Light scattering in the isotropic phase of highly chiral liquid crystals

Abstract

Light-scattering measurements using circularly polarized light in a backscattering geometry are employed to measure the amplitude of fluctuations in two of the five structural modes present in the isotropic phase of chiral liquid crystals. From these measurements, the second-order transition temperatures for all five modes are then calculated. In order to investigate the effect of chirality on the fluctuations, the experiments are performed in various mixtures of the chiral liquid crystal 4’ ’-(2-methylbutylphenyl)-4’-(2-methylbutyl)-4-biphenylcarboxylate (CE2) and the nonchiral liquid crystal 4-n-pentylbenzenethio-4’-n-heptyloxybenzoate(7¯S5). The results show that fluctuations in the five modes are independent in low-chirality mixtures, and, as predicted by theory, the second-order transition temperatures grow farther apart as the chirality increases. In highly chiral mixtures, fluctuations in the mode with the highest second-order transition temperature deviate from the normal temperature dependence, resulting in a lower second-order transition temperature for this mode. The probable explanation for this is that fluctuations in the structural modes are coupled in high-chirality systems, but at present no theoretical calculations exist.