Normal Stress Effects in Cholesteric Mesophases

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Abstract
Normal forces have been found in rheological studies on cholesteryl chloride‐cholesteryl oleyl carbonate liquid crystal mixtures over the composition range 0–27 wt.% cholesteryl chloride. These normal forces appear to be associated with the homeotropic texture and are evident in the transition region for the shear induced focal conic to homeotropic transition. The Kotaka model for normal stresses arising from hydrodynamic interactions of rotating rods has been applied. The results are consistent with a model of the homeotropic texture of the cholesteric mesophase comprised of rodlike helical arrays of molecules rotating in an applied shear field. The calculated rod lengths are less than the characteristic pitch of the material.