Lyotropic liquid-crystalline ordering

Lyotropic liquid-crystalline ordering was also observed for cylindrical brushes formed by the homopolymerization of macromonomers, i.e. macromolecules with polymerizable endgroups (Figure 34) [403]. The extended conformation of these cylindrical brushes is controlled by the coiling and steric repulsion of the side chains and is independent of the unperturbed flexibility of the backbone segments [402]. 

The exploitation of lyotropic liquid crystalline order by Kwolek" to process Kevlar fibres established a principle—but one which was retained in the hands of specialized fibre producers. The extension from lyotropic to thermotropic polymers by Jackson and Kuhfuss opened the field to conventional thermoplastics processing. The variability of thermoplastics processing technology takes one into products of complex shapes and more complex flow histories and so an even greater interdependence between flow history, morphology and properties. 

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. 

Note 2 A liquid-crystalline polymer can exhibit one or more liquid state(s) with one- or two-dimensional, long-range orientational order over certain ranges of temperatures either in the melt (thermotropic liquid-crystalline polymer) or in solution (lyotropic liquid-crystalline polymer). 

Liquid crystals are classified into lyotropic and thermotropic crystals depending on the way in which the mesomorphic phase is generated. Lyotropic liquid-crystalline solvents are formed by addition of controlled amounts of polar solvents to certain amphiphilic compounds. Thermotropic liquid-crystalline solvents, simply obtained by temperature variations, can be further classified into nematic, smectic, and cholesteric solvents depending on the type of molecular order present. Liquid crystals are usually excellent solvents for other organic compounds. Nonmesomorphic solute molecules may be incorporated into liquid-crystalline solvents without destruction of the order prevailing in the liquid-crystalline matrix (Michl and Thulstrup, 1986). Ordered solvent phases such as liquid crystals have also been used as reaction media, particularly for photochemical reactions (Nakano and Hirata, 1982). 

For a summary of lyotropic polypeptide glasses see E. T. Samuels, Liquid crystalline order in polypeptides in A. Blumstein, ed. Liquid Crystalline Order in Polymers . Academic Press, New York, NY 1978. For the description of glasses of dicholesterylesters of dicarboxylic acids see D. Gross, Z, Naturforsch. B27, 472 (1972)... 

The present knowledge about molecular organization in lyotropic liquid crystalline phases is summarized. Particular attention is given to biologicaly relevant structures in lipid-water systems and to lipid-protein interactions. "New findings are presented on stable phases (gel type) that have ordered lipid layers and high water content. Furthermore, electrical properties of various lipid structures are discussed. A simple model of l/l noise in nerve membranes is presented as an example of interaction between structural and electrical properties of lipids and lipidr-protein complexes. 

It is now generally accepted that folding is universal for spontaneous, free crystallisation of flexible polymer chains. It was first of all found in crystallisation from very dilute solutions, but it is beyond doubt now, that also spherulites, the normal mode of crystallisation from the melt, are aggregates of platelike crystallites with folded chains, pervaded with amorphous material. "Extended chain crystallisation" only occurs under very special conditions in the case of flexible chains for rigid polymer chains it is the natural mode ("rigid rod-crystallisation" from the melt in case of thermotropic polymers, and from solution in case of the lyotropic liquid-crystalline polymers both of them show nematic ordering in the liquid state). 

Hydrophobically modified polybetaines combine the behavior of zwitterions and amphiphilic polymers. Due to the superposition of repulsive hydrophobic and attractive ionic interactions, they favor the formation of self-organized and (micro)phase-separated systems in solution, at interfaces as well as in the bulk phase. Thus, glasses with liquid-crystalline order, lyotropic mesophases, vesicles, monolayers, and micelles are formed. Particular efforts have been dedicated to hydrophobically modified polyphosphobetaines, as they can be considered as polymeric lipids [5,101,225-228]. One can emphasize that much of the research on polymeric phospholipids was not particularly focused on the betaine behavior, but rather on the understanding of the Upid membrane, and on biomimicking. So, often much was learnt about biology and the life sciences, but little on polybetaines as such. 

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. 

In contrast to polypeptides that have many possible conformations, poly(hexyl isocynate) is known to have a stiff rodlike helical conformation in the solid state and in a wide range of solvents, which is responsible for the formation of a nematic liquid crystalline phase.45-47 The inherent chain stiffness of this polymer is primarily determined by chemical structure rather than by intramolecular hydrogen bonding. This results in a greater stability in the stiff rodlike characteristics in the solution as compared to polypeptides. The lyotropic liquid crystalline behavior in a number of different solvents was extensively studied by Aharoni et al.48-50 In contrast to homopolymers, interesting new supramolecular structures can be expected if a flexible block is connected to the rigid polyisocyanate block (rod—coil copolymers) because the molecule imparts both microphase separation characteristics of the blocks and a tendency of rod segments to form anisotropic order. 

A variable-director NMR method was used to investigate the order and dynamics of aromatic polyamides in lyotropic liquid crystalline phases. " In... 

As their name implies, liquid crystals are materials whose structures and properties are intermediate between those of isotropic liquids and crystalline solids (2). They can be of two primary types. Thermotropic liquid crystalline phases are formed at temperatures intermediate between those at which the crystalline and isotropic liquid phases of a mesogenic compound exist. Substances which exhibit thermotropic phases are generally rod- or disc-like in shape, and contain flexible substituents attached to a relatively rigid molecular core. Lyotropic liquid crystalline phases are formed by amphiphilic molecules (e.g. surfactants) in the presence of small amounts of water or other polar solvent. In general, the constituent molecules in a liquid crystal possess orientational order reminiscent of that found in the crystalline phase, yet retain some degree of the fluidity associated with the isotropic liquid phase. 

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