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

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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