Optical Activity and Light Scattering in Cholesteric Liquid Crystals: Theoretical and Experimental Considerations

The work deals with an electro-optical study of chiral nematic liquid crystals, S-(+)-4-(2- methybutyl) phenyl 4-decyloxybenzoate (CE6) and Cholesteryl Nonanoate (CN), a cholesteric polymer, C4745, and a 90%CE6-10% C4745 mixture through the use of optical activity and light scattering techniques. An expression for the optical activity in chiral nematic liquid crystals has been derived for zero field. This derivation represents an extension of the present theory of optical activity in chiral nematics. Dynamic light scattering studies were performed on various concentrations of CE6- CE6R. From these results, phase diagrams were constructed for the CE6-CE6R mixtures. The ransition to the blue phases becomes more continuous with increasing chirality. The light scattering data can be fitted to a single exponential over a wide temperature range. The scattered intensity increases with increasing chirality and with increasing electric field. The isotropic transition becomes more discontinuous as the electric field increases. The electric field destroys the contribution from the m = 2 modes while enhancing the contributions from the m = 0 mode.