Cubic phases rheology

The dDAVP preparations used in this study were prepared in low water contents so that the lamellar phase was formed, which in turn was injected into the rabbits. The reason for this was the fact that the lamellar phase with its mucous-like rheology is easier to inject than the stiff cubic phase. Since the lamellar phase swells into the cubic phase in excess water according to the phase diagram in Figure 1, a phase transition was expected also in the in vivo situation. The transition was found to be very fast as judged by inspection of the injection site immediately after administration. 

Portmann, M Landau, E. M., and Luisi, P. L. (1991). Spectroscopic and rheological studies of enzymes in rigid lipidic matrices the case of a-chymotrypsin in a lysolecithin/water cubic phase. J. Phys. Chem., 95, 8437 0. 

Very few rheological data have been reported for ordered cubic phases of surfactant solutions. However, Radiman et al. (1994) have reported dynamic oscillatory data for solutions of didodecyldimethylammonium bromide (DDAB) in deuterated water and octane. Their data for type II cubic P and D phases are shown in Fig. 12-29. They report that the samples... 

M., and Kunieda, H. (2004) Rheology and dynamics of micellar cubic phases and related emulsions. Langmuir, 22, 5235-5240. 

There are a number of liquid crystalline phases formed by amphiphilic molecules, notably surfactants, polar lipids and block copolymers, including discrete and bicontinuous cubic phases, hexagonal phases (and their reversed counterparts), lamellar phases, intermediate phases, etc. A number of these phases are interesting from a drug delivery point of view. This is due to the frequently large solubilization capacity of both hydrophilic and hydrophobic substances, possibilities to control the drug release rate, favourable rheological properties, suitable water transport rates, excellent stability, etc. 

Lyotropic liquid crystal phases has been observed when l-Alkyl-3-methylimidazolium bromide (CnmimBr) was mixed with p-xylene and water. SAXS, POM, NMR and rheology measurements were performed to investigate the lyotropic liquid crystal phases. A lyotropic bicontinuous cubic phase formed in imidazolium-type ionic liquid (IL) system was found for the first time. The strong %-% stacking of imidazolium based ILs and their 71-cation interactions with p-xylene molecules have unique effect on the structural parameters.Description of NMR of quadrupolar systems using the Holstein-Primakoff (HP) formalism and its analogy with a Bose-Einstein condensate (BEC) system has been presented. Two nuclear spin... 

Dynamic rheological measurements show that the cubic phases behave like the viscoelastic vesicle phases, as can be seen from the two examples shown in Figure 10.19. As can be seen, G is independent of the frequency and at least one order of magnitude higher than G", and rj increases to infinity when the frequency approaches zero. However, as can be expected from the stiffness of the samples, both Go and cry are several orders of magnitude higher than for the vesicle phases. As has been found for the latter, the cubic phases have energy elasticity, i.e. the moduli break down at deformations beyond about 10%. 

In this connection, it is interesting that vesicles can also form a cubic phase at high concentrations, if they are very monodisperse. This condition has been found to be fulfilled in a system of sodium oleate/octanol/water at a cosurfactant surfactant ratio of around 3 1 in the water-rich comer however, such cubic phases of vesicles are very rare, because the vesicles are not sufficiently monodisperse in most of the systems. These cubic phases of vesicles have similar rheological properties to the other cubic phases, and the values for Go and Gy are also considerably higher than for the normal vesicle phases. 

It has been found for many cubic phases consisting of spherical particles that the moduli calculated with the hard-sphere model are often in good agreement with the ones determined experimentally. However, it must be stated here that also for the cubic phases a generally valid model for a theoretical description of their rheological behaviour is not available at present (mainly due to the uncertainties in the choice of fi). 

Radiman, S., Toprakcioglu, C. and McLeish, T., Rheological study of ternary cubic phases, Langmuir, 10, 61-67 (1994). 

Solids concentrations can vary from a few percent to well over 50% in a typical stirred tank. Solids concentration, particle shape, and the viscosity of the suspending phase are the main factors affecting the rheology and settling characteristics of the slurry. Cubic- and spherical-shaped solids tend to form Newtonian slurries, while needle-, oblong-, and plate-shaped solids form thixotropic slurries. Such slurries exhibit yield stresses even at quite low solids concentrations. This can lead to the development of caverns, as shown in Section 9.4. Proper design can usually overcome these stagnation problems. 

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