Liquid Crystal Structures

Fig. 13. Lyotropic liquid crystal structures (a) micelle formed by a typical soap (b) vesicle formed by a typical phospholipid.

Similar lamellar structures are formed for l-alkyl-3-methylimida2olium cations with [PdCl4] when n > 12. As with the pyridinium systems, mesomorphic liquid crystal structures based on the smectic A structure are formed [24]. 

Polyphilic Liquid Crystals - Structure and Phase Behaviour. . . 223... 

KEY TERMS supercooled liquid crystal structure silver iodide... 

Mueller-Goymann, C.C., and Frank, S.G., Interaction of lidocaine and lidocaine-hydrochloride with the liquid crystal structure of topical preparations, Int. J. Pharm., 29 147-159 (1986). 

Micelles can be spherical or laminar or cylindrical. Micelles tend to be approximately spherical over a fairly wide range of concentrations above CMC (critical micelle concentration) but often they are marked transitions to larger, non spherical liquid crystal structures at high concentrations. For straight chain ionic surfactants, the number of monomer units per micelle ranges between 30 and 80. 

Charvolin, J. and Tardieu, A. Lyotropic liquid crystals Structures and Molecular Motions, in L. Liebert, ed. Liquid Crystals . Solid State Physics, Supplement 14, Academic Press, New York, NY 1978, p. 209... 

The three fundamental lyotropic liquid crystal structures are depicted in Figure 1. The lamellar structure with bimolecular lipid layers separated by water layers (Figure 1, center) is a relevant model for many biological interfaces. Despite the disorder in the polar region and in the hydrocarbon chain layers, which spectroscopy reveals are close to the liquid states, there is a perfect repetition in the direction perpendicular to the layers. Because of this one-dimensional periodicity, the thicknesses of the lipid and water layers and the cross-section area per lipid molecule can be derived directly from x-ray diffraction data. 

With such low concentrations of components available to form critical nuclei, hydrate formation seems unlikely in the bulk phases. However, at an interface where higher concentrations exist through adsorption (particularly at the vapor-liquid interface where both phases appear in abundance) cluster growth to a supercritical size is a more likely event. High mixing rates may cause interfacial gas + liquid + crystal structures to be dispersed within the liquid, giving the appearance of bulk nucleation from a surface effect. 

Bailey C, Jakli A (2007) Role of molecular shape on bent-core liquid crystal structures. Phys Rev Lett 99 207801... 

The structures of liquid crystals are intermediate between the amorphous and crystalline states. They have some short-range orientational order. Some also have positional order. Thousands of organic compounds exhibit liquid crystal structures. Most have molecules that are very long and thin, but some have molecules that are flat and pancake shaped. Many compounds may exist in more than one liquid crystalline state. Transitions from one state to another may be thermotropic (caused by temperature change) or lyotropic (caused by change of solute concentration). 

Humans use liquid crystals in a variety of ways. The LCD in popular LCD monitors stands for liquid crystal display. Each dot of color in these displays is light passing through a thin layer of liquid crystals. When electricity passes through the layer, the liquid crystal structure is turned and twisted to reflect different colors of light. LCD monitors are particularly popular because they take low amounts of energy to operate. 

Name 2-Ethylhexyl carbonate coated or bonded on cholesteryl silica (room temperature liquid crystal) Structure ... 

The general relationship between the chromatographic selectivity and the liquid crystal structure have not yet been unambiguosly clarified his problem has been studied in greater detail on 4,4-dialkoxyazoxyben-zenes. 

In general, the greater the similarity in size and shape between the solute and liquid-crystalline solvent molecules, the easier it is for the solute to incorporate itself into the liquid-crystalline phase. If the result of a chemical reaction depends on the solvent order, then the largest effects can be expected for those solute molecules which fit best into the liquid-crystal structure. Since the structure of -heptadecyl phenyl ketone is identical to -butyl stearate except for the terminal phenyl and butoxy groups, it exhibits the largest solvent effect of the ketones studied [730]. 

The model materials were obtained under the assumption that silica polymerization is negligible before the ordering of the liquid crystal structure. Such systems have been observed experimentally for silica at very basic conditions or for transition metal oxides at acid conditions. 

The ability of the amphiphilic molecules to maintain their organization and orientation in aqueous medium at a distinct region of temperatures leads to characteristic features of liquid crystal structures. In this mesogenic state, the molecules keep their order and point to a common direction, not as strictly as in the solid state, nor are they able to move as freely as in liquid state. In most liquid crystal structures more than one state is observed in the range of temperatures that the liquid crystal is present. These states are called mesophases and the phenomenon is called polymorphism . 

The presence of liquid crystal structures at both the w-o and o-w interfaces in multiple emulsions has been investigated by Kavaliunas and Frank (31). Microscopic examination of w/o/w emulsions between crossed polarizers revealed the presence of liquid crystal phases at both inner (w-o) and outer (o-w) interfaces in a w/o/w system composed of water, p-xylene and nonylphenol diethylene glycol ether. Liquid crystalline phases were also detected in o/w/o emulsions at both interfaces. The presence of these liquid crystal structures was found to improve the stability of the emulsions markedly. Matsumoto (32, 33) have concluded that the oil layers in w/o/w systems are likely to be composed of or contain,at least in proximity to the aqueous phase,multilamellar layers of the lipophilic surfactant used in the formulation this is postulated in part to explain the rate of volume flux of water through the oily layer. 

This suggests that the ordered structure is present in the resin solution as a liquid crystal and is maintained into the cured state. The presence of a liquid-crystal phase in natural proteins and synthetic polypeptides is well documented. The liquid-crystal structure is the result of an unique conformation which allows a highly ordered hydrogen bonding system to develop. 

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