Screw Disclinations in Nematic Samples with Cylindrical Symmetry

Abstract

In order to verify experimentally some recent calculations on screw disclination lines in nematics we have observed with a polarizing microscope, in a meridian section, nematic filled capillary tubes with homeotropic boundary conditions, with or without inserted fibers. In the simple case with no fiber we observe non-singular S = + 1 lines and the point singularities associated with them. The lines of force of the directors are visualized by the flickering of the fluctuations of the molecules and correspond well to the shape predicted theoretically. When a glass fiber (which also imposes a perpendicular orientation on the nematic) is inserted along the cylinder axis, the Frank planar solution is stable above a critical ratio r₀/R of the fiber radius to the capillary radius. This instability appears experimentally by slightly displacing the tube. With two fibers, S = − 1 lines are created which appear to have no singular points.