Amphiphilic mesophases cubic

The cubic amphiphilic mesophases (Sic, Vi, and V2) from their interposition in the succession of mesophases Sic, Mi, Vi, G, V2, and M2, have generally been termed liquid crystalline like the optically anisotropic amphiphilic mesophases Mi, G, and M2. The cubic mesophases formed by non-amphiphilic globular molecules have however usually been termed plastic crystals. This nomenclature has obscured the fact that these plastic crystals are fundamentally liquid crystals rather than solid cyrstals and bear a relationship to the optically anisotropic non-amphiphilic smectic and nematic liquid crystals similar to that born by the amphiphilic cubic mesophases to the optically anisotropic neat (G) and middle (Mi and M2) liquid crystalline phases. 

Amphiphilic Cubic Mesophases Viscous Isotropic Phases. In Figure 1, at positions where a high concentration of globular micellar forms might be expected, the cubic viscous isotropic mesophases Sic, Vi, and V2 are encountered. This is further illustrated by Figure 5. These mesophases, because of their inclusion within the general sequence of amphiphilic mesophases ... 

Figure 5. Formation of the hexagonal, lamellar, and cubic amphiphilic mesophases by the interactions between fibrous, lamellar, and globular micelles,...

Gray, G.W. and Winsor, P.A. (1976) Generic relationships between non-amphiphilic and amphiphilic mesophases of fused type. Relationship of cubic mesophases (plastic crystals) formed by non-amphiphilic globular molecules to cubic phases of amphiphilic series. Adv. Chem. Ser., 152, 1-12. 

The distribution of defects in mesophases is often regular, owing to their fluidity, and this introduces pattern repeats. For instance, square polygonal fields are frequent in smectics and cholesteric liquids. Such repeats occur on different scales - at the level of structural units or even at the molecular level. Several types of amphiphilic mesophase can be considered as made of defects . In many examples the defect enters the architecture of a unit cell in a three-dimensional array and the mesophase forms a crystal of defects [119]. Such a situation is found in certain cubic phases in water-lipid systems [120] and in blue phases [121] (see Chap. XII of Vol. 2 of this Handbook). Several blue phases have been modeled as being cubic centred lattices of disclinations in a cholesteric matrix . Mobius disclinations are assumed to join in groups of 4x4 or 8x8, but in nematics or in large-pitch cholesterics such junctions between thin threads are unstable and correspond to brief steps in recombinations. An isotropic droplet or a Ginsburg decrease to zero of the order parameter probably stabilizes these junctions in blue phases. 

At higher concentrations, micelles assemble in turn, to form hexagonal or cubic phases while longer chains or multi-chain compounds afford lamellar phases in which the amphiphilic derivative is arranged in parallel bilayers, separated by water. The succession of mesophases depending on temperature and concentration of the amphiphile can be visualized in a phase diagram (Fig. 3 c). 

Winsor, P. A. Non-amphiphilic cubic mesophases plastic crystals . Chapter 2.2 in Ref. 15b... 

Relationship of Cubic Mesophases ("Plastic Crystals ) Formed by Non-Amphiphilic Globular Molecules to Cubic Mesophases of the Amphiphilic Series... 

Non-Amphiphilic Cubic Mesophases Plastic Crystals. The cubic plastic crystals of the non-amphiphilic series, to which the amphiphilic... 

Table II. Crystalline Forms of Some Non-Amphiphilic Plastic Crystals (23,24) and of Some Amphiphilic Cubic Mesophases...

One feature of the non-amphiphilic cubic mesophases is that they frequently show mutual miscibility even when constituted from dissimilar molecules. Such miscibility, which contrasts with the immiscibility between dissimilarly constituted solid crystals, is also found between nematic mesophases, between corresponding smectic polymorphs, and, of course, between amorphous liquids. This miscibility is important in its implication that in the cubic mesophases of the amphiphilic series there could well be an equilibrium of related globular micellar forms (Figures 1 and 5) rather than a single clearly defined form. 

An important characteristic of the cubic mesophases, either non-amphiphilic or amphiphilic, is that because of the fairly free thermal rotational motions of their constituent units, they typically give high resolution NMR spectra. In this respect they behave like amorphous liquids and quite differently from conventional solids or from mesophases such as Mi, M2, or G in which rotation of the units is more severely restricted. 

