Blue phases smectic

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. 

New chiral phases, called smectic blue phases (BPSm), have been discovered in a small temperature range with the following phase sequence TGB-BPsml-BPsm2-BPsm3-Iso, without any intermediate chiral nematic phase between the BPSm and TGB phases [27,28]. X-ray scattering studies showed that unlike the traditional blue phases, the smectic blue phases possess the quasi-long-range smectic order in addition to three-dimensional orienta-... 

Fig. 14 Image of smectic blue phase based on uniform layer spacing of the Schwartz P surface [38]...

Chirality is also an important aspect of liquid crystals. The introduction of chiral moieties into the chiral smectic phases induces functions such as ferroelectricity and antiferroelectricity. A few of the unconventional chiral liquid crystals are described in Chapter 1. The blue phase is one of the exotic chiral liquid crystalline phases. In Chapter 3, Kikuchi introduces the basic aspects and recent progress in research of the blue phase. Recently, the materials exhibiting the blue phases have attracted attention because significant photonic and electro-optic functions are expected from the materials. 

The heat of the clearing point transition ( 7-9 kj moK ) is typical for a smectic to isotropic transition, and two orders of magnitude higher than for Blue phase isotropic transitions. 

Since the discovery of the first liquid crystalline material in 1888, helicity has proven to be one of the most fascinating topics in this field."" Several liquid crystalline phases with helical structure were reported, such as chlolesteric phase, blue phase, ferroelectric and antiferro-electric smectic phases, and helical smectic A phase. In most of these helical phases, at least a fraction of the constituent molecules have an asymmetric carbon, and it was long believed that chirality at a molecular level is a prerequisite to construct chiral architectures at the mesoscopic level. However, Watanabe et al. reported the first example of spontaneous helix formation in liquid crys-... 

The reports on photoresponsive chiral LCs can be traced back to the 1960s and 1970s, during which a number of examples on photomning of pitch length in cholesteric phases were demonstrated [5-7]. To date, numerous reports have been found to be related to their physics, chemistry and applications. This chapter mainly deals with the recent progress in this area with a survey of three major classes of chiral LC phases, i.e. cholesteric (N ), chiral smectic C (SmC ) and blue phase (BP) from their stmctures to properties and applications. 

LC phase, while the later systems are based on chirality amplification mechanism. There are many types of chiral LC phases such as cholesteric (N ), chiral smectic (Sm ), blue phase (BP), and twist grain boundary (TGB) phase. Among them, N and SmC phases are the most studied due to their potential technological applications. BPs are also receiving increasing attention due to their interesting 3D cubic structures and potential applications as 3D photonic crystals. 

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

It seems that no investigation has been carried out on nonlinear optical effects in more ordered smectic phases, polymeric liquid crystals or in blue phases. Some... 

The blue phases BP I and BP II, which appear in a narrow temperature range between the cholesteric and isotropic phase, are not birefringent but optically active. In the transmitted light of a polarizing microscope they look like a blue isotropic liquid. Sometimes small single crystals of the blue phase with distinct habit are seen. The polycrystalline blue phase platelet texture resembles the mosaic texture of the smectic B phase. 

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. 

Figure 1.13. Helical structures formed in chiral liquid crystals, (a) Cholesteric phase (N ), (b) blue phase (BP), (c) chiral smectic-C phase (SmC ), and (d) twist grain...

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. 

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