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 Q_αβ, proportional to the anisotropic part of a tensor property such as the magnetic susceptibility; (2) the free energy may be expanded in powers of Q_αβ 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 T_c. We also investigate the dynamics of fluctuations of Q_αβ, 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.