Hexagonal columnar phase

McMillan s model [71] for transitions to and from tlie SmA phase (section C2.2.3.2) has been extended to columnar liquid crystal phases fonned by discotic molecules [36, 103]. An order parameter tliat couples translational order to orientational order is again added into a modified Maier-Saupe tlieory, tliat provides tlie orientational order parameter. The coupling order parameter allows for tlie two-dimensional symmetry of tlie columnar phase. This tlieory is able to account for stable isotropic, discotic nematic and hexagonal columnar phases. 

These compounds show a nematic and smectic C phase for relatively short chain lengths (n 7-10) and a hexagonal (columnar) phase for longer chains. 

Fig. 3. An idealized representation of the supramolecular cylinder self-assembled from a single chain of the dendrimer derived from monomer 9 (R=OC12H25, n=3) in the hexagonal columnar phase, assuming one single backbone per cylinder, drawn to proportion with existing experimental data a tilted side view b top view. Reproduced with permission from references 5 a...

Nucleosome-nucleosome interaction potentials can be calibrated by comparison with the characteristics of liquid crystals of mononucleosomes at high concentrations. Under suitable conditions, nucleosome core particles form a hexagonal-columnar phase with a distance of 11.55 1 nm between the columns and a mean distance of 7.16 0.65 nm between the particles in one column [44,46]. These distances may be assumed to correspond to the positions of the minima of an attractive internucleosomal potential. The depth of the interaction potential (i.e., the binding energy per nucleosome) was estimated in the stretching experiments of Cui and Bustamante [66] to 2.6-3.4 kT. A slightly lower potential minimum of 1.25 kT is obtained by a comparison of the stability of the nucleosome liquid crystal phase with simulations [50]. 

For some systems, at high concentration, inverse phases are observed. That is, one may generate an inverse hexagonal columnar phase (columns of water encapsulated by amphiphiles), or an inverse micellar phase (a bulk LC sample with spherical water cavities). 

Bicontinuous cubic phase Lamellar phase Bicontinuous cubic phase Reverse hexagonal columnar phase Inverse cubic phase (inverse micellar phase)... 

Recently, polyphilic compounds have been reported, where an Rp-chain and a carbosilane chain were attached at opposite sides of a terphenyl or oligo (p-phenylene ethinylene) core [42], Compound 188 with the longest oligo (p-phenylene ethinylene) core shows two hexagonal columnar phases separated by a thermoreversible continuous (second order) phase transition with critical behavior upon approaching the transition temperature. Based on XRD data it was... 

The columnar phases of oligobenzoate Hekates are most probably formed from -shaped conformers which pack disordered in hexagonal columnar phases and for symmetric mesogens they can tilt and aggregate in highly ordered helical arrangements to form the 3D columnar structures (see Fig. 10a, b). Indications... 

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]... 

Kumar et al. nevertheless succeeded in creating stable suspensions of hexanethiol-capped gold nanoparticles (1.6 nm core diameter) and gold nanoparticles capped with a 10CB thiol (similar to nanoparticle 3 in Fig. 5) in a lyotropic hexagonal columnar phase (HI phase formed by a 42 58 w/w Triton X-100/water system) as well as an inverse hexagonal columnar phase (H2 phase formed by AOT). Both types of nanoparticles were shown to stabilize the HI phase... 

Fig. 20 Schematic models of the gold nanoparticle strings (a) rhombohedral phase of 14 and (b) hexagonal columnar phase of 13. Gold nanoparticles are in yellow, mesogens in green [542]. (Copyright Wiley-VCH Verlag GmbH Co. KGaA, reproduced with permission)...

Kozhevnikov, Bruce, and coworkers described an LC N,C,N-coordinated plati-num(II) derivative 4 showing mechanochromic luminescence (Fig. 4) [31]. Compound 4 shows a hexagonal columnar phase up to 145 °C and another hexagonal columnar phase up to 220 °C. A pure film of compound 4 shows a red excimer-like emission at room temperature. Interestingly, the photoluminescent color of compound 4 changes from red to yellow by annealing at 110 °C and the yellow photoluminescence is preserved after cooling to room temperature. The red... 

Knupp, C., Luther, P. K., Morris, E. P., Knight, D. P., and Squire, J. M. (1999). Partially systematic molecular packing in the hexagonal columnar phase of dogfish egg case collagen. / Struct. Biol. 126, 121-130. 

Colh, Colho hexagonal columnar phase p6mm symmetry)... 

Figure 13. Schematic representation of supramolecular structures of rod-coil molecules 10. (a) Smectic A, (b) bicontinuous cubic, and (c) hexagonal columnar phases. (Reprinted with permission from ref 64. Copyright 1998 American Chemical Society).

Columnar phases could also be obtained by reacting disk-shaped molecules such as crown ethers with lanthanide salts. BiinzU and coworkers reported, for example, the preparation of thermotropic hexagonal columnar phases from nonmesogenic crown ethers and several different ions of the lanthanide family [76], An additional property of these compounds is a metal-centered emission, in the case of the liquid-crystalline phases containing Eu and Tb, making them attractive for the design of luminescent liquid-crystalline materials [76],... 

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