The Orientational Order in Cholesteric Liquid Crystals

Abstract

The investigation of the orientational order in the mesophase of steroidal cholesterogens has been all but neglected by experimentalists, possibly because of the lack of an appropriate technique. However electron resonance spectroscopy can be used to determine the order parameter of a spin probe dissolved in a cholesteric mesophase. In addition the structure of the spin probe may be made to resemble that of the cholesteric solvent. Here this technique is employed to determine the orientational order for cholesteryl and cholestanyl benzoate, as a function of temperature. The results of these experiments yield order parameters which are comparable, or slightly smaller, than those typically observed for nematics. A comparison of these values with mean field theories suggests that the low order parameters of steroidal cholesterogens stems from deviation of the constituent molecules from cylindrical symmetry.