Structure and dynamics of liquid crystalline droplets suspended in polymer liquids

摘要

Abstract: Small angle light scattering (SALS) and optical microscopy have been used to study micron- sized liquid crystalline droplets of 4'-n-octyl-4-cyanobiphenyl (8CB) suspended in a poly(vinyl alcohol) aqueous solution. Elliptical SALS patterns in the presence of an orienting slow flow indicate that the droplets are nonspherical in shape in the smectic and nematic regimes, but become spherical at temperatures above the nematic/isotropic (N/I) transition temperature. Upon cessation of flow, the elliptical patterns relax towards isotropy on time scales comparable to the rotation diffusion coefficient of the droplets. Using direct optical microscopy, droplets of 8CB are observed to be biconcave disc-shaped, similar to mammalian red blood cells. Reversible transitions in the drops from biconcave discs to spherical shapes across the N/I transition are seen, indicating that the nonspherical shape is due to liquid crystalline ordering. It appears that the biconcave shape provides a minimum in the free energy of curvature, balancing strong liquid crystal interactions at the interface and surface tension.!14