Rheo-dielectric behavior of low molecular weight liquid crystal 2. Behavior of 8CB in nematic and smectic states

Rheo-dielectric behavior was examined for 4-4'-n-octyl-cyanobiphenyl (8CB) having large dipoles parallel to its principal axis (in the direction of the C=N bond). In the quiescent stare at all temperatures (T) examined, orientational fluctuation of the 8CB molecules was observed as dielectric dispersions at characteristic frequencies omega(c) > 10(6) s(-1). In the isotropic state at high T, no detectable changes of the complex dielectric constant epsilon* (omega) were found under slow flow at shear rates (gamma)over dot much less than omega(c). In the nematic state at intermediate T, the terminal relaxation intensity of epsilon* (omega) was decreased under such slow flow. In the smectic state at lower T, the flow effect became much less significant. These results were related to the flow-induced changes of the liquid crystalline textures in the nematic and smectic states, and the differences of the rheo-dielectric behavior in these states are discussed in relation to a difference of the symmetry of molecular arrangements in the nematic and smectic textures.