Depolarized Rayleigh scattering in liquids: The density and temperature dependence of the orientational pair correlations in liquids composed of anisometric molecules

Abstract

Structural analogs of the nematic liquid crystal p-methoxybenzylidene-n-butylaniline (MBBA) have been synthesized and the static orientational pair correlations (OPC) have been examined by light scattering. From the intensity of the depolarized Rayleigh scattered light, the OPC's have been determined in the neat isotropic liquid and in solution with carbon tetrachloride as a function of concentration and temperature for two of these molecules, p -methylbenzylidene-n -butylaniline (MBA) and p -ethylbenzylidene-n -butylaniline (EBA). The density dependence of the OPC's of these molecules and MBBA are analyzed in terms of the structure and polarity of the scattering molecules. The OPC's of the isotropic liquid trans -cinnamaldehyde have also been determined. We find that the molecular size and shape (repulsive forces) largely determine the extent of orientational order in these liquids. The attractive intermolecular forces affect the orientational order (static OPC) by increasing the density (at a given temperature). Several conclusions relating the static OPC and the onset of the nematic liquid crystalline phase are also discussed.