Thin Nematic Films: Laboratory of Physics for Topological Defects

In this pedagogical presentation we demonstrate basic physics of topological defects in orientational ordering. We limit to two dimensional (2D) films. Different defect structures and pairs defect-antidefect are visualized in the applet presentation, which shows also the corresponding interference textures simulating typical polarizing microscopy experiment. The conservation of topological defect is shown on the case of 2D films on curved surfaces. In different geometrical shapes with the same Euler characteristics we demonstrate equilibrium (or at least relatively stable) nematic structures possessing 2 to 8 defects pairs with the winding number vertical bar M vertical bar = 1/2, where the sum of all defects corresponds to M-tot = 2.