Fig. 4

Two-dimensional web of 1/2-strength twist disclinations induced by the surface orientational pattern. a Entire top view of the LC layer between partly overlapped square patterns shown in Fig. 1a (surrounded by broken red and white lines) observed between crossed polarizers. b Magnified view of a at the lower corner of the central region. c, d, Magnified polarized micrographs of a showing the square web of disclinations. The color contrast manifests the local twist and birefringence. The lattice spacing of the disclination web is 53 μm, commensurate with the periodicity of surface alignment. Disclination lines that were initially present in the central region were quickly annihilated, leaving a single loop of diagonal line surrounding the area. In the lower segment, the stripe patterns from the bottom and top substrates are horizontally parallel where the disclination lines are of the same handedness, assuring their stability. All the web structure is indefinitely stable, once the central region becomes disclination-free. Around the intersection c, d, the twist angle is 0, π, 0, and −π counter clockwise from the first quadrant. On the diagonal connecting the left bottom intersection and the right top one, the twist angle is 0, but the optic axis is continuously winding in-plane as manifested by the periodic change of contrast. With the birefringence of ZLI-2293 being Δn ~ 0.13, the interference color gives the estimate of the cell thickness to be ca. 10 μm