Abstract
The viscosities of cholesteryl myristate (ChM), cholesteryl palmitate (ChP) and cholesteryl oleate (ChO) were measured with a cone-plate viscometer at various shear rates with continuous heating. After a rapid decrease near the smectic-cholesteric transition temperature, the viscosities decreased gradually in the cholesteric and isotropic phases, with a peak at the cholesteric-isotropic transition. The viscosity peak temperature agrees reasonably well with the values obtained by differential scanning calorimetry (DSC) and polarized light microscopy. From the shear rate vs. shearing stress relations at various temperatures, it was concluded that the flow in the isotropic phase was Newtonian, while the flow in the cholesteric phase was non-Newtonian. With respect to the cholestericisotropic transition temperature, the effect of alkanols on the viscosity of ChM was the same as that on the DSC curve. However, the viscosity vs. temperature curve showed a stronger transition peak than the DSC curve, in spite of the addition of alkanols. The change of ChM viscosity under stress was also followed at various temperatures ; the "static viscosity" was obtained by extrapolation of the viscosity to zero time and the "kinetic viscosity" from the steady-state value under stress. Comparison between the viscosity measured with continuous heating and the kinetic viscosity confirmed the validity of the former method, especially in the isotropic and cholesteric-isotropic transition states.
