Disclinations and Their Interactions in Thin Films of Side-Chain Liquid Crystalline Polymers

Abstract

Two-dimensional disclinations formed in thin films of a side-chain liquid crystalline polymer are investigated using transmission electron microscopy (TEM). The detailed director patterns are revealed through nanoscale stripes, which are parallel to the molecular director. One hyperbolic pattern of a negative disclination with a charge s = −1 and three patterns involving radial, circular, and spiral director fields of a positive disclination with s = +1 are observed. Positive disclination cores are found to exhibit circular dark centers while the s = −1 is shown to have a bright central core. The difference in TEM contrast is attributed to the nature of the packing within the core. From the director texture around a disclination it is possible to determine the elastic anisotropy, which is not higher than 0.1. Observing the time evolution of the disclination density, it is found that the average number of defects in the plane scales with time as N ∝ t-3/4. It is found that both translation and rotation motions occur for a pair of (+1, −1) disclinations, leading to the formation of a certain special configuration shortly before the pair annihilation. In some cases, not the pairs but the linear clusters of three-disclination dominate the interaction. Theoretical analysis is presented to explain this new phenomenon. In addition, director inversion walls are observed to form during the late stage of disclination annihilation. It is found that inversion walls always separate a pair of (+1, +1) disclinations.