Dielectric Study of the Electric-Field-Induced Critical Endpoint in a Nematic Liquid Crystal with Positive Dielectric Anisotropy

Nematic liquid crystals with positive dielectric anisotropy exhibit a critical endpoint under the electric field. In particular, isotropic-nematic phase transition may disappear at a critical endpoint under external factors such as an electric field. We investigate the dielectric properties near the critical endpoint both theoretically and experimentally. First, we calculate the dielectric constant under an electric field according to the Landau de Gennes theory to show that the soft mode related to the isotropic-nematic phase transition can be revealed by dielectric measurements. Temperature dependence of the dielectric constant of 8CB nematic liquid crystal is measured under the DC electric field. We have successfully observed a low-frequency relaxation mode corresponding to the soft mode near the critical point. This shows the feasibility of the soft mode observation near the critical point in the future on the basis of temperature and electric field dependences of the relaxation strength and frequency using an improved measurement system.