Lyotropic blue phases

Lyotropic systems can show chiral phases in the form of cholesteric phases. Asymmetric micelles are the base imit for these phases. Lyotropic blue phases have also been reported [28]. Detailed descriptions of chiral lyotropic phases are given by K. Hiltrop in Chapter 14. 

Luckhurst potential, dimers 816 luminance, guest-host effect 272 lutetium, phthalocyanine ligands 924 lyotropic blue phases, chromonics 998 lyotropic systems... 

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,... 

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. ... 

The current (third) period, which may be called a colonization, involves wide electrooptical investigations of novel effects in ferroelectric liquid crystals [9, 10] and a study of exotic materials like polymeric and lyotropic mesophases, blue phases in cholesterics, well-ordered smectics, and so on. For conventional (nematic and cholesteric) phases the accent was shifted to the optimization of the material properties for electrooptical devices, though novel phenomena like the supertwist effect [11] and a gamma of linear electrooptical effects [12-14] have also been discovered. 

Lecithins and glycolipids are naturally occurring chiral compounds, which can create a big variety of mesophases (lamellar, hexagonal, cubic, ripple, gel phases, etc.). Classical chiral phases like cholesteric or ferroelectric smectic phases are hitherto not reported and, if they were found, they would not be very typical for this class of compounds. Some of the bicontinuous cubic phases may have enantiomeric pure chiral space groups. Further, lyotropic cholesteric and blue phases might be formed (see below). Ordered tilted lamellar phases have been reported for lecithin and other amphiphilic compounds, but the special effects of chirality, like ferroelectric properties or helical order, are unknown. 

Up to now the most extensively investigated chiral lyotropics are the chiral nematics (the historical but not appropriate term cholesteric is avoided in this chapter). The first evidence on this kind of mesophase has been reported by Radley and Saupe in 1978 [9]. Two studies on a lyotropic phase proposed to be analogous to the thermotropic Blue Phase have been published [10], one has been retracted [11] if there is any analogy, it is small. Blinov et al. reported on a nonaqueous chiral lamellar phase with ferroelectric properties experimental evidence for ferroelectricity in lyotropics is difficult to gain because of high electric conductivity and mostly nonuniform sample orientation. Nevertheless, the existence of piezoelectricity was interpreted as a manifestation of ferroelectricity [12]. 

In concentrated solution, DNA fragments can form lyotropic liquid crystal phases. Short fragments behave like rods, and so the formation of liquid crystal phases is possible. On increasing concentration (above 160 mg/ml for 50 nm DNA in physiological salt solutions), cholesteric and hexagonal columnar phases may be observed (see Chapter 5 for a discussion of these structures) Just below the cholesteric phase, a blue phase is sometimes observed. This phase is named for the colour arising from the double twist cylinders that result from the packing of helices onto a cubic lattice. 

In conclusion, electric field effects in liquid crystals is a well-developed branch of condensed matter physics. The field behavior of nematic liquid crystals in the bulk is well understood. To a certain extent the same is true for the cholesteric mesophase, although the discovery of bistability phenomena and field effects in blue phases opened up new fundamental problems to be solved. Ferroelectric and antiferroelectric mesophases in chiral compounds are a subject of current study. The other ferroelectric substances, such as discotic and lyotropic chiral systems and some achiral (like polyphilic) meso-genes, should attract more attention in the near future. The same is true for a variety of polymer ferroelectric substances, including elastomers. 

The structure of the BPIII phase actually resembles the L3 (so-called sponge) phase of lyotropic liquid crystals/ and the smectic blue phases observed and studied recently. Both the sponge and smectic blue phases are optically isotropic, and the smectic blue are optically active as well. Theoretical arguments show that the reason for the defect structure is the negative value of tire saddle-splay elastic constant, K24, which makes the defects energetically favorable. A sketch of the sponge phase and of the smectic blue phase is shown in Figure 6.24. 

Fig. 5.11 Schematic phase diagram of the C50/formamide system, which exhibits a lyotropic SmC analog phase (top) and texture image (bottom), taken at the position in the contact preparation indicated with a blue bar in the phase diagram...

Fig. 5.43 Refined model of the lyotropic SmC analog phase. The hydrophobic part of the bilayers is highlighted in red, the hydrophilic part in purple and the formamide layer in blue (adapted from [17], Copyright 2015 Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.)...

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