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

在这项研究中，我们开发了一种新的测量系统，用于动态光散射谱和非线性介电弛豫谱(NDRS)的宽频带测量。我们将该系统应用于铁电和反铁电液晶，获得了关于它们的结构、相变和动力学的各种重要信息。测量了铁电液晶近晶C_*相中Goldstone模散射光的相关频率的色散。通过与唯象理论的比较，得到了弹性常数与粘性比和螺距的温度依赖关系。当外加垂直于螺旋轴的直流电场时，色散曲线在接近螺旋波数一半的波数处出现频隙，且该频隙与场强成线性关系。我们检测到了Goldstone…的动力学变化从均匀螺旋结构到孤子晶格的结构变化导致更多的模变。用NDRS研究了反铁电液晶中各种近晶相的动力学性质，发现线性介电谱无法探测到的反铁电Goldstone模的动力学特性被非线性谱所探测到。根据Landau型唯象理论，研究了从近晶相A到其他近晶相的临界点附近的非线性介电常数的临界行为，讨论了介电常数的临界指数和临界符号。由实验测得的SMA相的非线性介电常数和电倾斜常数估算了自由能密度的唯象系数，并讨论了它们与化学结构的关系。综上所述，我们利用新开发的测量系统获得了关于铁电和反铁电液晶的各种信息。较少

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