Disclinations and Properties of the Directorfield in Nematic and Cholesteric Liquid Crystals

Structure and properties of disclination lines and disclination points in nematic and cholesteric liquid crystals are reviewed. An equivalence between the directorfield of nematics and electrostatic or magnetostatic fields in two-dimensions is pointed out. Dislination lines can be classified in singular and non-singular lines. Disclination points correspond always to singular solutions. They are often associated with non-singular lines. Experimental observations of disclinations, of surface patterns in cholesterics, and of cholesteric textures are described. Structural features of special cholesteric “focal-conic” and “fan” texture are discussed in terms of the vectorfield defined by the twist axis.