Lyotropic liquid-crystalline systems

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

The mixing of nematogenic compounds with chiral solutes has been shown to lead to cholesteric phases without any chemical interactions.147 Milhaud and Michels describe the interactions of multilamellar vesicles formed from dilauryl-phosphotidylcholine (DLPC) with chiral polyene antibiotics amphotericin B (amB) and nystatin (Ny).148 Even at low concentrations of antibiotic (molar ratio of DLPC to antibiotic >130) twisted ribbons are seen to form just as the CD signals start to strengthen. The results support the concept that chiral solutes can induce chiral order in these lyotropic liquid crystalline systems and are consistent with the observations for thermotropic liquid crystal systems. Clearly the lipid membrane can be chirally influenced by the addition of appropriate solutes. 

In principle, lyotropic liquid crystalline systems are such systems in which liquid crystalline ordering appears only in the presence of a solvent, the solvent being selective and the dissolved substance having amphiphylic properties. Soaps, lipids, and some dyes in an aqueous medium may serve as examples of such systems. 

The purpose of this paper is to explore various aspects of the rheological behaviour of lyotropic liquid crystalline systems. Lyotropics are often used as model systems for thermotropics because their viscoelastic behaviour seems to be quite similar (1) and solutions are much more easier to handle and can be studied more accurately than melts. The emphasis is on transient data as these are essential for verifying viscoelastic models but are hardly available in the literature. Transient experiments can also provide insight in the development of flow—induced orientation and structure. The reported experiments include relaxation of the shear stress and evolution of... 

Zugenmaier, P. Haurand, P. Structural and rheological investigations on the lyotropic, liquid-crystalline system 0-ethylcellulose-glacial acetic acid-dichloroacetic acid. Carbohydr. Res. 1987, 160, 369-380. 

Siekmeyer, M. Zugenmaier, P. Investigations of molar mass dependence of the lyotropic liquid-crystalline system cellulose tricarbanilate/ diethylene glycol monoethyl ether. Makromol. Chem. Rapid Commun. 1987, 8 (10), 511-517. 

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. 

The influence of photoinitiator mobility and solubility on the free-radical polymerization behavior in lyotropic liquid crystalline systems was also investigated. In this study common photoinitiators were used. They were two commercial materials ... 

Up to now, only the structural demands on the surfactant were considered. But as the solvent is the second important component of the lyotropic liquid crystalline system, the nature of the solvent has to be reflected, too. Thus, to learn more about the role of the solvent, contact preparations of C50 and diverse hydrophilic solvents were screened. The schematic phase diagrams obtained will be discussed in the following section. 

Besides water, typical solvents used in literature for lyotropic liquid crystalline systems are ethylene glycol and formamide [11, 12]. This is not surprising, as all of these solvents are polar protic solvents and thus share a couple of properties, e.g. a low molecular weight, a highly polar stmcture and the ability to form hydrogen bonds [13]. To gain further insight into the influence of the solvent s chemical stmcture on the formation of the lyo-SmC phase, additional solvents were used. 

Metallo phthalocyanine units as dye components are fixed on lyotropic liquid crystalline systems based on poly(y-benzyl-L-glutamate). Phthalocyanines are introduced onto the liquid crystalline backbone of poly(y-benzyl-L-glutamate) as shown in Figure 17.13 via a Friedel-Crafts reaction of acid chloride of phthalocyanine tetra-carboxylic acid with the parent polymer [212]. Reactive metallo mesogens of the structure... 

The most rigid chains are those of ladder polyorganosilsesquioxanes. Together with esters of cellulose, these polymers are an example of the lyotropic liquid crystalline system which is formed by semirigid macromolecules. ITie structure of their solid mesophasese has not been studied sufficiently enough, therefore, at present it is not clear whether it can be considered as a disordered crystal or as a liquid crystalline phase. Further study of the structure of the mesophases in element-organic polymers and low molecular substances would undoubtedly be very useful for the development of the concept of disordered crystals. 

The second group of systems exhibits the liquid-crystalline state only in the presence of a low-molecular-weight liquid (water, for example). These are really lyotropic liquid-crystalline systems in which self-ordering is caused by their amphiphilic character, i.e., the presence of lyophobic and lyophilic groups at the ends of the long molecules. Soaps, lipids, and some types of proteins are members of this group. The specific features of the phase transitions in them will not be examined here. 

It would thus be fcwmally possible to assign the described system, which contains a liquid-crystalline phase, to lyotropic liquid crystals. Actually, this system differs fiom true lyotropic liquid-crystalline systems with respect to the mechanism of the onset of the ordoed state since only a decrease in the temperature of the C-LC transition is involved in the rigid-chain polymer-solvent system due to addition of the solvent, and in this sense, the system does not differ from thomotropic liquid-crystalline systems formed in the pure polym with an increase in the temperature. In addition, let us examine the behavior of a system with a fixed concentration of solvent cwresponding to a composition of the system V2 (ho% and below, subscripts 1 and 2 in the volume and weight compositimis of the system refer to the solvent and polymer, respectively). An increase in the temperature to Tj results in the complete transition of the system into the liquid-crystalline state, which corresponds to the usual thermotropic transition, and the solvent does not play any specific role here except for decreasing the melting point of the crystalline phase. With a further increase in the tempaature, the same ttansitions LC -> LC +1 (at and LC +1 -> I (at as in ordinary thermotropic liquid-crystalline systems take place. 

The analysis of the properties of lyotropic liquid-crystalline systems in concentrated solutions of ladder polyorganosilsesquioxanes [23-25,29], in parti-... 

Lyotropic Liquid-Crystalline Systems Based on Polypeptides... 

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