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Liquid Crystals and their Application
Russian Journal

Zhidkie kristally i ikh prakticheskoe ispol'zovanie

Жидкие кристаллы и их практическое использование

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Rus Eng


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Zhidk. krist. ikh prakt. ispol'z. = Liq. Cryst. and their Appl., 2018, 18 (1), 24—29.
DOI: 10.18083/LCAppl.2018.1.24

Through Conductivity Effect on the Low-Frequency Dielectric Polarization of Liquid Crystals

U. M. Mallaboev, V. I. Novoselov

Author affiliations
Tyumen Industrial University, Tobolsk Industrial Institute (subsidiary),
5 Zona Vuzov St., Tobolsk, 626158, Russia. 

The low-frequency dispersion of the complex dielectric permittivity of nematic liquid crystals in the frequency range of 10–105 Hz and in the temperature range covering the nematic and isotropic phases was investigated. The objects of the study are nematic liquid crystals with both the positive and negative dielectric anisotropy: 4-n-amyl-4'-n-hexoxy α-cyanostilben, 4-cyanophenyl ether of 4'-n-octyloxybenzoic acid, 4-heptyloxy-4'-cyanostilben. A schematic diagram of the experimental apparatus for investigating the through conductivity of liquid crystal substances is presented. As it follows from the experimentally obtained dependences of the complex dielectric permittivity, for all studied nematic liquid crystals the dielectric permittivity at medium frequencies (ωτ < 1) has an equilibrium value, that is ε', ε''(tgδ) practically do not depend on frequency ν. At low frequencies of the electric field (ωτ << 1) a significant increase of the dielectric permittivity εeff. and dielectric loss-angle tangent tgδ was observed. It was established that the increase of εeff. and tgδ at low frequencies of the electric field is caused by the through electric conductivity effect. The dependence of the through electric conductivity on temperature in nematic and isotropic phases was studied. The ways of eliminating the contribution of the through conductivity to the complex dielectric permittivity of liquid crystals at low frequencies is discussed.

Keywords: dielectric conductivity of liquid crystals, low-frequency dispersion, through electric conductivity of liquid crystals

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