Strong modulation of electric permittivity at an isotropic-nematic phase transition in a liquid crystal mixture for optical devices based on the Kerr effect

Abstract

We report dielectric and electro-optical characteristics of a new bicomponent mixture, which at room temperature exhibits an isotropic phase. The mixture is based on the commonly known 4-Cyano-4′-pentylbiphenyl (5CB) compound and its structural homologue with a fluorine atom substituted laterally at a rigid molecular core. Due to a potential application of the studied mixture for optical devices based on the Kerr effect, the extensive study of the dielectric and optical properties of investigated mixture was done in a vicinity of an isotropic to a nematic phase transition. The investigated mixture is characterized by a large dielectric pretransitional effect. Under an electric field in the isotropic phase, a paranematic phase with a strong DC-modulation of electric permittivity was observed. Moreover, an unexpected increase of electric permittivity was observed exactly at clearing temperature. This behaviour was confirmed by an electro-optical observation. Relaxation processes at the phase transition are discussed and their parameters for pure compounds and the bicomponent mixture were calculated and analyzed. All experimental results are compared with observations obtained for the pure 5CB compound as a reference.