Smectic phase chiral

Chiral Smectic. In much the same way as a chiral compound forms the chiral nematic phase instead of the nematic phase, a compound with a chiral center forms a chiral smectic C phase rather than a smectic C phase. In a chiral smectic CHquid crystal, the angle the director is tilted away from the normal to the layers is constant, but the direction of the tilt rotates around the layer normal in going from one layer to the next. This is shown in Figure 10. The distance over which the director rotates completely around the layer normal is called the pitch, and can be as small as 250 nm and as large as desired. If the molecule contains a permanent dipole moment transverse to the long molecular axis, then the chiral smectic phase is ferroelectric. Therefore a device utilizing this phase can be intrinsically bistable, paving the way for important appHcations. 

Several 4-(3-alkyl-2-isoxazolin-5-yl)phenol derivatives that possess liquid crystal properties have also been obtained (533-535). In particular, target compounds such as 463 (R = pentyl, nonyl) have been prepared by the reaction of 4-acetoxystyrene with the nitrile oxide derived from hexanal oxime, followed by alkaline hydrolysis of the acetate and esterification (535). A homologous series of 3-[4-alkyloxyphenyl]-5-[3,4-methylenedioxybenzyl]-2-isoxazolines, having chiral properties has been synthesized by the reaction of nitrile oxides, from the dehydrogenation of 4-alkyloxybenzaldoximes. These compounds exhibit cholesteric phase or chiral nematic phase (N ), smectic A (S4), and chiral smectic phases (Sc ), some at or just above room temperature (536). 

Thisayukta J, Nakayama Y, Kawauchi S, Takezoe H, Watanahe J (2000) Distinct formation of a chiral smectic phase in achiral banana-shaped molecules with a central core based on a 2,7-dihydroxynaphthalene unit. J Am Chem Soc 122 7441-7448... 

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. 

Nematic gels are very interesting systems, thus deserving further study. Actually, these systems are being studied experimentally for applications. Examples are polymer dispersed liquid crystal displays are sometimes dispersed not in a polymer, but in a polymer network. Displays by means of the polymer stabilized cholesteric texture change, are also achieved in crosslinked systems. In addition, the chiral smectic phase has been obtained in such systems as well. Other types of liquid crystal gels have been applied or are expected to be applied in such devices. 

The use of chiral H-bonding components yields stable chiral phases by molecular association [35-37]. For example, a ferroelectric phase derived from a chiral smectic C phase can be induced by the self-assembly of nonferro-electric molecules [35-37]. Complex 11 (n = 8) exhibits a chiral smectic phase from 109 to 123 °C [35]. In this case, the H-bonded mesogen consists of nonmesomorphic chiral benzoic acid and a stilhazole that shows a very narrow temperature range of ordered smectic phases. The value of spontaneous polarization for 11 at 115 °C is 33.0 nC/cm. When the oxygen in the alkoxy... 

Fig. 5. Helical Structures of the chiral nematic and chiral smectic phases...

On the other hand, it has been shown on LMWLCs that the well-known SmC, where the molecules are tilted with respect to the layer normal, is no longer the only possibility to obtain a fluid biaxial phase [63], As a consequence, a strict determination of the chiral smectic phase structure requires not only a careful analysis of the X-ray diagrams obtained on powder as well as on aligned samples, but also a study of the electrooptic response, which allows discrimination between the ferroelectric, the antiferro-electric, and the ferrielectric behavior. 

The most studied chiral smectic phase is ferroelectric SmC phase [18], which is derived from Smectic C (SmC) phase. As shown in Fig. 5.2, the helical twist in SmC results from chiral organization of smectic layers as similar to the formation of N from nematic layers mentioned above. The molecules in each smectic layer... 

The decrease in order parameter in LCs caused by the photoisomerization of azobenzene molecules are also known to induce phase transition from chiral smectic phase to cholesteric phase. This type of transition is mainly observed in chiral mesogenic compounds. In 1999, My et al. conducted a systematic research on the phase transition behavior of a series of chiral azobenzene LCs [44]. A photo... 

