Temperature Dependence and Rheological Behavior of the Shear-Induced Grandjean to Focal Conic Transition in the Cholesteric Mesophase
This report is a study of the shear induced Grandjean to dynamic focal conic transition by rheological and thermal measurements. Previous structural postulations of the sheared choles-teric mesophases are consistent with the observed data. For a room temperature cholesteric mixture of Cholesteryl Oleyl Carbonate (COC) and Cholesteryl Chloride (CCl) (23% by wt. CCl) activation energies for viscous flow are identical for the Grandjean and dynamic focal conic textures and equal to 15 Kcal/mole. Extrapolation of the dynamic focal conic viscosity region into the isotropic region is continuous. Transient rheological phenomena in the transition region are temperature dependent and are shown to be associated with non-equilibrium tilting of the cholesteric helices and breakdown of the normal Grandjean structure. The activation energy for the shear induced conversion of Grandjean to dynamic focal conic texture is 25 Kcal/mole.
KeywordsShear Rate Liquid Crystal Critical Shear Rate Surface Constraint Torque Response
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