Observations on a Nematic Liquid Crystal with an Oblique Orientation of the Director at the Nematic-Isotropic Interface

Abstract

We report some observations on the nematic isotropic (NI) interface of 4'-heptyl-4-cyanobiphenyl (7CB). 4-cyanophenyl-trans-4'-n-heptylcyclohexane (PCH-7) and a mixture of PCH-5 with a nonmesomorphic compound. In the mixture the director makes a tilt angle ∼45° at the NI interface leading to a new structure of nematic drops floating in the isotropic phase. The structure is characterised by two point defecis at the poles and a line deflect at the equator. When thin films of this mixture and of 7CB are spread on a slide treated for homeotropic alignment, the NI interface develops a regular network of point defects of strength ± 1 arranged in a square lattice. It is associated with conical distortions in the surface profile. which are generated to lower the elastic energy of the sample as was predicted by de Gennes. The conical distortions can be directly seen at the NI interface of a PCH-7 sample mounted in a hole in a coverslip.