Lyotropic liquid

Both polymer melts and polymer solutions sometimes form phases with orientational and positional ordci. Thermotropic polymer liquid crystals possess at least one liquid crystal phase between the glass-transition temperature and the transition temperature to the isotropic liquid. Lyotropic polymer liquid crystals possess at least one liquid cry stal phase for certain ranges of concentration and temperature. 

The structure of the lyotropically mesomorphous lattice is made up of multimolecular units called mesoaggregates. These are surrounded by an intervening liquid. Lyotropic mesomorphism is therefore closely related to the tendency of lipids to accumulate at interfaces. The surface activity is a consequence of the same dualistic polar/non-polar molecular structure that causes the formation of micelles in solutions of association colloids (I, 2, 3, 4, 5, 6). 

Lyotropic liquid crystals are discussed in section C2.3 and section C2.6 of tliis encyclopedia and will not be considered furtlier here. 

Alexandridis P, Olsson U and Lindman B 1997 Structural polymorphism of amphiphilic copolymers Six lyotropic liquid crystalline and two solution phases in a poly(oxybutylene)-poly(oxyethylene)-water-xylene system Langmuir 23-34... 

Lyophobic colloids Lyotropic liquid crystals Lyotropic mesophases Lyotropic polymers Lyral [31906-04-4]... 

Liquid crystals may be divided into two broad categories, thermotropic and lyotropic, according to the principal means of breaking down the complete order of the soHd state. Thermotropic Hquid crystals result from the melting of mesogenic soHds due to an increase in temperature. Both pure substances and mixtures form thermotropic Hquid crystals. In order for a mixture to be a thermotropic Hquid crystal, the different components must be completely miscible. Table 1 contains a few examples of the many Hquid crystal forming compounds (2). Much more is known about calamitic (rod-Hke) Hquid crystals then discotic (disk-like) Hquid crystals, since the latter were discovered only recendy. Therefore, most of this section deals exclusively with calamities, with brief coverage of discotics at the end. 

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

T. K. Attwood, J. E. Lydon, C. Hall, G. L. Tiddy. The distinction between chromonic and amphiphilic lyotropic mesophases. Liquid Cryst 7 657-668,1990. 

Khoklov, A. R. and Grosberg, A. Yu. Statistical Theory of Polymeric Lyotropic Liquid Crystals. Vol. 41, pp. 53-97. 

Like other surfactants, alkanesulfonates generate lyotropic liquid-crystalline phases. But the phase equilibria can only be inadequately described because of the enormous experimental difficulties in, for instance, establishing an appropriate equilibrium. Nevertheless, for simple ternary systems the modeling of surfactant-containing liquid-liquid equilibria has been successfully demonstrated [60],... 

Goltner-Spickermann C (2003) Nanocasting of Lyotropic Liquid Crystal Phases for Metals and Ceramics. 226 29-54 Gouzy M-F, see Li G (2002) 218 133-158... 

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... 

Figure 2a shows a schematic phase diagram for lyotropic liquid crystals. This figure shows the formation of micelles, cubic phases, bicontinuous cubic phases, and lamellar phases as the concentration of surfactant increases. Also shown in this figure is a schematic diagram of an ordered bicontinuous cubic phase (Fig. 2b). Another interesting example in...

Firouzi, A Atef, F Oerth, AG Stucky, GD Chmelka, BE, Alkaline Lyotropic Silicate-Surfactant Liquid Crystals, Journal of the American Chemical Society 119, 3596, 1997. 

Rill, RL Locke, BR Liu, Y Van Winkle, DH, Electrophoresis in Lyotropic Polymer Liquid Crystals, Proceedings of the National Academy of Science, USA 95, 1534, 1998. 

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... 

Similar behavior can occur when a crystalline network is disassembled by adding a solvent rather than by heating. These mesogens are called lyotropic liquid crystals and the mesophase formation shows temperature and concentration dependence. They are very important in biological systems, but have been much less studied in materials science. 

Figure 8.4 (a) Atypical molecule that behaves as lyotropic liquid crystal (b) schematic representation of a plate-shaped micelle (c) a spherical micelle (d) a cylindrical micelle. 

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

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