Effects of ion doping on the dielectric and electro-optical properties of chiral nematic liquid crystal

Abstract

This study presents experimental findings pertaining to the use of the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a dopant dispersed in cholesteric liquid crystal. The impact of the additive on the electrical and dielectric properties was investigated by dielectric spectroscopy. Compared with that in the pure counterpart, the dielectric relaxation frequency increased due to the added ions in the cholesteric liquid crystals impregnated with 0.01–0.5-wt% CTAB. Furthermore, by analyzing the dielectric spectra in a specific frequency range, the DC conductivity, ion density, and diffusion coefficient were calculated and compared. By fitting the experimental data into the Arrhenius equation, the activation energy was obtained as well. Our experimental results illustrated that all these physical properties were strongly dependent on the CTAB concentration and the temperature. This work also involved the electro-optical measurement in combination with the observation of optical texture. The ion addition provoked electrohydrodynamic flows in a surfactant-dispersed mixture, generating a homogeneous and transparent uniform lying helix state between two low-transmission optical states—the focal conic and dynamic scattering states. The operating frequency range of the dynamic scattering state was significantly broadened by the ionic dopant.