Analysis of Shear Flow Effects on Liquid Crystalline Textures

Abstract

A model for the shape and motion of disclination loops observed in thermotropic small molar mass and polymeric nematic liquid crystals in the presence of steady rectilinear shear and oscillatory rectilinear shear flow is presented. In steady rectilinear simple shear, disclination loops elongate and tumble, before retracting to points, in a time that increases with increasing shear rate. In oscillatory shear the loops' shape oscillate with decaying amplitudes between ellipses and circles; the retraction time decreases with increasing frequency. As the driving frequency increases the retraction time decreases. A model for loop population dynamics accounting for the continuous loop creation by surface sources, and loop motion and deformation due to steady rectilinear simple shear predicts that the total number of loops increases with increasing shear rates. The above predictions are in qualitative agreement with experimental results.^5,6 Shear thickening and shear thinning are predicted according to the magnitude of the shear rate and the sensitivity of the initial loop orientation to the strength of the flow.

Key Words:

• disclination loops
• textures
• surface nucleation
• shear flow effects