Textures columnar phases

Compound 114d possesses significantly lower transition temperatures (Scheme 60) due to the branched side chains [126]. A columnar phase is present even below room temperature. At 14 °C, anew chiral columnar phase was observed while above 111 °C, an achiral columnar rectangular phase was observed. The spiral-pattern texture of 114d in the chiral Col mesophase is shown in Fig. 17. 

Fig. 9 Textures of the columnar phases of compound 34b. Pseudo-focal conic texture at 92 °C of the Colhd phase (bottom) and at 74 °C in the body-centred orthorhombic columnar phase (top). In order to increase the dynamic range of the photographs various photos with different exposure times have been superimposed. The black Maltese cross is perfectly dark in the centre for the Colhd- In the low temperature phase undulation of the columns produces birefringence in the dark branches...

Figure 13.21 Contact region at 78 °C showing the phase sequence smectic-A (fan texture), M (unidentified mesophase), hexagonal channelled layer phase (ChLhex), square columnar phases p4gm and p4mm (from left to right) upon increasing concentration of 13.18 (reproduced by permission of The Royal Society of Chemistry). See plate section for colour version of this image.

Compound 43 was found to exhibit a chiral nematic phase (see the texture in Fig. 48), hexagonal disordered columnar (see Fig. 49) and rectangular disordered columnar phases, in the sequence g 5.4 Col d 30 Col 102.3 N 107.7 °C Iso Liq [94]. Thus the increase in the number density of the meso-gens bound to the central scaffold transforms the situation from the octamers 41 and 42, which exhibit calamitic phases, to one where the hexadecamer 43 exhibits columnar phases. However, the formation of columnar phases when the dendrimer possesses rod-like mesogenic groups is not easy to vi-... 

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

Doubly hydrogen-bonded supramolecular polymers 35 and 36 consisting of carboxylic acid and diaminopyridine moieties exhibit monotropic liquid-crystalline behavior [63a, 83]. A texture of dendritic growth characteristic of columnar phases is seen for the complex [63a]. 

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). 

Lyotropic cellulosics mostly exhibit chiral nematic phases, although columnar phases have also been observed. The molecules in the thermotropic state also form chiral nematic order, but it is sometimes possible to align them in such a way that a helicoidal structure of a chiral nematic is excluded. Upon relaxation they show banded textures. Overviews on lyotropic LC cellulosics are... 

The widest columnar mesophase temperature ranges were obtained for the bis-[l,3-di-(substi-tuted-phenyl)-/3-diketonate] metal complexes bearing ten and twelve chains ((55) R = H or OC H2 +i). The ten-chain copper, palladium, and oxovanadium(IV) complexes ((55) M = Cu, Pd, VO R = H, = 6, 8, 10, 12, 14) were all mesomorphic and the enantiotropic mesophases were identified by optical texture and variable-temperature X-ray diffraction as columnar phases (Table 34). The copper and palladium complexes displayed a Coh phase for short chain length ( = 6, 8 for M = Cu = 6, 8, 10 for M = Pd), which transformed to a Coin phase as the chain length was increased. Surprisingly, no direct Cok-to-Colh phase transition was observed within the same compound, but weakly first-order Cok-to-Cok and Colh-to-Colh phase transitions were found for compounds with intermediate chain lengths. In contrast, the vanadyl complexes exhibited only one Coh mesophase. Infrared studies indicated that the VO complexes possessed a linear V=0—V=0 linear polymeric chain structure in the crystal phase, while no... 

Liquid crystalline triphenylene hexacarboxyUc esters 15 have been recently synthesized and the columnar phase has been observed to align homeotropically on different substrate surfaces [82]. The alignment behavior has been studied by polarizing optical microscopy and X-ray diffraction techniques. POM shows a dark view whereas optical microscopy image displayed a dendritic texture typical of columnar hexagonal assembly. The hexagonal columnar phase displays... 

Fig. 9.3. (a) Texture of the columnar phase, (b) Columnar phase composed of the disk-shaped molecules in Fig 9.2. Note the irregular positioning of molecules along a column... 

Between crossed polarizers, the phase transition into a columnar phase is often accompanied by a dendritic growth of the texture. If the director is oriented perpendicular to the viewing direction, pseudo-focal conic fan-shaped textures can be observed. If the viewing direction is parallel to the director, a platelet texture is formed. 

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. 

Rg. 19 Texture of the columnar phase of a synthetic diether-type gtycolipid under crossed polars (x 100). 

Apart from the triphenylene mentioned in Section 11.2, one other case has been reported where a chiral columnar phase structure manifests itself in an asymmetric texture 2,3,9,10,16,17,23,24-octakis-(5-3,7-dimethyloctyloxy)-phthalocyanine exhibits two columnar phases above room temperature [8], [14]. The one at the higher temperature has a rectangular column lattice, the other a hexagonal one. When cooled quickly from the isotropic liquid, left-handed spirals appear in the flower-like texture of the highly ordered room temperature phase (Figure 11.8). X-ray and circular dichroism measurements indicate a helical superstructure with a pitch of 55 A (a 16 molecules). It seems very probable that in this case the molecules are weakly tilted and that the tilt direction spirals around the column axis, especially because the phase at higher temperatures is rectangular and therefore most probably tilted as well. 

The Bj textures show characteristic helical filamentary growth in cooling from isotropic melt. i- 2 However they denote at least two distinct phases. X-ray measurements clarified that the original By materials, which form freestanding strands, - just like columnar liquid crystals of disc-shape molecules (see Chapter 2), indeed have a columnar phase (hereafter we will label them as Bj j). Other By-type materials (we call them Byu) were foimd to have modulated layer structures. We note that the By and B2 type banana-smectics also form strands of fibers. ... 

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