Liquid reverse hexagonal

L micellar solution phase L lamellar liquid crystalline phase V viscous isotropic phase H2 reverse hexagonal phase... 

Solyom and Ekwall (20) have studied rheology of the various pure liquid crystalline phases in the sodium caprylate-decanol-water system at 20 °C, for which a detailed phase diagram is available. Their experiments using a cone-and-plate viscometer show that, in general, apparent viscosity decreases with increasing shear rate (pseudo-plastic behavior). Values of apparent viscosity were a few poise for the lamellar phase (platelike micelles alternating with thin water layers), 10-20 poise for the reverse hexagonal phase (parallel cylindrical micelles with polar... 

FIGURE 21.6 Ternary phase diagram of the sodium octanoate-decanol-water system at 25°C. There are two isotropic solution phases, micellar and reversed micellar (rev mic), and three liquid crystalline phases, hexagonal (hex), lamellar (lam), and reversed hexagonal (rev hex) (from Ref. 17). 

On the other hand, studies with three-dimensional isotropic lamellar matrices have shown that Azone is a weakly polar molecule, which can occupy the interfacial region as well as the hydrocarbon interior of bilayers [86,87]. The contrasting observations of Azone promoting the assembly of reversed-type liquid-crystal phases (e.g., reversed hexagonal and reversed micellar) in simple model lipid systems [88-90], while also favoring the formation of lamellar structures in one of these mixtures [91], adds further confusion to the discussion [92]. This notwithstanding, the studies by Schiickler and co-workers [91] emphasize the differences in the calorimetric profiles of intact human stratum comeum (HSC) and model SC lipid mixtures Although these systems are clearly useful and versatile, extrapolation of inferences from model lipids to the intact membrane must be performed with caution. 

Lyotropic liquid crystalline phase with reverse hexagonal stmcture... 

FIG. 1 Phase diagram for Aerosol OT (AOT)-water-octane system. The boundaries of each individual phase were determined with 50 mM phosphate + 50 mM acetate buffer as an aqueous component (—). (From Ref. 2.) LI, L2 normal and reverse micelles of surfactant, respectively D, F liquid crystalline mesophases with lamellar and reverse hexagonal packing of surfactant molecules, respectively. Concentrations of all components are expressed as %(w/w). Cross-section of a type shows an example of the variation of water content at constant surfactant-to-organic solvent ratio cross-section of p type shows an example of the variation of organic solvent content at constant water-to-surfactant molar ratio. 

Alfredsson V, Andersson M, KjeUin P, Pabnqvist AEC. 2002. Macroscopic alignment of silver nanoparticles in reverse hexagonal liquid crystaUine templates. Nano Lett 2 1403-1407. 

Huang LM, Mitra AP, Wang HT, Wang ZB, Van YH, Zhao D. 2002. Cuprite nanowires by electrodeposition from lyotropic reverse hexagonal liquid crystalline phase. Chem Mater... 

Figure 1 A phase diagram of a system composed oflipids extracted from cereal lipids and water. The weight fraction of each component is given in the diagram. L3, sponge phase LC, liquid crystal LC-L, lamellar liquid crystal and LC-H, reverse hexagonal liquid crystal.

Figure 4 A phase diagram of a system composed of monoolein and water. One representative structure of a bicontinuous cubic liquid crystalline phase is shown to the right. L, lamellar liquid crystal Hn, reverse hexagonal liquid crystal and Li, reverse micellar phase.

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). 

In an additional study by Yuli-Amar et al., in order to achieve low-viscosity reverse hexagonal phases at room temperature, ethanol and diethylene glycol monoethyl ether (Transcutol) were added to the ternary GMO/TAG/water mixture [29], These studies were based on findings showing that alcohols can destroy liquid-crystal phases, and ethanol and PEG were shown to form discontinuous micellar cubic and sponge phases instead of bicontinuous phases (49-51). It was shown that the addition of Transcutol or ethanol to the GMO/TAG/water mixture enabled the formation of a room temperature fluid Hn phase. 

Figure 11.12 shows the proposed scheme for the stractural evolution during the synthesis, based in a liquid-crystal templating (LCT) mechanism. Initially, the aqueous acid solution is solubihzed in the cyhndrical reverse micelles forming the reverse hexagonal phase. Nonhydrolyzed TEOS molecules and PDMS chains are mutually soluble and therefore constitute the hydrophobic continuous medium. The hydrolysis is probably driven by interfacial diffusion of the water towards the... 

Amar-Yuli et al. combined the potential of both liquid crystalline structure as well as glycerol as cosolvent to enhance insulin thermal stability and moderate the aggregation progress [49]. Insulin was incorporated into several modified reverse hexagonal systems based on friendly surfactant and polyols to explore the impact of the protein confinement on its stability, unfolding behavior, and morphology with severe external conditions, low pH, and higher temperatures (up to 70 °C). 

Liquid crystalline phases, such as lamellar, reverse hexagonal, and cubic, present interesting properties for a topical delivery system, and hence were considered and have been smdied as delivery vehicles of pharmaceuticals via the skin and mucosa... 

D. Libster, P. Ben Ishai, A. Aserin, G. Shoham, N. Garti, Prom the microscopic to the mesoscopic properties of lyotropic reverse hexagonal liquid crystals. Eangmuir 24, 2118-2127 (2008)... 

D. Libster, A. Aserin, N. Garti, Interactions of biomacromolecules with reverse hexagonal liquid crystals drug delivery and crystallization applications. J. Colloid Interf. Sci. 356, 375-386 (2011)... 

As an example of the effects of an amphiphilic drug on the structure of surfactant self-assemblies. Figure 1.4 shows part of the phase diagram of monoolein, water, lidocaine base and licocaine-HCl (21). As can be seen, the cubic phase (c) formed by the monoolein-water system transforms into a lamellar liquid crystalline phase on addition of lidocaine-HCl, whereas it transforms into a reversed hexagonal or reversed micellar phase on addition of the lidocaine base. Based on X-ray data, it was inferred that the cubic phase of the monoolein-water system had a slightly reversed curvature (critical packing parameter about 1.2). Thus, on addition of the... 

Many different structures Liquid crystalline phases Lamellar Hexagonal Reversed hexagonal... 

Figure 7.4. Structure of the reversed hexagonal lyotropic liquid crystal phase.

Rgure 16 Schemes for the self-assemblies of an amphiphilic diblock copolymer in the presence of the solvents water and oil selective for the two blocks, (a) Micellar solution, (b) micellar cubic lyotropic liquid crystal (LLC), (c) hexagonal LLC, (d) lamellar LLC, (e) reverse hexagonal LLC, (f) reverse cubic LLC, (g) reverse micellar solution. (From P. Alexandridis et al. Langmuir 13 23, 1997, Copyright 1997 American Chemical Society.)... 

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