DISCLINATION CORE STRUCTURE IN RIGID AND SEMIFLEXIBLE MAIN-CHAIN POLYMER NEMATIC LIQUID-CRYSTALS

In order to ascertain the near-core structure of +/-1/2 wedge disclinations, the apparent splay and bend elastic anisotropy, epsilon(app), is measured as a function of radial distance from the singularity. Epsilon(app) = [(k11)a - (k33)a]/[(k11)a + (k33)a]. Both a rigid and a semiflexible main-chain liquid crystal polyester are studied. Results demonstrate a special structure of the core at radii less than about several molecular lengths. The rigid material splays significantly more; at a distance of 0.1 mum, epsilon(app) is approximately -0.4, yet the asymptotic value, epsilon (at a distance of 1 mum), is approximately 0. In contrast, the semiflexible material bends more; epsilon(app) (0.1 mum) approximately 0.1 and epsilon approximately -0.15. These results can be understood in terms of the molecular lengths and relative rigidities of these liquid crystalline materials. The presence of hairpins in the flexible-chain polymer is suggested.