Brillouin Scattering in the Isotropic Phase of MBBA

Abstract

We report here the results of our study of Brillouin scattering in the isotropic phase of the nematic liquid crystal para-methoxybenzylidene p-n-butylaniline (MBBA). In the nematic phase the anisotropic molecules of this material exhibit long range orientational order with their long axes tending to align parallel, while in the isotropic phase the molecular axes are randomly oriented. Although the isotropic phase shows no net order, the mean squared amplitude of fluctuations in the order becomes large near the nematic-isotropic transition¹. In this paper we predict the effect of these fluctuations on the spectrum of Brillouin scattered light in the isotropic phase of a nematic liquid crystal. We show the spectrum obtained for Brillouin scattering in the isotropic phase of MBBA, give values of the hypersonic velocity and attenuation measured in the temperature region just above the nematic-isotropic phase transition, and compare these values with ultrasonic data.