Formation of the Vi and V2 Mesophases and of the Non-Amphiphilic Cubic Mesophase "Smectic D . In Figures 1 and 5, the formation of the amphiphilic cubic mesophases Vi and V2 is attributed to transitional globular micellar forms which arise intermediate between the indefinitely extended fibrous (M) and lamellar (G) forms which constitute the middle and neat mesophases, respectively. With a few non-amphiphilic mesogens (19, 20, 21, 22) a cubic mesophase "smectic D is found intermediate in the thermal succession of mesophases between smectic A... 

Amphiphilic lipopeptides with a hydrophobic paraffinic chain containing from 12 to 18 carbon atoms and a hydrophilic peptidic chain exhibit lyotropic meso-phases and good emulsifying properties. The X-ray diffraction study of the mesophases and of dry lipopeptides showed the existence of three types of mesomorphic structures lamellar, cylindrical hexagonal and body-centred cubic. Two types of polymorphism were also identified one as a function of the length of the peptidic chain and the other as a function of the water content of the mesophases. The emulsifying properties of the lipopeptides in numerous pairs of immiscible liquids such as water/ hydrocarbons and water/base products of the cosmetic industry showed that small amounts of lipopeptides easily give three types of emulsions simple emulsions, miniemulsions and microemulsions. 

Structure and Polymorphism of Lipopeptides. Amphiphilic lipopep-tldes Cjj(AA)p exhibit mesophases in aqueous solution for water concentrations smaller than about 60 %, The structure of the mesophases and of the dry lipopeptides obtained by evaporation of the mesophase water at a slow rate was determined by X-ray diffraction. Lipopeptides X-ray diagrams obtained are similar to those exhibited by classical amphiphiles (11). They have allowed us to establish the existence of three types of liquid-crystalline structures Isunel-lar, hexagonal and cubic. 

Bull, T. and Lindman, B. (1975) Amphiphile diffusion in cubic lyotropic mesophases. Mol. Cryst. Liquid Cryst., 28, 155-160. 

Figure 3. Sketch of the principal phase behavior of amphiphilic compounds. Usual amphiphiles are represented by a vertical line in this scheme they exhibit only one type of mesophase. Extreme geometries of one of their molecular parts or the addition of solvents (linear alkanes or water) may lead to a deviation from the vertical orientation of that line, thus, amphiphilic compounds in such situations may form various types of liquid crystal phases T = temperature, SmB phase (rotator phase), Cubjn and Cub(,i = cubic discontinuous or cubic bicontinu-ous phases, respectively, Col, i = columnar hexagonal phase, Iso = isotropic phase.

The lyotropic behavior of these carbohydrate derivatives has been studied very carefully [96]. It follows the classical sequence of mesophases established for the ionic detergents such as soaps. In contact preparations of l-0-octyl-/3-D-glucopyranoside (10 e) with water at room temperature three types of lyomesophases are observed (from high to low amphiphile concentration) lamellar, cubic and columnar hexagonal, their principal structures are depicted in Fig. 12. 

Other types of interesting, sometimes even curious, amphotropic materials with unusual molecular architectures have also been found. Whereas T-shaped [109] molecular structures have flexible wings, T-shaped compounds are made of rigid lipophilic units [166]. In the T-shaped case, smectic instead of columnar phases are observed. While mono-alkylated amphiphiles usually show only SmA phases, an interesting exception are so-called banana shaped amphiphiles of which 51 in Fig. 35 may be an example. This gentiobioside exhibits a bi-continuous cubic mesophase [129]. 

In the (EO)i7(BO),o/D20/p-xylene Alex-andridis et al. claimed the first, to their knowledge, reverse micellar cubic phase in a typical ternary amphiphile/water/oil system [143] before studying and reporting the system in more detail [144]. They report six mesophases and two solution phases at 25 °C. On increasing the polymer concentration along the polymer-water axis the phase sequence Lj (<22% polymer), I, (23-37%), Hi (42-54%), L (62-84%) is... 

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