Nonlinear Relaxation Spectroscopy of Fluctuation in the Ferroelectric and Antiferroelectric Liquid Crystals

铁电和反铁电液晶涨落的非线性弛豫谱

基本信息

批准号：
06452137
负责人：
HAYAKAWA Reinosuke
金额：
$ 4.35万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

We developed in this research a new measurement system for the dynamic light scattering spectroscopy and the nonlinear dielectric relaxation spectroscopy (NDRS) for a wide frequency range. We applied the system to the ferroelectric and antiferroelectric liquid crystals and obtained a variety of important information on their structures, phase transitions and dynamics. We measured the dispersion of the correlation frequency of the scattered light for the Goldstone mode in the Smectic C_* phase of the ferroelectric liquid crystals. By comparison with the phenomenological theory, we obtained the temperature dependences of the ratio of the elastic constant to the viscosity and the helical pitch. When the dc electric field was applied perpendicular to the helical axis, a frequency gap was observed in the dispersion curve at a wavenumber nearly half of the helical wavenumber and the gap was found to increase linearly to the field strength. We detected the change in the dynamics of Goldstone … More mode induced by the structural change from the uniform helical structure to the soliton lattice. The dynamical properties characteristic of various smectic phases of antiferroelectric liquid crystals were investigated by NDRS.It was found that the dynamics of the antiferroelectric Goldstone mode undetectable by the linear dielectric spectrum was detected by the nonlinear spectrum. The critical behavior in the nonlinear dielectric constant near the critical points from the Smectic A to other smectic phases was studied and the critical exponent and sign of the constant were discussed in terms of phenomenological theory of Landau type. The phenomenological coefficients in the free energy density were evaluated from the nonlinear dielectric constants and the electroclinic constant experimentally observed for the SmA phase and the relation between these values and the chemical structure was also discussed. In conclusion, we obtained various kinds of information on the ferroelectric and antiferroelectric liquid crystals by using the newly developed measurement system. Less

我们在这项研究中开发了一种新的宽频率范围的动态光散射光谱和非线性介电弛豫光谱（NDRS）测量系统，我们将该系统应用于铁电和反铁电液晶，并获得了有关它们的各种重要信息。我们测量了铁电液晶近晶 C_* 相中戈德斯通模式的散射光相关频率的色散。根据唯象理论，我们得到了弹性常数与粘度之比和螺距的温度依赖性。当垂直于螺旋轴施加直流电场时，在色散曲线中在波数接近一半处观察到频率间隙。我们发现螺旋波数和间隙随场强线性增加，我们检测到由均匀螺旋结构到均匀螺旋结构的结构变化引起的戈德斯通模式动力学的变化。利用NDRS研究了反铁电液晶的各种近晶相的动力学特性，发现线性介电谱无法检测到的反铁电戈德斯通模式的动力学可以通过临界点附近的非线性介电常数来检测。研究了从近晶A到其他近晶相的变化，并根据下式讨论了常数的临界指数和符号：朗道型唯象理论。根据实验观察到的 SmA 相的非线性介电常数和电斜常数来评估自由能密度的唯象系数，并讨论了这些值与化学结构之间的关系。通过使用新开发的测量系统，我们获得了有关铁电和反铁电液晶的各种信息。