Photo-alignment control of topological defects in nematic liquid-crystal cells

摘要

We report the experiments aimed at controlling the position of linear topological defect (disclination) in a so-called theta-cell filled with a nematic liquid crystal sandwiched between circularly rubbed polyimide (Kapton) layer and photo-aligning PVCN material oriented unidirectionally. To satisfy surface-alignment conditions, the director within this cell experiences a twist. The topological defect appears in a plane where the twist angle of the director becomes indeterminate (+/- 90 degrees). In an achiral liquid crystal, orientation of the disclination coincides with the alignment occurring on the unidirectionally oriented substrate. The idea of this work is to control the alignment direction on the substrate by a polarized ultraviolet light. Photo-induced director reorientation on the substrate changes the twist angle in the bulk and so varies the azimuthal angle of the disclination. We monitor reorientation of the disclination as a function of light-polarization angle and irradiation dose.