Point Disclinations at a Nematic-lsotropic Liquid Interface

Abstract The optical properties of a thin film of liquid crystal, with one of its surfaces bounded by the isotropic liquid of the same compound, reveal the existence of point defects in the liquid crystal. Particular sample geometries are examined in which the detailed structure of the optical patterns seen with polarized light can be analyzed to develop a qualitative picture of the structure of the liquid crystal layer near the defects. Changes in the optical pattern induced by an electric field are also analyzed. The observations indicate that the defects are point disclinations at the sirface of the liquid crystal, of the kind recently described by deGennes, rather than line disclinntions emerging from the liquid crystal.