Blue phase structure

Kitzerow et al. in 1993 formed blue phases of polymeric liquid crystal monomers and polymerized these monomers while maintaining the blue-phase structure, leading to a solid resin of fixed blue-phase structure [22]. Such a substance, although maintaining the blue-phase structure, provided none of the dynamics of liquid crystal, since all the constituent molecules were polymerized. 

In 1993, Kitzrow et al. formed a blue phase with polymerizable crystal monomers the monomers were polymerized in the blue phase, which immobilized the molecules, thus preserving the blue phase structure in the solid resin [16], In this type of material, although the characteristics of the blue phase stmcture had been preserved, the dynamics of the liquid crystal had been lost because aU molecules had been polymerized and thus immobilized to a certain extent. 

The structures of phases such as the chiral nematic, the blue phases and the twist grain boundary phases are known to result from the presence of chiral interactions between the constituent molecules [3]. It should be possible, therefore, to explore the properties of such phases with computer simulations by introducing chirality into the pair potential and this can be achieved in two quite different ways. In one a point chiral interaction is added to the Gay-Berne potential in essentially the same manner as electrostatic interactions have been included (see Sect. 7). In the other, quite different approach a chiral molecule is created by linking together two or more Gay-Berne particles as in the formation of biaxial molecules (see Sect. 10). Here we shall consider the phases formed by chiral Gay-Berne systems produced using both strategies. 

The B4 phase is complex a phase seemingly dominated by defects, similar to the cholesteric blue phase. While the detailed structure is not known, some facts are clear. From the viewpoint of this discussion, the key observation is the chirality of domains of the B4 phase in 4-. im LC cells. This... 

Liquid crystal display technology, 15 113 Liquid crystalline cellulose, 5 384-386 cellulose esters, 5 418 Liquid crystalline conducting polymers (LCCPs), 7 523-524 Liquid crystalline compounds, 15 118 central linkages found in, 15 103 Liquid crystalline materials, 15 81-120 applications of, 15 113-117 availability and safety of, 15 118 in biological systems, 15 111-113 blue phases of, 15 96 bond orientational order of, 15 85 columnar phase of, 15 96 lyotropic liquid crystals, 15 98-101 orientational distribution function and order parameter of, 15 82-85 polymer liquid crystals, 15 107-111 polymorphism in, 15 101-102 positional distribution function and order parameter of, 15 85 structure-property relations in,... 

Experimental evidence was reported for the existence of various additional phases a pre-cholesteric order in the form of a network of double-twisted cylinders, analogous to the thermotropic blue phases [27], a hexatic phase that replaces the hexagonal columnar in very long DNA fragments [31], and a structure with orthorhombic symmetry appearing in the transition to crystalline order [27]. 

Although the Prussian blue phases exhibit remarkable magnetic properties, their face-centred cubic structures mean that no magnetic anisotropy can be expected. 

Fig. 18 Evolutionary Distribution Plot for the GA structure solution of the a phase of L-glut-amic acid. Structures produced by mating events are shown as blue squares, structures produced by mutations are shown as green diamonds, and structures passing unchanged from the previous generation are shown as red circles...

Whether quasicrystalline structures are limited to alloys remains an open question. It is possible that their occurrence is much more widespread than had been previously thought. Indeed there is evidence for quasicrystallinity in both thermotropic and lyotropic liquid crystals. Diffraction patterns of decagonal symmetry have been recorded in lyotropic liquid crystals [K. Fontell, private communication], (Fig. 2.19), and there is theoretical evidence for the existence of a quasicrystalline structure within the blue phase of cholesterol (Chapters 4, 5). (The decagonal structure has quasisymmetry perpendicular to the tenfold axes, and translation symmetry along them.) Viruses crystallise in icosahedral clusters and the list continues to grow. In addition to five-fold symmetry, it has been shown that eight and ten- fold quasisymmetry is possible. ... 

Hgure 4.33 Representation of the local structure of some chiral mesophases on heating. The matches describe the relative orientations of chiral molecules in space. As the temperature is raised, the system transforms from a crystalline phase (left) to a cholesteric phase (centre) characterised by a single twist, to a double-twist blue" phase (right). 

The structure of the blue phase is of some importance. Among the lipoproteins carrying lipids in the blood, low-density lipoproteins (LDL) have attracted much attention. They are the factors mainly responsible for plaque formation, which ultimately leads to atheriosclerotic changes and heart disease. The major components of the LDL-particles are cholesterol fatty acid esters. A remarlmble property is the constant size of LDL particles [28], which indicates that the interior must possess some degree of order. It seems probable that the structure proposed above for cholesterol esters in the cholesteric liquid-crystalline structure should occur also in the LDL-particle. In that case the LDL particle can be viewed as a dispersed blue phase, whose size is related to the periodicity of the liquid-crystalline phase, and the protein coat at the surface is oriented parallel to adjacent specific crystallographic planes of the blue phase. These amphiphilic proteins will expose lipophilic segments inwards emd expose hydrophilic groups towards tiie enviroiunent. 

This domain consists of a bundle of a-helices packed in pairs against each other. The most common arrangement is illustrated in Fig. 6.1. The space between the four helices is occupied by hydrophobic side chains, whereas polar side chains are directed towards the surrounding solution. The a-helices are twisted with respect to each other, and their arrangement is similar to that of a fragment of a blue phase (c/. Figure 5.5). In both cases, the chirality of the structural units leads to hyperbolic curvature within the aggregate. 

PolyTCDU (X = C5H5) can be synthesized so that the red, high-temperature phase is stable at room temperature (12). Conversion to the blue phase can be achieved at low temperatures (at least partially) (13) or under a strain field (14). The optical properties of the red aTi blue phases of polyTCDU are nearly identical to those of polyETCD and polylUPDO (9,J ). The X-ray structure of polyTCDU (2 ) suggested that thTs polymer existed in the butatriene conformation, -(R)C C=C=C(R)-, rather than the commonly observed (and theoretically more stable) acetylenic conformation, =(R)C-C5C-C(R)=. This led to the suggestion that thermochromism involved an acetylenic-to-butatrienic conformational change (10). 

Fig. 5 Structures of Blue Phases I and II. The rods in (a) and (c) represent double-twist cylinder. The black lines in (b) and (d) represent disclination lines...

Recently, direct observations of the blue phase lattice structure have been attempted by freeze-fracture electron microscopy [ 13,14] (Fig. 7), atomic force microscopy for quenched blue phases [15], and confocal laser scanning microscopy [ 16] (Fig. 8). 

Recent progress in material science, notably with the development of new materials exhibiting blue phases, has generated a renewed interest in the incorporation of the functional properties with the unique structure of frustrated phases. Synthesis of a monosubstituted ferrocene-based chiral Schiff s base derivative which exhibits TGBA and blue phases has been reported [17] (Fig. 9). Other metallomesogens leading to blue phases have been found for palladium complexes [18] (Fig. 10). Optically active materials incorporating... 

Fig. 12 Chemical structure of T-shaped dimeric liquid crystal molecules that broadened the temperature range of blue phases to 13 K [24]...

Fig. 13 Chemical structure of materials exhibiting a blue phase with a wide temperature...

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