The Viscosity of Mesophase Blends: The Cholesteryl Acetate-Myristate Pair

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Abstract
This report presents viscosity measurements on blends of cholesteryl acetate and myristate. Viscosities were measured as a function of composition, shear and temperatures over ranges corresponding to the isotropic liquid, and the cholesteric and smectic mesophases. The myristate ester was chosen as the principal constituent because its multiple phase transitions have been previously shown to be reproducible. The acetate was chosen for the blends because several workers have presented viscosity data on the neat ester. The measurements were made using a Weissenberg Rheogoniometer. The shear rates in this cone-and-plate viscometer are homogeneous and variable. The results show large breaks in viscosity behavior at the independently-measured thermodynamic transitions between the crystal, smectic, cholesteric, and isotropic states. Viscosities for the isotropic phase are Newtonian throughout. The viscosities for both the cholesteric and smectic mesophases are prominently non-Newtonian with a sharp transition between the two. A pronounced viscosity maximum is observed near the cholesteric-isotropic transition which depends on shear rate, time of shearing, and temperature programming derection. Results give sensitive transition data from which a phase diagram - including textures - may be defined since transformations are in agreement with thermal analyses indicating no measurable variation of transitions with shear and intensity.

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