Cubic fluid mesophases

In our most recent work we learned how to prepare discontinuous cubic micellar mesophases (termed Q ) that are very fluid and almost Newtonian. The Ql structures... 

Although the cubic phase is interesting in several regards, it is particularly worth noting that while liquid crystal mesophases are fluid, cubic phases are very viscous. Furthermore, because of their high symmetry, cubic phases possess isotropic physical properties, setting them apart from other liquid-crystal mesophases. Transitions into, and out of, cubic phases tend to be rather slow. Exactly why cubic phases form in calamitic systems is tmclear at the present time. 

At higher temperatures and water concentrations, the system may shift into the cubic mesophase structure (see Figure 15). The water is present as spheres totally surrounded by monoglyceride. This phase has a high viscosity and is sometimes called viscous isotropic in the hterature the two terms refer to the same structure. In the presence of more water than can be accommodated in the internal spherical phase, one obtains a mixture of lumps of this cubic structure dispersed in excess water. With a saturated monoglyceride such as GMS, the lamellar structure is the main mesophase found under practical conditions, while with unsaturated monoglycerides this cubic phase is the predominant one at lower temperatures. At lower water concentrations, the spherical water micelles are farther apart, so the viscosity of the mixture becomes lower, approaching that of melted pure surfactant. This is the fluid isotropic mesophase, sometimes referred to as the L2 phase. 

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 1.92 Structural representations of the main cubic mesophases formed by lipid assemblies. The mesophases shown are (a) Ia3d (Q °) and (b) Pn3m both of which are Qn fluid cubic phases ...

Fig. 12.5 Temperature-composition phase diagram of the monoolein/water system (up to 50 wt% water). A cartoon representation of the various phase states is included in which colored zones represent water. The mesophases are as follows Lc-crystalline lamellar, La-lamellar, la3d-gyroid inverted bicontinuous cubic, Pn3m-primitive inverted bicontinuous cubic, Hn-inverted hexagonal, and Fl-reverse micelles fluid phases (Taken from [8])...

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