Hexagonal architecture

The thermal stability of mesoporous frameworks substantially increases with an increase in the wall thickness and pore size, which can be varied even for the same template by changing the processing conditions. Ozin et al.55 developed a way to prepare crystalline titania films with a 2D-hexagonal architecture by replacement of ethanol in the Pluronic-containing precursor solution with more hydrophobic butanol-1. The latter promotes phase separation at low surfactant-to-titania ratios, resulting in thicker pore walls, which are more compatible with the crystal growth during subsequent calcination. 

Description of the hexagonal architecture of the liver lobule and of the anastomoses of the fine bile capillaries by F. Kiernan. (s. fig. 1.18)... 

The first was the physical restriction of the jjeptide motion, more specifically its diffusion within the water cylinders, owing to the geometric constrain of hexagonal architecture. The second factor is the chemical interactions of the peptide with the polar heads of monoolein. These two effects were separated and quantified by SD-NMR analysis (SD-NMR). Rankin s model [43] was used to calculate the theoretical diffusion coefficients of desmopressin within the channels of the Hu mesophase, assuming no interactions of the peptide with GMO and TAG. Using the theoretical diffusion coefficient of the drug and the measured diffusion values, the observed decrease in diffusion coefficients of the peptide in the Hn mesophase was clarified (Fig. 12.23), defining two obstruction factors. The obstruction factors enabled quantification of the effects of both physical restriction (p) and the chemical interactions (y). 

Composites of PPV in films of the polyelectrolyte Nafion have been synthesized by electrostatically binding the dicationic monomer to the film, followed by treatment with base and thermal conversion (48). Ordered nanocomposites of PPV have been synthesized from mixtures of polymerizable lyotropic liquid crystals with PPV precursors (49). Photopolymerization of the host results in a hexagonal architecture, which can be fabricated into fibers and thin-films. A significant enhancement in photoluminescence of the composite relative to PPV was found. 

Peculiar DNA architecture was demonstrated in 25% aqueous ethanol when DNA was complexed with series of cationic detergents in the presence of poly(glutamic acid) [124]. Electron microscopy and x-ray scattering demonstrated that DNA can pack cetyltrimethylammonium bromide molecules into rodlike micelles, which form a hexagonal lattice. Interestingly, circular dichroism spectroscopy revealed that in these complexes DNA adopts left-handed conformation. 

The term star-block copolymer is used for a star architecture in which each arm is a diblock. The influence of chain topology on mechanical and morphological properties was investigated for copolymers composed of PS and PB with a constant styrene content of = 0.74 by Michler s group (Fig. 32) [101,102], While hexagonally packed cylinders of PB in a PS matrix were observed in a symmetric PS-fo-PB-fr-PS triblock copolymer, an L phase... 

The nanoreplication of functional nanostructures has also been achieved through other block copolymer-templated structures. De Boer et al. [35] applied honeycomb-structured films of rod-coil block copolymer as patterned templates to replicate hexagonally packed arrays of aluminum cups on the substrate surfaces (Fig. 10b). Nguyen et al. [237] embedded semiconducting polymers in the channels of oriented hexagonal nanoporous silica and used this nanoscale architecture to control the energy transfer for potential optoelectronic applications. 

MCM-41 is most extensively studied member of the M41S family because of its hexagonal array of unidimensional pore architecture. In addition to catalysis, MCM-41 type mesoporous materials are increasingly being explored for a variety of different applications, such as support, as sensors / carriers, surface modification etc. 

Organically modified porous silicates have been prepared under acidic conditions, by direct reaction of a mixture of phenyltriethoxysilane (PTES) and tetraethoxysilane (TEOS), and an aqueous solution of cetyltrimethylammonium bromide (CTAB). For a 1 4 molar ratio between PTES and TEOS, the hexagonal (2d, p6m) phase, but also a cubic phase analogous to the already reported SBA-1 phase (Pm3n), can be prepared. The surfactant can then be efficiently removed by calcination at 350°C, leading to phenyl-functionalized microporous silicates with two types of architecture. The influence of several parameters (PTES/TEOS ratio ethanol content) that affect the organization of the samples, will be discussed. 

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. 

Figure 9.1 Schematic representation of some of the simple network architectures structurally characterised for metal-organic polymers (a) 2D honeycomb, (b) ID ladder, (c) 3D octahedral, (d) 3D hexagonal diamondoid, (e) 2D square grid, and (f) ID zigzag chain (reprinted from Section Key Reference The American Chemical Society).

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