Dielectric and electro-optical responses of a dielectrically negative nematic liquid crystal doped with cationic surfactant

Abstract

Cetyltrimethylammonium bromide (CTAB) was employed as an ionic dopant dispersed into a nematic liquid crystal characterized by its negative dielectric anisotropy. The electrohydrodynamic (EHD) effect in liquid crystal cells impregnated with various contents of CTAB was studied by dielectric spectroscopy and the corresponding electro-optical responses of the cells driven by an AC electric field were investigated. Compared with the undoped counterpart, the frequency range of the EHD regime after doping with 0.2-wt% CTAB into the liquid crystal was widened, and distinct optical textures, including dynamic scattering, stripes, and grids were unambiguously observed. The CTAB addition reduced the threshold voltage required for switching the planar state to other optical states generated by the EHD effect.