On the occurrence of point and ring defects in the nematic-nematic coexistence range of a binary mixture of rod-like and disc-like mesogens

Abstract

We report some observations on the director configurations in the coexistence range of two nematic phases, NR and ND in a binary mixture of rod-like and disc- like nematogens. The director alignment is continuous across the boundary of the NR and ND phases. Point defects of strength + 1 in NR droplets in an otherwise continuous ND medium are found to be annulled by singular ring disclinations of strength - 1/2 Further, the NR drops which orient homeotropically at the glass plates have a point defect of strength + 1 only if their size is less than about 7 b.mum. Larger drops have ring disclinations of strength + 1/2 instead of + 1 point defects. This changeover can be understood on the basis of simple energy considerations.