Inverse cubic phases

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

Fig. 4.44 Phase diagram for aqueous solutions of Pluronic P104 (PEOi7PP05,PFX)27) (Noolandi et al. 1996). Notation iso, isotropic (polymer poor) solution cubic, cubic phase hex[, hexagonal phase lam, lamellar phase, hex2, inverse hexagonal phase, cubicj, inverse cubic phase, iso2, isotropic (polymer rich) solution. The solid and dashed lines are calculated from the continuum and lattice versions of self-consistent field theory respectively.

The aggregation behavior of AB silicone surfactants in nonpolar oils including several hydrocarbon oils has been reported by Rodriguez [46]. They found that inverse micelles were formed in all oils, adjacent to the inverse cubic phase formed by the neat copolymers and by concentrated mixtures of copolymer and oil. The CMC depended strongly on the length of the pEO chain but only weakly on the pDMS chain. Inverse hexagonal phase was also observed. 

Lyotropic mesophases usually formed from such substances are beside the lamellar phase the inverse hexagonal and different types of inverse cubic phases. Nanoparticles based on lamellar structures ((multilamellar) vesicles, liposomes) will not be... 

In addition to the cubic and/or inverse cubic forms described above, further transitional forms exist between the lamellar phase and the hexagonal mesophase (cubic, type II) or inverse hexagonal mesophase (cubic, type III) [6]. In contrast to the discontinuous phases of types I and IV, cubic mesophases of type II and III belong to the bieontinuous phases (Fig. 4f). A range of lyotropic mesophases are possible, depending on the mesogen concentration, the lipophilic or hydrophilic characteristics of the solvent, and the molecule itself [6]. 

Many single-chain amphiphiles form cubic phases when added to water in a given composition. Two of the most well known are didodecyl-phosphatidyl ethanolamine, and mono-olein. Figure 9.18 shows some idealized bicontinous cubic structures of the former, including typical inverse ones. This is also highly viscous and optically transparent as are most of the other cubic phases. 

The phase behaviour established for concentrated aqueous solutions of PEO-PPO-PEO copolymers has its counterpart in PEO/PBO copolymer solutions. A phase diagram for PE058PB0i7PE0M based on tube inversion experiments is shown in Fig. 4.14 (Luo et al. 1992). The hard gel is isotropic under the polarizing microscope and can be characterized as a cubic phase formed from spherical micelles of a similar size to those in the dilute micellar solution. 

Templer RH, Seddon JM, Duesing PM et al (1998) Modeling the phase behavior of the inverse hexagonal and inverse bicontinuous cubic phases in 2 1 fatty acid phosphatidylcholine mixtures. J Phys Chem B 102 7262-7271... 

Delacroix, H., Gulik-Krzywicki, T., and Seddon, J.M. (1996). Freeze fracture electronmicro-scopy of lyotropic lipid systems quantitative analysis of the inverse micellar cubic phase of space group Fd3m (Q227). J. Mol. Biol. 258, 88-103. 

Cubic strut phases are common in the phase diagrams of two-tailed surfactants. These surfactants have a relatively high value of the vfaolc parameter, because the volume-to-length ratio v/i(. of the double tail is twice that of a single tail. A high value of v/aoic is consistent with the formation of type II bicontinuous and other inverse phases, such as the inverse hexagonal phase in Fig. 12-24. 

Fig. 4. Schematic drawing of lipid-water mesophases (Lc, lamellar crystalline Lps Pp., lamellar gel L , lamellar liquid-crystalline Qn, Qn°, Qn , inverse bicontinuous cubics Hu, inverse hexagonal). The cubic phases are represented by the G, D, and P minimal surfaces, which locate the midplanes of fluid hpid bilayers.

Figure 2 Phase diagram of a binary amphiphile-water mixture obtained from a Ginzburg- Landau model with a vector order parameter for the amphiphile orientation (50,51]. The phases L and L2 are micellar liquids, is a lamellar phase. H and H denote hexagonal and inverse hexagonal phases, respectively, I is an fee crystal of spherical micelles, and V is a simple cubic bicontinuous phase. (From Ref. 51.)...

Lyotropic cubic phases have been the subject of many structural studies [138,157-159]. Their structure is more complicated and less readily visualized than that of other phases. Almost all 3D fluid phases so far observed are of cubic symmetry, although rhombohedral, tetragonal, and orthorhombic phases of inverse topology have been detected in a few systems (based, for example, on SDS or lipids) [160]. There are two distinct classes of cubic phases [110] ... 

A cubic phase of space group laid (which was the first cubic structure to be solved [161] and is among the most commonly observed [162]). The structure of laid belongs to a body-centered space group of rods (which are essentially a surfactant bilayer with a circular cross section) connected 3 x 3 to generate two interwoven but unconnected 3D networks [162]. A chiral cubic phase of space group PA Il has been observed so far in only one lipid-protein-water system [163]. Its proposed structure is similar to that of laid. It has one water-lipid network interwoven with one network of quasi-spherical inverse micelles that encloses the protein molecules. 

A cubic phase of space group Fdim is usually observed in type II systems based on a variety of hydrated lipid mixtures [163,166]. A type I Fdim phase with a very large lattice parameter has been claimed to form in a brine-butanol-SDS-toluene system [167]. The unit cell of the Fdim phase contains two quasi-spherical, differently sized types of inverse micelles [160]. There are eight of the larger and 16 of the smaller micelles per unit cell. 

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