CURVATURE DRIVEN RELAXATION OF DISCLINATION LOOPS IN LIQUID-CRYSTALS

Relaxation of disclination loops created during shear flow of a low mo lar mass and a polymer liquid crystal were monitored using a special s hear stage with a videomicroscope. Loops in the polymer system general ly displayed initially highly distorted contours. In the small molecul e liquid crystal, the loop contours consistently exhibited very simple , generally convex shapes. In the polymer system, the complex line sha pe reflects the many prior loop-loop coalescence events due to the gre ater density of loops than in the small molecule system. Sequential im ages of loops were analysed to determine the velocity of the disclinat ion loops as a function of the local curvature. Observations and simul ations indicate that local disclination line curvature is a driving fo rce in loop evolution. The reduction of regions of high loop curvature is inherently slower in the polymer liquid crystal due to the higher viscosity. In addition, the motion of the disclination contour at very high values of curvature in the polymer liquid crystal is slowed due to the presence of lower molecular weight components at the defect cor e which themselves must diffuse along with the line defect. (C) 1998 E lsevier Science Ltd. All rights reserved.