Electric field generated solitons, disclinations and vortical flows in freely suspended nematic 8CB

摘要

We present the results of optical studies on the instabilities in a substrate-free nematic 8CB film, subject to an in-plane electric field. The initial director field involves a -1/2 strength disclination loop, separating the central pseudoisotropic zone from the splay-bend" (SB) birefrin-gent boundary. Three regimes of sample thickness are distinguishable on the basis of field-induced instabilities. Thick (～ 75 μm) films display growth of SB zones (independently of disclination movement), wall-formation, and reversible transition between walls and disclinations. Moderately thick films, a few μm in the central part, exhibit distinctive undulations at the border of advancing SB layers. Submicron thin films, with smectic-like homeotropic central plateau, show spectacular isotropic vortex-pairs at either end of this plateau. Further, the end regions of the birefringent zone exhibit both eleetro-convective flows and reorientational effects. The latter are associated with the formation of open and closed walls, and loop-wall emission. The final high field instability involves jet-like flows at the two ends of the film.