Concentration fluctuations induced by orientation fluctuations in polybutadiene–4-cyano-4'-n-octylbiphenyl mixtures

Abstract

The changes in concentration fluctuations of polymer-liquid crystal (LC) binary mixtures with temperature were investigated by small-angle X-ray scattering in their one-phase region and in the isotropic state of the LC. The concentration fluctuations consist of two modes: an OZD mode expressed by the OrnsteinZernike-Debye equation with a correlation length and a DB mode expressed by the Debye-Buche equation with a correlation length l. The temperature dependence of the OZD mode exhibits critical phenomena similar to common binary mixtures. Under the condition where the LC molecules are oriented by an electric field, the OZD mode is insensitive to the orientation while the DB mode is enhanced perpendicular to the orientation direction. These results indicate that the DB mode is induced by the orientation of the LC molecules.