Liquid crystalline state properties

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

The liquid crystalline state may be identified as a distinct and unique state of matter which is characterised by properties which resemble those of both solids and liquids. It was first recognised in the middle of the last century through the study of nerve myelin and derivatives of cholesterol. The research in the area really gathered momentum, however, when as a result of the pioneering work of Gray in the early 1970 s organic compounds exhibiting liquid crystalline properties were shown to be suitable to form the basis of display devices in the electronic products. 

Unusual properties of fully aromatic polyesters are observed if they have at least partially a rigid planar chain structure. In particular, they can form thermotropic liquid crystalline states (see Example 4-5). As already discussed in Sect. 1.2.4 an important structural prerequisit for LCPs of Type A in order to attain the liquid crystalline state of aromatic polyesters (and aromatic polyamides, see Example 4-14), is a rigid main chain according to the following construction principle ... 

From a practical point of view, the deviation from main-chain continuity is the most interesting one. Especially the concept of the so-called parallel offset of the main chain is favorized. It is realized in a commercial product made from 4-hydroxybenzoic acid and 2,6-hydroxynaphthalenecarboxylic acid. The incorporation of small amounts of 2,6-hydroxynaphthalenecarboxylic acid causes a discontinuity in the main chain but only in form of a parallel offset of some chain segments. Thus, the ability to form liquid crystalline states is largely maintained as well as the anisotropic properties of the molten and solid polyester. Instead, the melting point is significantly reduced, as desired. 

Although the majority of the lipids in M. laidlawii membranes appear to be in a liquid-crystalline state, the system possesses the same physical properties that many other membranes possess. The ORD is that of a red-shifted a-helix high resolution NMR does not show obvious absorption by hydrocarbon protons, and infrared spectroscopy shows no ft structure. Like erythrocyte ghosts, treatment with pronase leaves an enzyme-resistant core containing about 20% of the protein of the intact membrane (56). This residual core retains the membrane lipid and appears membranous in the electron microscope (56). Like many others, M. laidlawii membranes are solubilized by detergents and can be reconstituted by removal of detergent. Apparently all of these properties can be consistent with a structure in which the lipids are predominantly in the bilayer conformation. The spectroscopic data are therefore insufficient to reject the concept of a phospholipid bilayer structure or to... 

Properties have been determined for a series of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and poly [3,3-bis(methoxymethyl)oxetane]-(ro-tetrahydrofuran. The block copolymers had properties suggestive of a thermoplastic elastomer (308). POX was a good main chain for a well-developed smectic liquid crystalline state when cyano- or fluorine-substituted biphenyls were used as mesogenic groups attached through a four-methylene spacer (309,310). Other side-chain liquid crystalline polyoxetanes were observed with a spacer-separated azo moiety (311) and with laterally attached mesogenic groups (312). 

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. 

Ringsdorf investigated the photochemical properties of 89c carrying six cinnamoyl substituents around the [18]-N6 core [115]. Upon irradiation of E-89c in its liquid crystalline state with UV light, the mesomorphism was lost after a short time due to isomerization of the double bond (way A in Scheme 52). This showed... 

This Chapter will present the actual chromophores of vision, labeled the Rhodonines and derivable from a number of feedstocks, including the retinol family, consist of relatively small molecules with a molecular weight of either 285 (R5 R9) or 299 (R7 R11). They are retinoids of the resonant conjugate type. They are also carboxylic-ion systems and exhibit a negative charge in their fundamental form. The molecules are relatively easily generated in the laboratory in pure form. However, they exhibit a number of unique properties that have made their isolation difficult. They only exhibit the properties of a visual chromophore when in the liquid crystalline state. Their absorption characteristic is a transient one unless a means of de-exciting the molecules of the liquid crystal is present. Finally, they are extremely sensitive to destruction by oxidants and alkali metal ions. 

Brown, G. (1977) Structures and properties of the liquid crystalline state of matter. J. Colloid Interface Sci. Vol. 58, pg. 534... 

Hydronium is a liquid crystalline state of water found under a variety of special conditions. It is usually described as a macromolecule. It is crucial to the operation of the animal nervous system due to its specific electronic properties. When used as the base material in the Activas of the neural system, the hydronium liquid crystal has a thickness of less than 100 Angstrom. Hydronium is a n-type semiconductor material with a significant hole velocity in its valence band relative to the electron velocity in its conduction band. 

