Dielectric Relaxation in Liquid Crystalline Mixture Based on Cyanophenylpyridines

Abstract
Dielectric properties of nematic liquid crystal mixture ZhK-1630A were investigated in the frequency range of 10 ÷ 10⁸ Hz and temperature range of –10 ÷ 90 °С. On the basis of the Debye’s relaxation polarization model, dielectric spectra of the temperature dependence of the orientational relaxation time τ were numerically approximated at the parallel orientation of the molecular director relatively to the alternating electric field. The activation energy of the relaxation process of the rotation of molecules around their short axis was measured in the temperature interval of –10 ÷ 15 °С in which a dispersion of the longitudinal component of the dielectric constant takes place. The energy of potential barrier for polar molecules rotation in the mesophase was calculated. The values of the molecular friction coefficient and rotational diffusion coefficient were obtained by different methods. The experimental data obtained are in satisfactory agreement with the existing theoretical models.

Keywords: dielectric spectroscopy, molecular friction coefficient, rotational diffusion coefficient