THROUGH CONDUCTIVITY EFFECT ON THE LOW-FREQUENCY DIELECTRIC POLARIZATION OF LIQUID CRYSTALS

The low-frequency dispersion of the complex dielectric permittivity of nematic liquid crystals in the frequency range of 10-10(5) 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 alpha-cyanostilben, 4-cyanophenyl ether of 4'-n-octyloxybenzoic acid, 4-heptyloxy4'-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 (omega tau < 1) has an equilibrium value, that is epsilon', epsilon ''(tg delta) practically do not depend on frequency nu.At low frequencies of the electric field (omega tau << 1) a significant increase of the dielectric permittivity epsilon(ff). and dielectric loss-angle tangent tgd was observed. It was established that the increase of (epsilon eff). and tgd 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.