattering in a magnetic field. It was confirmed by using the standard material, 5CB, that the relaxation time of the diffraction in tensi … More ty from the transient grating starts to change at the critical field strength. This fact means that the diffusion constant changes due to the magnetic field induced reorientation. The elastic constant <K_(22)> was determined by the critical field. The results obtained agreed with the recent results by other techniques.To accomplish the final purpose of the present study, i.e., observation of the critical phenomenon, we carried out the preliminary measurements on 8CB. The increase of <K_(22)> was observed within the temperature range of 1 degree from the nematicsmectic A phase transition temperature, although the quantitative measurements such as the critical exponent have not been done. Since the difficulty of the quantitative measurements is due to the poor temperature control, the improvement is now under consideration. Thus it is a valuable result that the <K_(22)> measurements is now easily performed by forced Rayleigh scattering, although the final goal of the present work has not been reached. Less

液晶的弹性常数通常是通过施加垂直于取向方向的电场或磁场（弗雷德里克转变）来检测开始发生重新取向的临界场来确定的。至于扭转弹性常数<K_(22)>。然而，不能使用确定张开变形和弯曲变形的弹性常数<K_(11)>和<K_(33)>的常用方法。构建通过强制瑞利散射确定<K_(22)>的系统。为此，我们通过将向列相中的扩散测量扩展到近晶A和近晶B相并通过研究来检查和改进我们的强制瑞利散射系统本身我们还构建了磁场中的受迫瑞利散射系统，并使用标准材料 5CB 证实了衍射的弛豫时间。瞬态光栅的张力在临界场强度处开始变化，这意味着扩散常数由于磁场引起的重新取向而发生变化。弹性常数<K_(22)>由临界场结果确定。为了实现本研究的最终目的，即观察临界现象，我们对8CB进行了初步测量，观察到了<K_(22)>的增加。温度范围与向列相A相变温度相差1度，虽然尚未进行临界指数等定量测量，但由于温度控制不佳导致测量困难，因此目前正在考虑改进。有价值的结果是，尽管目前工作的最终目标尚未达到，但现在可以通过强制瑞利散射轻松执行<K_(22)>测量。