Brillouin Scattering in the Isotropic Phase of Nematic Liquid Crystals under High Pressure

Abstract

Brillouin scattering in the isotropic phase of the liquid crystals (MBBA and EBBA) was investigated under high pressure up to 3.3×10³ kg/cm². The pressure variations of the sound velocities were recorded. It was found that the sound velocities did not change linearly against pressure. This effect is due to the pressure dependences of density and adiabatic compressibility. No pretransitional effect in sound velocity in the neighborhood of the nematic-isotropic transition point has been found, suggesting that the hypersonic sound wave does not couple to the molecular fluctuation even under high pressure. The adiabatic compressibilities and the molar sound velocities were calculated, and the molecular packing in the isotropic phase is discussed.