Liquid-crystalline molecules

Liquid crystal displays depend upon the reorientation of the director , the defining alignment vector of a population of liquid crystalline molecules, by a localised applied electric field between two glass plates, which changes the way in which incident light is reflected directional rubbing of the glass surface imparts a... 

Yamada, M., Shen, Z. and Miyake, M. (2006) Self-assembly of discotic liquid crystalline molecule-modified gold nanopartides control of ID and hexagonal ordering induced by solvent polarity. Chemical Communications, (24), 2569-2571. 

Scheme 19 shows that arylation of spz G-H bonds with aryl iodides can be applied to the synthesis of light-emitting and liquid crystalline molecules.164 The Pd-catalyzed tandem G-H coupling reactions of thiazole with aryl iodides give the differently substituted 2,5-diarylthiazoles, which would be a highly potential single-layer EL method with polarized light emission. 

Reinitzer discovered liquid crystallinity in 1888 the so-called fourth state of matter.4 Liquid crystalline molecules combine the properties of mobility of liquids and orientational order of crystals. This phenomenon results from the anisotropy in the molecules from which the liquid crystals are built. Different factors may govern this anisotropy, for example, the presence of polar and apolar parts in the molecule, the fact that it contains flexible and rigid parts, or often a combination of both. Liquid crystals may be thermotropic, being a state of matter in between the solid and the liquid phase, or they may be lyotropic, that is, ordering induced by the solvent. In the latter case the solvent usually solvates a certain part of the molecule while the other part of the molecule helps induce aggregation, leading to mesoscopic assemblies. The first thermotropic mesophase discovered was a chiral nematic or cholesteric phase (N )4 named after the fact that it was observed in a cholesterol derivative. In hindsight, one can conclude that this was not the simplest mesophase possible. In fact, this mesophase is chiral, since the molecules are ordered in... 

Nuckolls and Katz have synthesized discotic liquid crystalline molecules in which the core is a helix in its own right.37 Nonracemic helicene 33 was found to assemble into a columnar mesophase in which the helicenes stack on top of each other. CD spectroscopy showed a strong increase of the Cotton effect upon going from the molecularly dissolved state to the aggregated state, exhibiting an amplification of chirality. These helical columns give rise to a strong expression of chirality because the intrinsic shape of the helicenes... 

Attaching non amphiphilic or amphiphilic liquid crystalline molecules as side chains to linear, branched or crosslinkedpolymers yields liquid crystal (l.c.) side chain polymers, which can exhibit the liquid crystalline state analogously to the conventional low molar mass liquid crystals. The l.c.-side chain polymers combine the specific, anisotropic properties of the liquid crystalline state with the specific properties of polymers. 

Following the general scheme of the basic structural elements of rod-like liquid crystalline molecules, the donor atom or set of donor atoms can be... 

Finally, we consider the method for anisotropic ionic conductivity. Anisotropic ionic conductivity is a phenomenon that appears in a sample undergoing liquid crystalline phase or micro phase separation. In the nanotechnology field such samples are expected to yield important materials because they can raise the value of ion conduction. To measure the anisotropic ionic conductivity, one has to design a special cell. Figure 6.5 shows an example of a cell shaped Uke a comb [8]. In the comb-shaped cell, the ionic conductivity is measured between two teeth of the comb. As the liquid crystalline molecules orient perpendicularly on the glass substrate, the ionic conductivity is obtained along with the minor axis. The important task is to prepare the specific phase homogeneously in the measurement cell. The details will soon be presented in published papers. 

A facile synthesis of liquid-crystalline molecules is demonstrated in Scheme 10-4 (see also Section 10.10.4) [19]. 

The covalent linkage of these different classes of molecules to a single linear polymer chain (rod—coil copolymer) can produce a novel class of self-assembling materials since the molecules share certain general characteristics of diblock molecules and rodlike liquid crystalline molecules.12 15 The difference... 

In Chapters 1, 2, and 3 unconventional liquid crystalline molecules with complex structures based on covalent bonding are described. In Chapter 4, Rowan and Mather demonstrate that non-covalent bonding such as hydrogen bonds may be used for the design and construction of liquid crystalline materials. 

If the liquid crystalline molecules are not cylindrically symmetrical, S must be expressed by a tensor (traceless tensor). The nematic liquid crystal state (a uniaxial symmetrical system) is the main concern of the book. For such a phase, the order parameter can be denoted by the scalar in Equation 1.11. 

According to the elastic continuum theory of liquid crystals which was introduced in Chapter 1, the three kinds of deformations can be described by three elastic constants, An(splay), / (twist) and / (bend). In the case of small molecular mass liquid crystals, the three constants are mainly determined by the chemical composition of the liquid crystalline molecules. Among them, K22 is the smallest while the other two are approximately close. All three elastic constants are of the order of 10 12 N. The elastic constants of some important liquid crystals are listed in Table 6.1. Each kind of liquid crystals is a mixture of R5-pentyl and R6-hexyl homologues in the ratio of 40 60. The data are obtained at the temperature of T = Tc — 10 °C where Tc is the clear temperature. 

Discotic liquid crystals came to prominence in the late 1970s when Chandrasekhar, Sadashiva, and Suresh reported the discovery of this new class of liquid-crystalline molecules, which were found to form columnar phases. The first of these, a hexaalkanoate of benzene, is shown in Figure 9. There then followed a rather unfortunate confusion of nomenclature in which the phases formed by discotic molecules were themselves referred to as discotic, carrying the abbreviation D. A liquid-crystal phase must be characterized by its symmetry and organization and not the shape of the molecules of which it is composed this is particularly important in columnar systems as many non-discotic molecules exhibit columnar phases. Indeed, columnar mesophases have been recognized for many years and studies date back to at least the 1960s with the work of Skoulios with various metal soaps. " Therefore, columnar phases take the abbreviation Col followed by some descriptor that describes the symmetry of the phase. 

Figure 9.12. Schematic representation of (a) a standard twisted-nematic liquid crystal display and (b) a related display equipped with a drawn nanocomposite. 1, incoming light (unpolarized) 2, polarizer 3, glass plate coated with an electrode layer and an orientation layer for the liquid-crystalline molecules 4, liquid-crystalline molecules forming a 90° helical twist in absence of a voltage or a linear array parallel to an electric field in presence of an electric field 5, nanocomposite with oriented arrays of metal particles. See color insert.

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