Twist disclination loops in a bent-core nematic liquid crystal

Abstract

We report on the generation and stability of half-strength twist disclination loops separating planar and π-twisted regions in a bent-core nematic liquid crystal with planar anchoring. Loops L(P) and L(T) surrounding planar and π-twisted domains, respectively, are both generated during relaxation from the quasi-homeotropic splay-Freedericksz state. We demonstrate that the metastable twisted state occurs as a rule in the region of lateral separation of singular loops formed via wall pincement and collapsing at different rates. The results provide the first experimental confirmation of the early theoretical prediction that, for circular loops L(P), there exists a critical radius R_c separating regimes of growth and decay. R_c varies with temperature indicating its dependence on elastic anisotropy. R, which changes quasistatically around R_c, is linear in time in the long thread regime for both L(P) and L(T). An earlier model for L(T) is extended for L(P) to fully account for the observed dynamics of both subcritical and supercritical loops, and also to extract the related viscoelastic parameter.