Lyotropic mesomorphous systems

Tihe term lyotropic mesomorphism is used to describe the formation of thermodynamically stable liquid crystalline systems through the penetration of a solvent between the molecules of a crystal lattice. In contrast to the thermotropic mesomorphism shown by many pure substances, lyotropic mesomorphism always requires the participation of a solvent. Lyotropically mesomorphous systems, however, are usually as sensitive to changes in temperature as thermotropic systems. So far, lyotropic mesomorphism has been observed almost exclusively in lipid systems containing water. Lipids that show lyotropic mesomorphism frequently... 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

Multicomponent Systems. There are many mesomorphic systems in which at least two components are present. The most common variety is called a lyotropic mesophase it consists of a molecule with a hydrophilic and a hydrophobic portion dissolved in water. Since at least two components are present, there can be a coexistence of more than one phase. The classical method of investigating such systems consisted of mixing the two components together, centrifuging until the two phases were separate, and analyzing each phase. By NMR it is possible to make a qualitative analysis of each phase without separation in many cases. The sodium palmitate (NaP)-deuterium oxide (D20) system shows the sort of information which can come from such an analysis. The NaP-D20 system exists in several different mesomorphic phases in addition to the isotropic liquid and crystalline phases (6, 23, 36, 37). The mesophases are mainly of the smectic type although the lyotropic mesophase normally called middle does not have all the characteristics of a true smectic phase. 

The design of an amphiphilic system due to non covalent binding strongly depends on the right choice of "complementary" components which is based on the well known ideas of the lyotropic mesomorphism. That is why we discuss here the structure and phase behavior of poly-and dicarboxylic acids complexes with tertiary amines (jS-N-dimethylamino-4-alkyl-and alkyloxypropiophenones) and amine hydrochlorides having the following structure ... 

In the field of natural products, there is growing interest in the increasing range of carbohydrates that are being found to be liquid crystalline [78-80], swinging interest back to the role of liquid crystals in biological systems, where recent studies of lyotropic mesomorphism in deoxyguanosine... 

The importance of the liquid crystal order in living systems and in model substances is well documented. The lyotropic mesomorphism usually observed in these systems is generally related to the presence of amphiphilic moieties embedded in an intrinsically chiral environment that may cause chiral smectic or, more frequently, cholesteric states. However, any comment on this special area is outside the scope of the present paper,... 

A compound which displays liquid crystal properties is referred to as a mesogen and said to exhibit mesomorphism. Liquid crystals may be considered either as disordered solids or ordered liquids, and their properties are very dependent on temperature and the presence or absence of solvent. In thermotropic liquid crystals the phases of the liquid crystals may be observed to change as the temperature is increased. In lyotropic liquid crystals the ordered crystalline state is disrupted by the addition of a solvent, which is very commonly water. For these systems temperature changes may also be... 

Pc macrocycle. Some of them are mesomorphic and show a Colh phase (Fig. 79 I-Gl G 115 Coin 270 I II-Gl G <-20 Colh > 320 h H-G2 G 115 Colh 250 I II-G3 94 Colh 108 I) for which the structure of the columnar mesophase is frozen at room temperature (anisotropic glasses). The functionalization of these dendrons in the 3 and 5 position of the terminal rings by oligo(ethyleneoxy) chains (0CH2CH2)30CH3, and their subsequent grafting onto the phthalocyanine of type I (Fig. 79) led to amphiphiUc materials [333]. In concentrated ethanol solutions ( 20-40% by mass), the compound with the fimctionaUzed G1 dendron behaves as a discotic amphiphUe forming a coliunnar nematic lyotropic phase. In addition, it possesses a columnar mesophase stable from room temperature up to 260 °C. Systems of type III are not mesomorphic. 

Lipids constitute a diverse and important group of biomolecules. Most lipids can behave as lyotropic liquid crystals. In the presence of water, they self-assemble in a variety of phases with different stmcture and geometry. The lipid polymorphic and mesomorphic behavior, i.e., their ability to form various ordered, crystalline, gel, or liquid-crystalline phases as a function of water content, temperature, and composition, is one of the most intriguing features of lipid-water systems. The mutual transformations between these phases and their physiologic implications are the subject of this article. 

Isotropic polymeric systems as well as particulate systems might also show time-dependent moduli after cessation of flow. As long as the shear does not induce structure growth, the moduli always increase with time after flow. An increase of the moduli upon cessation of flow has also been reported for thermotropic PLCs (18) as well as for lyotropic solutions of hydroxy propyl cellulose in water (19) and in acetic add (20). The possibility of changing in either direction seems to be characteristic for mesomorphic materials. A fundamental theory for describing complex moduli does not exist for such materials. The present results, combined with the information about optical relaxation mentioned above, could be explained on the basis of reorientation of domains or defects. The different domains orient differently, even randomly, at rest whereas flow causes an overall orientation. Depending on the molecular interaction the flow could then cause an increase or decrease in moduli as recently suggested by Larson (21). 

The dipalladium organyls 51, derived from 49 (M = Pd, X = C1) by ligand exchange reaction between the bridging group and acetylacetonate, are not mesomorphic in their pure state, but form mesomorphic charge transfer systems with the electron acceptor TNF [95]. The identity of the induced mesophase is still unknown, but seems very likely to be columnar [96]. Furthermore, lyotropic nematic phases were obtained in the ternary mixture 51/TNF/linear alkane (the binary mixture 51/alkane did not yield mesomorp-hism). The nematic phase in this system is though to have a columnar nature, namely a nematic columnar phase. 

A basic understanding of the structure and behavior of liquid-crystalline cellulosics has yet to evolve. From a conceptual point of view, the chirality of the cellulosic chain is most sensitively expressed in the super-molecular structure of the cholesteric phase, which may be described by the twisting power or the pitch. At present, no information is available about domains or domain sizes (correlation lengths) of supermo-lecular structures. The chirality in the columnar phases has not been addressed at all. The principal problem, i.e., how does chirality on a molecular or conformational level promote chirality on the supermolecular level, has not been solved. If this correlation were known, it would enable the determination of the conformation of cellulosic chains in the mesomorphic phase and the development of models for the polymer-solvent interactions for lyotropic systems. On the other hand, direct probing of this interaction would provide a big leap towards an understanding of lyotropic phases. 

The solution properties of these materials are unusual. They form optically anisotropic solutions in both amide and acid solvent systems over quite wide ranges of concentration and polymer molecular weight. In other words they are among the few known examples of synthetic polymers which can form lyotropic liquid crystals. (That is to say liquid crystals formed by the action of a solvent.) The usual example quoted in this context is poly(y-benzyl-L-glutamate) which forms cholesteric mesomorphic solutions in certain organic solvents. The helical structure adopted by the polypeptide in these solvents behaves as a rigid rod and it is... 

Sadron et al. (l) prepared lyotropic liquid crystalline systems using polymers and a polymerizable solvent and attempted to fix the mesomorphic structure by polymerizing the monomeric solvent. Bouligand et al. (2) attempted to prepare liquid crystalline substances with fixed structure by copolymerizing mono- and bifunctional mesomorphic monomers. However neither group investigated the phase conditions of the monomers or of the monomer and polymer. In both cases identical homogeneous phases were assumed before and after polymerization. 

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