Lyotropic liquid crystals normal structures

The lyotropic liquid crystals have been studied as a separate category of liquid crystals since they are mostly composed of amphiphilic molecules and water. The lyotropic liquid-crystal structures exhibit the characteristic phase sequence from normal micellar cubic (IJ to normal hexagonal (Hi), normal bicontinuous cubic (Vi), lamellar (1 ), reverse bicontinuous cubic (V2), reverse hexagonal (H2), and reverse micellar cubic (I2). These phase transitions can occur, for instance, when increasing the apolar volume fraction [9], or decreasing the polar volume fraction of the amphiphilic molecule, for example, poly(oxyethylene) chain length in nonionic poly(oxyethylene) alkyl (oleyl) or cholesteryl ether-based systems (10, 11). 

Structurally, the cubic lyotropic liquid crystal phases are not as well-characterised as the lamellar or hexagonal phases. However, two types of cnbic lyotropic liquid crystal phases have been estabhshed and each can be generated in the normal manner (water continuous) or in the reversed manner (non-polar chain continnous), which makes for a total of fottr different phase types. The most well-known cnbic phase consists of a cubic arrangement of molecular aggregates. The molecttlar aggregates are similar to micelles (Ij phase) or reversed micelles (1 phase). The stractrrre of the normal (1 ) cubic... 

The nature of the lyotropic liquid crystal phase formed by amphiphiles in solution is described at a molecular level by the surfactant packing parameter model, introduced in Section 4.9. Consider the situation where the head group has a larger effective cross-sectional area than the chain. This is the usual situation, and the resulting structures are termed normal structures. If there is a large difference in cross-sectional area between the head group and chain (Ns < ), spherical micelles are formed (Fig. 4.24a). For molecules with less of a mismatch between the effective head and tail cross-sectional areas, rod-like micelles provide a more... 

Most mesogenic salts derived from aliphatic acids, (R-COO) M (R = alkyl (normal and branched) or alkenyl M=Li, Na, K, Rb, Cs, NH4, Tl, Pb or other metal) form layered structures (lamellar phases, neat phases) that are similar to smectic A phases. However, mesogenic salts form double layers and are not miscible with smectic A phases [276]. Some of the materials show very complicated polymorphism with a large number of mesophases [276-279]. In general, the transition temperatures of the salts are quite high compared with those of nonpolar liquid crystals. Most of the salts can also form lyotropic liquid crystals. 

X-ray measurements normally give information on the structure of the system studied. In special cases however, such as the lyotropic and the thermotropic smectic-A phases of liquid crystals or two dimensional solids, thermodynamic properties can be obtained reliably from the analysis of the shape of the structure factor. 

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