Defects columnar phases

Fig. 9 (a) Sketch of the structure of the hexagonal columnar phase of DNA, showing parallel molecules hexagonally packed in the plane perpendicular to their axis, a and 4 are the lattice parameters, (b) COL developable domains observed in polarized microscopy, w indicates defect walls between differently oriented domains, while 7t stands for point defect around which DNA molecules continuously bend (size bar is 10 pm). Adapted with permission from [27]... 

Fig. 49 The homeotropic and rectilinear defect textures of the hexagonal columnar phase of supermolecule 43 (xlOO)...

Because of the conformation change and defect formation during the photopolymerization process, long coherence length of the columns in the columnar phase was difficult to maintain. Therefore, the excellent carrier transport characteristics in the columnar phases of monomeric triphenylene derivatives could not be retained in the polymerized films. 

The molecules are linked together by hydrogen bonds, and form some kind of cross-linked polymers. If the major part of the molecules constitute quasi infinite simple wires, the nodes correspond to a small number of molecules which are bound to three different neighbours. A precise study performed by X-ray diffraction and dilatometry has demonstrated that the hexagonal columnar phase can be described as an array of columns containing defects which evolve as a function of temperature [112]. 

Recently Ribeiro et al. [65] reported on the synthesis and characterization of a variety of tolanes that had optically active sulfinate groups. Some of these compounds, see 23, were found to possess a phase that exhibited oily-streak textures typical of chiral nematic phases and also defect pattern associated with columnar phases (the earlier photomicrograph Plate 6 for 14P1M7 is similar). 

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. 

No thermotropic columnar phase with a helical lattice distortion of either of the two above types has yet been reported, but concentrated solutions of DNA and poly-y-benzyl-L-glutamate show undulations and defects that indicate that such helical defect structures exist in these lyotropic systems (see section 11.5). 

US with a great benefit for device applications requiring large-areas. For the discotic columnar phases, there are few reports of the effect of structural defects on charge carrier transport. Unlike the smectic mesophases, where two dimensional transport takes place, it is likely that structural defects in a column may affect the carrier transport properties seriously, because a carrier has to pass along a column without detouring to adjacent columns. From this point of view, relatively low mobility in the columnar ordered phase of triphenylene derivatives, where the intermolecular distance is as small as 3.5 A, may be explained by the structural defects or disorder of molecular alignment in the columns as described above. 

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