Blue phases

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Discotic blue phases Discotic liquid crystals Discover Disc Tube... 

A similar effect occurs in highly chiral nematic Hquid crystals. In a narrow temperature range (seldom wider than 1°C) between the chiral nematic phase and the isotropic Hquid phase, up to three phases are stable in which a cubic lattice of defects (where the director is not defined) exist in a compHcated, orientationaHy ordered twisted stmcture (11). Again, the introduction of these defects allows the bulk of the Hquid crystal to adopt a chiral stmcture which is energetically more favorable than both the chiral nematic and isotropic phases. The distance between defects is hundreds of nanometers, so these phases reflect light just as crystals reflect x-rays. They are called the blue phases because the first phases of this type observed reflected light in the blue part of the spectmm. The arrangement of defects possesses body-centered cubic symmetry for one blue phase, simple cubic symmetry for another blue phase, and seems to be amorphous for a third blue phase. 

If the molecules are chiral or if a chiral dopant is added to a discotic Hquid crystal, a chiral nematic discotic phase can form. The director configuration ia this phase is just like the director configuration ia the chiral nematic phase formed by elongated molecules (12). Recendy, discotic blue phases have been observed. 

The electrolyte salt must be processed to recover the ionic plutonium orginally added to the cell. This can be done by aqueous chemistry, typically by dissolution in a dilute sodium hydroxide solution with recovery of the contained plutonium as Pu(OH)3, or by pyrochemical techniques. The usual pyrochemical method is to contact the molten electrolyte salt with molten calcium, thereby reducing any PUCI3 to plutonium metal which is immiscible in the salt phase. The extraction crucible is maintained above the melting point of the contained salts to permit any fine droplets of plutonium in the salt to coalesce with the pool of metal formed beneath the salt phase. If the original ER electrolyte salt was eutectic NaCl-KCl a third "black salt" phase will be formed between the stripped electrolyte salt and the solidified metal button. This dark-blue phase can contain 10 wt. % of the plutonium originally present in the electrolyte salt plutonium in this phase can be recovered by an additional calcium extraction stepO ). 

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. 

Fig. 16a-c. The model proposed for blue phase II showing a,b the director arrangement within a double twist cylinder c the packing of these cylinders along three orthogonal axes... 

The introduction of a second chiral atom in the system leads to a reduction in the mesogenic properties and only a monotropic chiral nematic transition is observed for compound 23. However, when this compound is cooled down from the isotropic liquid state at a cooling rate of 0.5 °Cmin , very unusual blue phases BP-III, BL-II and BP-I are observed in the range 103-88 °C. Blue phases usually require pitch values below 500 nm. Hence the pitch value of the cholesteric phase for 23 must be very short, suggesting that the packing of two chiral carbons forces a faster helical shift for successive molecules packed along the perpendicular to the director. 

Bayon, R., Coco, S. and Espinet, P. (2002) Twist-Grain Boundary Phase and Blue Phases in Isocyanide Gold(I) Complexes. Chemistry of Materials, 14, 3515-3518. 

Similar MMCT transitions occur for phases in certain systems Lu203-M(IV)02. As early as 1915 the name Ceruranblau (cerium-uranium blue) was given to a dark blue phase with approximate composition 2Ce02 UO2 [76]. The electron exchange equilibrium seems to be [6,77] U(IV) -H Ce(IV) < U(V) Ce(III). 

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... 

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Yasuda A, Yoshizawa M, Kobayashi T (1993) Fluorescence spectrum of a blue-phase polydiacetylene obtained by probe saturation spectroscopy. Chem Phys Lett 209 281-286... 

Figure 13.22. Dependence of the Texas Red Hydrazide/Bromothymol Blue phase angle on pH.

Note 2 The name blue phase derives historically from the optical Bragg reflection of blue light but, because of larger lattice constants, BPs can reflect visible light of longer wavelengths. 

Note 3 With chiral nematic substances forming chiral nematic mesophases of short pitch (<700 nm), up to three blue phases occur in a narrow temperature range between the chiral nematic phase and the isotropic phase. 

