Hexagonal columnar mesophases

Kim, S.J., Kang, S.H., Park, K.-M., Kim, H Zin, W.-C., Choi, M.-G. and Kim, K. (1998) Trinuclear Gold(l) Pyrazolate Complexes Exhibiting Hexagonal Columnar Mesophases with Only Three Side Chains. Chemistry of Materials, 10, 1889-1893. 

Trzaska and co-workers showed a similar propeller mechanism for the formation of helical columns from disclike metallomesogens (29-31).34 These metallomesogens also have C3 symmetry and 30 and 31 are provided with chiral side chains. In the hexagonal columnar mesophase these chiral side chains induce a Cotton effect in the chromophore of the helically arranged core. Heating the mesophase to the isotropic liquid results in the disappearance of the Cotton effect because of the loss of helical order. This effect illustrates the need for the molecules to be positionally ordered in order for the side-chain chirality to be transferred to the supramolecular column. 

Figure 16.10 Conformational changes of polypropylene imine) dendrimers in LC materials from spherical to (a) cylindrical, in hexagonal columnar mesophase [130], and (b) ellipsoid, in smectic A mesophase [132]...

The X-ray diffraction patterns show that the materials obtained from the various configurational isomers of tartaric acid have different architectures. Both are hexagonal columnar mesophases, but, whereas the data for (LP2, LU2) are consistent with columns formed by three polymeric strands having a triple helix superstructure (Figure 41), those for the (MP2, MU2) mixture fit a model built on three strands in a zig-zag conformation. The LD mixture has another arrangement again. 

However, all the dendrimers prepared showed only a hexagonal columnar mesophase, even those bearing the largest mesogenic units containing... 

The complex with [Li+]/[PO] = 0.10 exhibits a crystalline melting transition followed by a smectic A mesophase. By increasing the salt concentration as in the case of complexes with [Li+]/[PO] = 0.15 0.30, the smectic A phase is suppressed instead, they exhibit a hexagonal columnar mesophase as evidenced by X-ray scattering. The induction of ordered structure in the melt state of the rod—coil molecule by complexation is most probably due to enhanced microphase separation between hydrophobic blocks and polypropylene oxide) block caused by transformation from a dipolar medium to an ionic medium in polypropylene oxide) coil. 

Noguchi T, Kishikawa K, Kohmoto S (2008) Volume effect of alkyl chains on organization of ionic self-assemblies toward hexagonal columnar mesophases. BuU Chem Soc Jpn 81 778-783... 

Figure 2.10 Schematic representation of a hexagonal columnar mesophase (Colh)...

The rod-coil approach as a means to manipulate supramolecular structure as a function of rod volume fraction was reported to be extended to main chain multiblock copolymer systems, which generate bicontinuous cubic and hexagonal columnar mesophases depending on the rod-to-coil volume fraction [95,96]. For example, rod-coil multiblock copolymer (28) based on short length of coil (rod volume fraction, /ro(j = 0.38) exhibits a bicontinuous cubic mesophase, while copolymer (29) based on higher coil volume fraction (/i-od = 0.29) shows a hexagonal columnar mesophase. A notable feature... 

Interestingly, the 3 1 complex with the less symmetrical 3,4-substituted benzoic acid shows a more stable mesophase (K 79 M 244 I) than the derivative formed from the 3,4,5 substituted benzoic acid (K 63 M 214 I). A related system has also been reported which uses a benzotri(imidazole) (23) as the trifunctional core unit (Fig. 12b) along with benzoic acid derivatives (24). This 1 3 complex exhibits a hexagonal columnar mesophase between 23 °C and 75 °C. The acrylate moieties on the alkoxyl chains could be photopoly-merized to covalently fix the LC phase. Removal of the supramolecularly bound benzotri(imidazole) core yields a nanoporous polymer film containing hexagonally-ordered channels-opening the door to the potential application of these materials in such areas as separation, nano-composites, and catalysis. 

Silver thiolate compounds (AgSR) adopt a bilayer structure in the crystalline state [168] with a central slab of 3-SR and trigonal planar Ag. On melting, these compounds form lamellar, cubic, micellar and hexagonal columnar mesophases, depending on the length of R [169]. 

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