Disclinations columnar phases

Fig. 6.4.4. Disclinations in the columnar phase (a) and (b) —n/i and ff/3 longitudinal wedge disclinations about the sixfold axis L (c) and (d) n transverse wedge disclinations about the binary axes and 0 respectively (e) -n transverse wedge disclination leading to the formation of walls (/) two n disclinations at right angles to each other, one about 7 and the other about 0. (Bouligand. ")...

The symmetry of the columnar phase also permits the occurrence of twist disclinations in the hexagonal lattice and of hybrids consisting of a twist disclination in the hexagonal lattice and a wedge disclination in the director field. According to Bouligand these defects are not likely to exist. 

The identification of hexagonal columnar phases is relatively straight-forward. The defect textures seen in the microscope at 100 x magnification show fan-like domains, however, they lack elliptical and hyperbolic disclinations that are present for lamellar phases, see Fig. 19. 

Another type of interpretation of the textures was proposed by Nas-tishin et al., who suggested that the By phase is a smectic and columnar phase at the same time. The geometry of the helical filaments (ribbons) is that one of the central region of a screw disclination with a giant Burgers vector split into two disclination lines of strength V2/ which boimd the ribbon. 

According to Fig. 3, classical thermotropic smectic phases of amphotropic liquid crystals are (SmA ), colunmar hexagonal (Col ), bicontinuous cubic (Cub, i), or discontinuous cubic (Cubjis) [169]. All these meso-phases include a disclination surface between the hydrophilic and the lipophilic parts of the unordered molecules. This surface can be uncurved (SmA), curved in one direction (columnar), curved in two directions with the same sign (discontinuous cubic), or curved in two directions with opposite sign (bicontinuous cubic). 

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