Dielectric Properties of Some Nematic Liquid Crystals with Strong Positive Dielectric Anisotropy

Measurements of the temperature dependence of the dielectric constants ε‖, ε⊥, and εis of some nematic liquid crystals with strong positive dielectric anisotropy (ε‖ ≃ 3 ε ⊥) are reported. The low frequency dispersion regions of the dielectric constants parallel to the unique axes were measured to be in the range from 10 kHz to 10 MHz. A correlation between the lengths of similar molecules and their relaxation frequency in the nematic state was found. The height of the potential barrier which hinders the reversal of the rodlike molecules in the nematic order was determined by measuring the temperature dependence of the low frequency relaxation and comparison with the temperature dependence of viscosity.