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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

本研究发展了一套新的动态光散射光谱和非线性介电弛豫光谱测量系统。我们将该系统应用于铁电和反铁电液晶，并获得了它们的结构，相变和动力学的各种重要信息。我们测量了铁电液晶近晶C_* 相Goldstone模散射光的相关频率色散。通过与唯象理论的比较，得到了弹性常数与粘度之比和螺距随温度的变化关系。当施加垂直于螺旋轴的直流电场时，在色散曲线中观察到频率间隙，其波数接近螺旋波数的一半，并且发现差距随场强线性增加。我们检测到戈德斯通的动力学变化 ...更多信息由均匀螺旋结构到孤子晶格的结构变化引起的模式。利用NDRS研究了反铁电液晶各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Goldstone模式的动力学行为可以通过非线性谱检测到。研究了近晶A相到其它近晶相的非线性介电常数在临界点附近的临界行为，并根据朗道型唯象理论讨论了临界指数和介电常数的符号。从SmA相的非线性介电常数和电斜常数的实验观测值计算了自由能密度中的唯象系数，并讨论了这些值与化学结构之间的关系。总之，我们利用新开发的测量系统获得了铁电和反铁电液晶的各种信息。少