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, N_R and N_D in a binary mixture of rod-like and disc- like nematogens. The director alignment is continuous across the boundary of the N_R and N_D phases. Point defects of strength + 1 in N_R droplets in an otherwise continuous N_D medium are found to be annulled by singular ring disclinations of strength - 1/2 Further, the N_R drops which orient homeotropically at the glass plates have a point defect of strength + 1 only if their size is less than about 7 μm. 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.

Key Words:

• point defects
• ring defects
• nematic-nematic coexistence