The most important characteristics of the Rhodonines are not their hormonal properties, as in the case of the retinenes, but their electronic properties, especially when in the liquid crystalline state. These properties are not directly relatable to their relatives, the retinenes. They are more closely associated with another group of relatives, the oxonols. The oxonols consist of two oxygen atoms connected by a conjugated carbon chain. The oxonols and the phthaleins are members of the carboxylic acid family, a large well-known family of dyes. ... 

As discussed in previous paragraphs, the spectral absorption of the chromophores of vision is much more comphcated than that described by Beer s Law for true solutions of low molarity. The absorption of the chromophores of vision is a function of the environment, the chemical state, the spatial relationship, and the orientation of the molecules. They actually exhibit additional, and generally dominant, absorption spectra in the liquid crystalline state that are not found for the same material in low molarity solution. These additional spectra are highly anisotropic. They also exhibit a high absorption coefficient along the preferred axis. Because of these properties, it is extremely difficult to make a comparison of the properties of the chromophores when they are in-vivo with their properties when in-vitro. Because the chromophores are not in solution, when in-vivo, it is not appropriate to use Lambert-Beer s Law to evaluate them (See Section 5.3.5.3), The results of using this law are generally spurious. 

The Rhodonines, when in the liquid crystalline state, are complete chromophores. They need not be associated with any other material to accomplish the absorption process. When still suspended in a liquid medium, they will not, as a large group, display any unique polarization properties. If they are brought to an ever higher level of concentration in a liquid, they will form a gel which will exhibit preferred polarization planes. They can also be precipitated onto a surface after which they will exhibit preferred planes of polarization. They can be precipitated onto glass as well as a protein substrate. They must, of course, be associated with some type of nervous tissue in order to generate the necessary nerve signals. This is clearly not a role for opsin, defined as a protein, to play. 

Properties of a substance in the liquid-crystalline state are intermediate between those of a liquid and a crystalline solid. Like liquids, Hquid crystals are characterized by the absence of long range translational order. However, in the liquid-crystalline phase molecules still preserve a long range orientational order, i.e. like crystalline solids, liquid crystals are anisotropic. 

In order to understand the basic principles of operation of the many different kinds of LCDs being developed and/or manufactured at the present time, it is necessary to briefly describe the liquid crystalline state and then define the physical properties of direct relevance to LCDs. First, the nematic, smectic and columnar liquid crystalline states will be described briefly. However, the rest of the monograph dealing with liquid crystals will concentrate on nematic liquid crystals and their physical properties, since the vast majority of LCDs manufactured operate using mixtures of thermotropic, non-amphiphilic rodlike organic compounds in the nematic state. 

Liquid crystals, due to the presence of the ordered domains, are optically anisotropic, i.e. birefringent. This can be easily verified by observing the liquid crystal, e.g. aramid and sulfuric acid solution, at rest between crossed polarizers. The parallel arrays of polymer chains in liquid crystalline state become even more ordered when these solutions are subjected to shear as, for example, in extruding through a spinneret hole. It is this inherent property of liquid crystal... 

Some Properties of Polymeric Systems in the Liquid Crystalline State. . 89... 

It was found that when a certain concentration is attained, the solutions of these polymers acquire thermodynamically stable properties of anisotropy, still retaining relatively high mobility, i.e. they exhibit the properties typical of the liquid crystalline state. 

Before these results were published, polymer physicists and chemists mainly investigated only two phase-states, amorphous and crystalline. At the present time, along with these two states, the third phase-state of condensed systems, i.e. the liquid crystalline state, became very important. Here the situation turned out to be the same as in the case of low molar mass liquid crystals. In spite of the fact that historically the low molar mass substances in liquid crystalline state had been known for about a century, the intensive study of their properties began only after they had found an important practical application owing to a sharp change in optical properties of liquid crystals in electromagnetic fields (for visual displays) and as sensitive temperature indicators (in medicine). 

In order to give a general idea about the appearance of liquid crystalline state and about the properties of the systems containing these polymers, some examples of linear rigid-chain polymers follow ... 

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