A.D.L. Chandani, E. Gorecka, Y. Ouchi, H. Takezoe and A. Fukuda, Anti-ferroelectric chiral smectic phases responsible for the tristable switching in MHPOBC, Jpn. J. Appl. Phys. 28(7), L1265-L1268, (1989). 

T. Imase, S. Kawauchi, J. Watanabe, Conformational analysis of 1,3-benzenediol dibenzoate as a model of banana-shaped molecules forming chiral smectic phases,... 

In the first illustration of the combined DoM-cross-coupling-DreM sequence in material science, rod-shaped chiral mesogens, 247 and 248, have been synthesized, 244—r 245 —r 246 (Scheme 14.47), and shown to display chiral smectic phase C ... 

Scherow.sky, G., Muller, U., Springer, J., Trapp, W., Levelut, A. M., and Davidson, R, Liquid-crystalline side chain polymers containing a chiral spacer unit exhibiting chiral smectic phases, Liq. Cryst, 5, 1297-1306 (1989). 

Rigid macromolecnles form nematic and smectic phases when their eoncerrtration in certain solvents is high enough. There are also chiral phases if the molecules are ehiral. The best examples of this are the rod-like maeromolecules with stmetures based on a single or double helix, which form chiral nematic and chiral smectic phases in solution. 

The form chirahty of all of these chiral smectic mesophases takes the form of a helical stracture, but the helix manifests itself in a different way from the helix in the chiral nematic phase. In addition to being substantially the most commonly exhibited of the tilted chiral smectic phases, the chiral smectic C phase is by far the most important (least ordered and least viscous) in this category. The chiral smectic C phase is employed in the ferroelectric display device (see Chapter 13) but the helix must be unwound. 

Note that compound 8 exhibits a wide range of tilted chiral smectic phases and shows a chiral nematic phase at higher temperature. Despite possessing the S phase, compound... 

The symmetry requirements necessary for ferroelectricity in low-molecular mass compounds, which were discussed in Section 1.1.3, are valid for polymer mesophases too. If a tilted chiral smectic phase is stable after a polymerization process it must be ferroelectric. Following this idea, the first polymer liquid crystalline ferroelectric has been synthesized by Shibayev et al. [160]. Its spontaneous polarization did not differ very much from the precursor monomer [161]. After polyvinylidene fiuoride (PVF2)... 

Aromatic imide groups are known to be nearly planar, rigid, polar, and thermostable. However, aromatic imide structures are also known to be non-mesogen in nature. Poly(ester-amide) (PEI) derived from N- (4 -carboxyphenyl) trimellitimide and aliphatic spacers are not thermotropic, whether the spacer used is chiral or not. Semi-aliphatic spacers are observed to exhibit both a smectic and a nematic LC phase in the resultant thermotropic PEIs. The semi-aliphatic chiral spacers exhibit both chiral smectic phase (A or C ) and cholesteric phase. Such a chiral smectic LC-phase, which may be ferroelectric in nature, is extremely rare for LC-main-chain polymers [27]. It is a particular advantage of polar imide mesogens to favor the formation of layer-structures when combined with non-polar species [28]. 

Reeves et al. argued that a dispersion type of interaction between single chiral molecules in adjacent micelles is rather imlikely to be essential for the phase chirality [35], Dispersion interactions between colloidal particles, as well as between single molecules, decrease with a strong power of the interparticle distance d (by d to d ). In thermotropic cholesteric or chiral smectic phases the interparticle distance is of the order of 100 pm which is small compared to the typical values of 1 to 10 nm between micelles in lyotropic chiral nematic phases. 

The helical structure which can develop in thick cells of chiral smectic C phases having planar surface alignment conditions can be used to obtain measurements of the components of the dielectric permittivity tensor [29], but the technique is restricted to chiral smectic phases. Measurements are made (see Fig. 9) of the homeotropic state, as above, and additionally the helical state (Fig. 12), and the uniformly-tilted state ob-... 

Molecular ordering and electrooptic switching in chiral smectic phases are discussed in detail elsewhere (see Chap. VII, Sec. 9 of this Volume). In the case of ferroelectric switching in chiral smectic C phases, the direetor n is free to move about a cone of angles which is centered on the horizontal axis. Each molecule has a ferroelectric dipole P, which is perpendicular to its length. This is depicted in Fig. 3. 

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