Reverse hexagonal

Bicontinuous cubic phase Lamellar phase Bicontinuous cubic phase Reverse hexagonal columnar phase Inverse cubic phase (inverse micellar phase)... 

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

When layers of certain block copolymers of ethylene oxide and butylene oxide are contacted with water, there is an initial period when the position of the interface is proportional to tm, where m < 0.5 [32]. That is, initial swelling is not controlled by diffusion but instead by hydration and rearrangement of the long molecules to form the various phases. In the case of (EO)i6(BO)22 small-angle X-ray scattering did detect evidence of both reverse hexagonal and lamellar phases during this initial period, but it was not clear whether all the swollen block copolymer layer consisted of these phases or how the... 

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... 

Fig. 1. Factors involved in the intramitochondrial transport of cholesterol. Left, membrane fusion stimulating reversed hexagonal phase formation right, permeation of cholesterol across membranes (from Ref. 25, with permission).

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. 

H2O Micelle (Lj) < Hexagonal (Hj) < Lamellar (Lq) < Reversed Hexagonal (H2) < Reversed Micelle (L2) Solid... 

Typical surfactant-water-phase diagrams are shown in Fig. 3.4 for single-chained ionic, and non-ionic surfactants respectively. Below a "Krafft" temperature characteristic of each surfactant, the chains are crystalline and the surfactant precipitates as a solid. Increased surfactant concentration (Fig. 3.4) results in sharp phase boundaries between micellar rod-shaped (hexagonal), bilayer (lamellar) and reversed hexagonal and reversed micellar phases. (The "cubic" phases, bicontinuous, will be ignored in this section and dealt with in Chapters 4,5 and 7.)... 

Figure 4.11 Plot of the approximate compositions for which surfactant/water mixtures can form monolayers versus the surfactant parameter of the surfactant. This plot is for chain lengths of 14A, which corresponds to hydrocarbons made up of about 12 carbon atoms. The notation for various mesophases is as follows Vi, V2 are bicontinuous cubic phases (the former containing two interpenetrating hydrophobic diain networks in a polar continuum, the latter polar networks in a hydrophobic continuum). Hi and H2 denote normal and reversed hexagonal phases. La denotes the lamellar phase, and Li and L2 denote isotropic micellar and reversed micellar phases (made up of spherical micelles).

The effect of temperature on double-chain zwitterionic surfactants and uncharged lipids is to increase v/al further beyond unity, allowing a range of aggregation states. For example, the diacyl lipid didodecyl phosphatidylethanolamine mixed with about 20% water exhibits "lamellar", cubic (V2) and reversed hexagonal (H2) phases upon heating [15]. This... 

Recent studies by Lin and co-workers [63] have shown that not only the fatty acid composition influences the kind and ratio of carbonyls formed during heating of lipids, but also the structure of the reaction medium. The type of self-assembly stmcture had a significant influence on reaction yields. Egg phosphatidylcholin, which forms a lamellar phase together with water, generated significantly more 41 than phosphatidylethanolamine which adopts a different nanostructure, namely a reversed hexagonal structure. 

If the third component is a water-insoluble alcohol (five carbons or more), amine, carboxylic acid, or amide, the phase topography is profoundly modified. The phase diagram shown in Figure 3.8b [7] shows in addition to LI and HI a very large lamellar phase, a narrow reverse hexagonal phase H2, and, even more important, a sector-like area of reverse micelles L2. This means that the solubility of n-decanol in a sodium octanoate-water mixture containing between 25 and 62% amphiphile is far more important (30 to 36%) than pure water (4%) and pure sodium octanoate (almost zero). This phase is essential to obtain water-in-oil (w/o) microemulsions. 

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. 

FIG. 2 Laccase catalytic activity in different phases (reverse micellar—L2, lamellar—D, and reverse hexagonal—F) of the ternary diagram for the AOT-water-octane system presented in Fig. 1. (From Ref. 2.) The a and b catalytic profiles were measured in the ternary mixtures corresponding to some cross-sections of a and type, respectively (Fig. 1). The dashed line shows the catal5dic activity of laccase in aqueous solution. 

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... 

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