Reverse micellar cubic phase

In the (EO)i7(BO),o/D20/p-xylene Alex-andridis et al. claimed the first, to their knowledge, reverse micellar cubic phase in a typical ternary amphiphile/water/oil system [143] before studying and reporting the system in more detail [144]. They report six mesophases and two solution phases at 25 °C. On increasing the polymer concentration along the polymer-water axis the phase sequence Lj (<22% polymer), I, (23-37%), Hi (42-54%), L (62-84%) is... 

Watanabe, K., Kanei, N., and Kunieda, H. (2002) Highly Concentrated emulsions based on the reverse-micellar-cubic phase. J. Oko Sd., 50, 771-779. 

Fig. 52 Schematic illustration of different modes of self-organization of PE- -PPO- -PEO triblock terpolymer in water. PE segments, A PPO segments, o PEO segments. Ordered phases are denoted as follows a normal (water-continuous) hexagonal. Hi, b lamellar, L, c reverse (polymer-continuous) hexagonal, H2 and d reverse micellar cubic, I2. From [164]. Copyright 2003 EDP Sciences, Societa Italiana di Fisica, Springer...

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). 

Fig. 1 Phase diagram of water/POE(5) system as a function of temperature. Wm aqueous micellar solution phase, Om reverse micellar solution phase, L lamellar liquid crystalline phase, V2 reverse bicontinuous cubic phase, Djt isotropic bicontinuous phase, W excess water phase, S sohd-present region. The filled circle was determined by SAXS...

The rich lyotropic phase behavior exhibited by membrane lipids is well known. The lyotropic phase behavior of membrane lipids whose structure can be described as diacylglucosylglycerols can be classified as sugar fatty acid esters, and have been studied by Mannock et al. [111]. These types of surfactants often exhibit lamellar phases at low temperature, and a transition to a different inverted nonlamellar mesophase, often reverse hexagonal (Hn) or reverse micellar cubic (Qn) phase. In this particular study acyl chains with different terminus, based on stearic and palmitic acid, were studied. Only the shorter chained derivatives tended to form a Qn phase the remainder formed Hn phases over a range of temperatures above 70 °C. 

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

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).

Recently membrane lipids from Brassica napus root cells were examined with respect to effects from dehydration-acclimatised plants [59]. It was found that the lipids formed a cubic phase with excess water vmder physiological conditions. On heating, this phase transformed directly into a reversed micellar phase. The transition was also foxmd to coincide with the temperature limit of survival of the plant. Also after repeated water-deficient stress, a cubic phase is formed in excess water, although there are differences in the phase properties compared to lipids from membranes of plants grown normally. 

Similarly, lyotropic phases may be further subdivided into nematic (N), lamellar (L), micellar cubic (I), bicontinuous cubic (V) and hexagonal (H), with the cubic and hexagonal phases being further classified as normal (oil-in-water, e. g. Vj) or reversed (water-in-oil, e. g. V2). 

The basic mode of mesophase formation is as described above for CTAB. However, as one might expect, things are not quite so straightforward and there are various types of mesophase which can be formed from various types of surfactant. The surfactant structure can be varied so that fluorocarbon chains can be employed in place of the hydrocarbon variety, while anionic (e. g. -SOa") and the neutral (e.g. -(0CH2CH2) -0H) polar headgroups are often used. These surfactants can then form a variety of different mesophases as a function of (mainly) concentration in the solvent of choice (normally water). These phases are the lamellar (L ) phase, a simple bilayer phase, and variations on the cubic (li, I2, Vi, V2) and hexagonal (H, H2) phases. For these last phases, the subscript 1 implied a normal phase as found in a water-rich system, while the subscript 2 implied a reversed phase as found in an oil-rich system. For the cubic phases, the letter F implied a micellar phase (e. g. 

In this diagram, Li is an isotropic solution of micelles, while L2 is a solution of reversed micelles in oil. The phases labelled a-d are all cubic phases as follows a = l2, b = V2, c = Vi and d = li (note that there are no examples known of I2 phases as yet). What the diagram shows is that as the surfactant concentration increases, the surface curvature of the micelles in normal oil-in-water phases gradually reduces, going through zero surface curvature (L phase) and then reverses going into reversed micellar systems. Further, it shows that in principle, one phase is separated... 

Figure 9.8 Micellar structures (A = spherical micelle, B = cylindrical micelle, C = bilayer lamellae, D = reverse micelle, E = biconlinuous cubic phase, F = vesicular-liposomes). (Reproduced with permission from D. F. Evans and H. Wennersttom, eds.. The Colloidal Domain. Where Physics, Chemistry, Biology and Technology Meet. Wiley-VCH, Weinheim, 1984. Cop5fright 1984 Wiley.)...

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.

Figure 4.11 Schematic representation of spherical reverse micellar structure formed in discontinuous cubic (b) phase. The radius of the micelle is r, the radius of the hydrophilic...

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. 

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... 

Figure 1.13, Phase diagram of the monoolein/water system. The cubic phases are denoted G (the gyroid type) and D (the diamond type). The arrows indicate two different means to reach an in situ formation of a bicontinuous cubic phase, i.e. through increasing the temperature of a lamellar phase at a fixed composition (A), and through dilution with water of a reversed micellar phase at a fixed temperature (B) (data from ref. (266))...

Phases built up of discrete aggregates include the normal and reversed micellar solutions, micellar-type microemulsions, and certain (micellar-type) normal and reversed cubic phases. However, discrete self-assemblies are also important in other contexts. Adsorbed surfactant layers at solid or liquid surfaces may involve micellar-type structures and the same applies to mixed polymer-surfactant solutions. 

The cubic phases are also known as viscous isotropic phases - because they are As the name implies, these phases have structures based around one of several possible cubic lattices, namely the primitive, face-centred and body-centred. There are two very distinct aggregate structures, i.e. one comprised of small micelles, normal or reversed, and one based on three-dimensional bicontinuous aggregates. The normal and reversed structures that occur for both make a total of four classes. It is still not certain exactly which structures can occur for the different classes, but the overall picture has become much clearer during the past few years (46, 49-57), with more and more structures being identified. The first set of structures comprised of small globular micelles is labelled I , while the second group, the bicontinuous three-dimensional (3-D) micellar network, is labelled V . 

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