Micellar cubic phase

Light microscopy has been used in a number of contexts to characterize block copolymer morphology. For crystalline block copolymers, spherulitic structures that result from organization of crystalline lamellae can be examined using microscopy. In solutions, polarized light microscopy can reveal the presence of lamellar and hexagonal-packed cylindrical micellar phases. Cubic micellar phases are optically isotropic, and consequently cannot be distinguished from sols only on the basis of microscopy. 

Fig. 4.13 (a) Phase diagram for aqueous solutions of Pluronic 25R8 (PPOI5PE01WPPO 5) determined using SANS, SLS, DLS and rheometry (Morlensen 1997 Mortensen el al. 1994). Phases 1 and V are disordered micellar networks, V with excess water. Phases II and III are cubic micellar phases. Phase IV is a coexistence regime of micelles and crystalline layered PEO. (b) Schematic of the micellar network. 

Crystallization-induced phase separation can occur for concentrated solutions (gels) of diblocks [58,59]. SAXS/WAXS experiments on short PM-PEO [PM=poly(methylene) i.e. alkyl chain] diblocks revealed that crystallization of PEO occurs at low temperature in sufficiently concentrated gels (>ca. 50% copolymer). This led to a semicrystalline lamellar structure coexisting with the cubic micellar phase which can be supercooled from high temperatures where PEO is molten. These experiments on oligomeric amphiphilic diblocks establish a connection to the crystallization behaviour of related nonionic surfactants. 

Figure 16.1 Relationship between molecular shape, aggregate structure in dilute dispersions, phase behavior and packing parameter. Micellar phase (L,), cubic micellar phase (I), hexagonal phase (H), bicontinuous cubic phase (Q), La lamellar phase. Subscripts I and II indicate normal and inverted phases, respectively. From M. Scarzello, Aggregation Properties of Amphiphilic DNA-Carriers for Cene Delivery, Ph. D. Thesis University of Groningen, p 6, 2006...

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

Fig. 4.1 Top schematic illustration of micellar phases formed by the Pluronic copolymer P85 (PE 026PP0i9 PEO,6) with increasing temperature. Bottom small-angle neutron scattering patterns from sheared solutions in D20 of this copolymer (25wt%). The three columns (left-right) correspond to a liquid spherical micelle phase at 25 °C, a cubic phase of spherical micelles at 27 °C and a hexagonal phase of rod-like micelles at 68 °C (Mortensen 1993a).

For mesoporous silica (pore 0>2O A), successful results were obtained by the synthesis of the MCM family of silicates and aluminosilicates (of Section II.B). Their preparation is achieved by liquid crystal templating and micellar phases (hexagonal MCM-41, cubic MCM-48, laminar MCM-50)36,37 and further developments are currently reviewed38. 

Lipid cubic (51) and sponge (52) phases, as well as bicelles (53), are alternatives to detergents that have been applied successfully to membrane protein crystallization. In these instances, the protein is embedded in a lipid bilayer environment, which is considered more natural compared with the detergents that form micellar phases. In the recent high-resolution crystal structure of the human 32 adrenergic G-protein-coupled receptor, lipid cubic phase was used with necessary cholesterol and 1,4-butandiol additives (54). The cholesterol and lipid molecules were important in facilitating protein-protein contacts in the crystal. 

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. 

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. 

Similar to some zeolite syntheses, short-chain surfactants are used as templates in order to synthesize MCM. In aqueous solutions these surfactants form micellar phases, where the dissolved silicate species is made to condense. This way amorphous silicate walls, about 1 nm thick, originate between the micelles. Depending on the concentration of the surfactant, lyotropic, lamellar, hexagonal, and cubic phases develop which leads to varying siHcate structures. After thermal removal of the surfactant by calcination, materials with free pore systems are obtained. 

Disklike tetramer 38 of folic acid derivative containing oligo(glutamic acid) moieties has both thermotropic columnar and micellar cubic (Pm3n) phases [53-56]. By the addition of sodium salt, 38 forms supramolecular chiral structures in the columnar and cubic phases (Fig. 5.7). The formation of supramolecular chiral stmctures in the colunmar phase is due to the interactions between the hydrogen bonded disks and the ions [57, 58]. 

Therefore for thermotropic LCs, besides the usual columnar and micellar cubic LC phase, which can be considered as miceUar, vesicular LC structure are also... 

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.)...

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