The complexes bearing one chiral substituent display a smectic A mesophase when the non-chiral chain is long, or an enantiotropic cholesteric and a monotropic SmA phase for shorter alkoxy chains. A TGBA phase is observed for the derivative which contains the chiral isocyanide combined with the diethyloxy, when the SmA to cholesteric transition is studied. The compound with two chiral ligands shows a monotropic chiral nematic transition. When this compound is cooled very slowly from the isotropic liquid it exhibits blue phases BP-III, BP-II, and BP-I. 

By addition of each of several diesters of isosorbide, isomannide, and isoidide to a nematic phase, cholesteric phases can be produced. All compounds exhibit a large twisting power. In the cholesteric phase, helix inversion, large or small temperature-dependencies of the pitch, and broad blue phases were achieved.183... 

A different phenomenon is the appearance of the so-called blue phases in case of chiral LC s, first observed at cholesteric LC s. Sometimes, one or more blue phases occur close below the clearing point with a very small phase width and bright blue or green colours. Figure 15 shows some typical representatives containing one or more X=Y groups in... 

In this report, vacuum evaporated PDA(12-8) film is used as an optically nonlinear layer with a grating coupler for nonlinear coupling for all optical bistability. Grating coupler on a substrate was prepared at the same periodicity and depth as the SHG devices. Vacuum evaporation of PDA on a substrate with previously rf-sputtered Corning 7059 buffer layer film were carried out at 5 x 10 5 torr with tungsten boat heater. Rapid evaporation can avoid thermal polymerization of the undesirable red phase PDA during the process. UV polymerization of the film for the useful blue phase PDA was carried out by Xe lamp 500 w for 20 min. at a... 

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]. 

Stabilization of Blue Phase by Bent-Core Molecules. 309... 

Fig. 5 Induction of the blue phase by doping a N material with (a) a rod-shaped molecule MHPOBC and (b) a bent-shaped molecule P8-PIMB. In both cases, the blue phase is induced above the N phase. The bent-shape of the antiferroelectric molecule is responsible for the blue phase induction in (a), since the doping of a real rod-shaped molecule (TBBA) does not induce the blue phase [26]...

Nakata M, Takanishi Y, Watanabe J, Takezoe H (2003) Blue phases induced by doping chiral nematic liquid crystals with non-chiral molecules. Phys Rev E 68 041710-1-6... 

Alexander GP, Yeomans JM (2006) Stabilizing the blue phases. Phys Rev E 74 061706-1-9... 

Hur S-T, Gim M-J, Yoo H-J, Choi S-W, Takezoe H (2011) Enhanced thermal stability of liquid crystalline blue phase I with decreasing bend and splay elastic constant ratio K33/K11. Soft Matter, in press (DOI 10.1039/clsm06046e)... 

Taushanoff S, Le KV, Williams J, Twieg RJ, Sadashiva BK, Takezoe H, Jakli A (2010) Stable amorphous blue phase of bent-core nematic liquid crystals doped with a chiral material. J Mater Chem 20 5893-5898... 

Le KV, Aya S, Sasaki Y, Choi H, Araoka F, Ema K, Mieczkowski J, Jakli A, Ishikawa K, Takezoe H (2011) Liquid crystalline amorphous blue phase and its large electrooptical Kerr effect. J Mater Chem 21 2855-2857... 

Lee M, Hur S-T, Higuchi H, Song K, Choi S-W, Kikuchi H (2010) Liquid crystalline blue phase I observed for a bent-core molecule and its electro-optical performance. J Mater Chem... 

Zero-Dimensional Nanoparticle Additives in Blue Phases... 

In the past, blue phases largely remained a subject of scientific curiosity, because for many years the rather limited temperature range (commonly from 0.5 to 2°C) severely restricted further scientific exploration as well as practical use of these intriguing phases. Early work on blue phases primarily focused on new materials [379-392], their response to electric fields [393 -06], the shape of blue phase crystals grown for example under an applied electric field [407 -09], as well as lasing in blue phases [410]. 

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