Rheological Properties and Texture of a Smectic Liquid Crystal

Abstract

The relationship between rheological properties and texture of a smectic-A liquid crystal, 4-cyano-4'-octylibiphenyl (8CB), was studied. The rheological measurements were carried out using the Rheometrics Fluids Spectrometer (RFSII) with a cone and plate geometry. We measured rheological properies such as steady shear viscosity, stress growth, and strage and loss moduli, G' and G” after various flow histories and observed the change of the texture under steady shear.
For the measurements without pre-shearing just after cooling from its isotropic phase, G' and G” showed the frequency dependence in the low frequency region. However, with applying pre-shearing after cooling, G' was almost constant irrespective of frequency, and the sample became turbid. With increasing shear rate, the value of G' increased, and the opacity became much higher. It is thought that the defects in the smectic structure are formed with applying shear and caused the light scattering. The heterogeneous structure with defects is responsible for the elastic behaviour.
At higher shear rate, the denser defective structure was obtained. For each shear rate, there was the intrinsic equilibrium state containing corresponding quantities of defects. The shear induced structure was affected only by the external stimulation.