Short Range Order Effects in the Isotropic Phase of Nematics and Cholesterics

Abstract

We assume that (1) the local state of order in the isotropic phase is a symmetric traceless tensor Qαβ, proportional to the anisotropic part of a tensor property such as the magnetic susceptibility; (2) the free energy may be expanded in powers of Qαβ and of its gradients. This allows a unified description covering the anomalous magnetic birefringence, the intensity of light scattering, and the properties of the nematic/isotropic interface. For a cholesteric, although the optical rotation is huge in the ordered phase, we predict that it should not be anomalous just above the transition point Tc. We also investigate the dynamics of fluctuations of Qαβ, and discuss the flow birefringence, the frequency width of the Rayleigh scattering, and the attenuation of ultrasonic shear waves, in terms of 3 viscosity coefficients.