Controlling the Self-Assembly of Periodic Defect Patterns in Smectic Liquid Crystal Films with Electric Fields

Large-area periodic defect patterns are produced in smectic A liquid crystals confined between rigid plate electrodes that impose conflicting parallel and normal anchoring conditions, inducing the formation of topological defects. Highly oriented stripe patterns are created in samples thinner than 2 mu m due to self-assembly of linear defect domains with period smaller than 4 mu m, whereas hexagonal lattices of focal conic domains appear for thicker samples. The pattern type (1d/2d) and period can be controlled at the nematic-smectic phase transition by applying an electric field, which confines the defect domains to a thin surface layer with thickness comparable to the nematic coherence length. The pattern morphology persists in the smectic phase even after varying the field or switching it off. Bistable, non-equilibrium patterns are stabilized by topological constraints of the smectic phase that hinder the rearrangement of defects in response to field variations.