Lamellar phases

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

Fig. 1 a-f. Various forms of surfactant aggregations in solution a Monolayer b bilayer c liquid crystalline phase (lamellar) d vesicle (liposome) e micelle f reverse micelle. (Reproduced from [39] with permission of PL Luisi)... 

Figure 5.2 Top-diagramatic representation of a detergent molecule, (a) Single tailed (b) double tailed (c) zwitterionic (d) bolamphiphilic. Bottom - different types of surfactant aggregates in solution (A) monolayer (B) bilayer (C) liquid-crystallin phase lamellar (D) normal micelles (E) cylindrical micelles (hexagonal) (F) vesicles (liposomes) (G) reversed micelles.

T extures of lyotropic mesophases have been the object of numerous observations by optical (1,2,3) and electronic (4, 5, 6,7) microscopy. Except for the pioneering work of Lehmann (1) and Friedel (2) who intended to identify the various kinds of defects which constitute the textures, the purpose of these observations was to recognize the different existing phases—lamellar, hexagonal (or in the soaps language neat phase, median phase, etc.)—in correlation with x-ray data. 

Fig. 57 Lam-phases (a-c) as formed by compound 182f with a linear lateral Rp-chain and (d,e) LamSm/cor/p2mm phase as formed by compound 182 g with a branched lateral chain (a) Lamiso phase = lamellar phase without order in the layers (b-d) in these Lam-phases the rod-like aromatic cores are organized on average parallel to the layer planes (b) LamN (lamellar nematic phase) = lamellar phase with only orientational order in the layers and between layers (c) LarnSm/ diS (lamellar smectic phase) = lamellar phase with orientational and positional order in the layers and only orientational order between the layers, a sliding of the layers with respect to each other is possible (d,e) in the correlated LamSm/cor phase there is also positional order between the layers and a p2mm-lattice is formed [8, 316, 317, 320-322]. (a-c) Reproduced with permission [321], copyright 2002, American Chemical Society (ACS)...

Figure 24 Crystallization time dependence of the thickness for the lamellae, the crystalline phase and the amorphous phase. lamellar, O crystalline phase, amorphous phase.

So what about the cubic phase In polycatenar systems, it is possible to rationalize the formation of cubic phases on the basis of surface curvature alone, which will be considered in subsequent sections. However, it can be argued that, for calamitic systems, these arguments do not hold—at least on their own—and that other factors are important. For example, if cubic-phase formation is due to surface curvature, it is not possible to explain why an Sa phase (lamellar and with no surface curvature) is seen at higher temperatures. An important factor is the presence of specific intermolecular interactions and in the case of the silver systems, these are the intermolecular electrostatic interactions resulting from the presence of formally ionic groups. This is consistent with the observation of cubic phases in the biphenylcarboxylic acids and hydrazines (Fig. 29), as well as with other materials. However, it is also evident that this is not the only factor, as no cubic phase is seen with anion chains shorter than DOS, while other studies with fluorinated alkoxystilbazoles showed that the position of fluorine substitution could determine the presence or absence of the mesophase observed in the unsubstituted derivatives (56). Thus, structural factors are clearly not negligible. 

Fig. 44. Maximum clearing temperature of liquid crystalline phases of a non-ionic polysoap 80 as function of the degree of polymeriza tion O cubic Ij phase, x hexagonal H, phase, lamellar L phase. (Data from [451] see also [126])...

Holyst and Schick [339] study the phase diagram and scattering of AB symmetric diblock copolymers diluted with A and B homopolymers (in equal concentrations) having the same chain length NA = NB = N as the copolymers. Constructing a Landau expansion, they show that the wave vector q vanishes at a critical copolymer concentration ordering transition there as that of a Lifshitz tricritical point, where the disordered phase, lamellar phase, A-rich and B-rich separated phases can coexist. The critical behavior near this point is expected to deviate strongly from mean field theory [339]. 

Let us first consider an ideal two-phase lamellar structure (see Figure 5.20) in which lamellae of phase A, of thickness da and uniform scattering length density pa, alternate... 

Figure 5.20 Scattering length density profile in the direction perpendicular to the lamella plane in the ideal two-phase lamellar system.

Figure 5.23 The correlation function y x) calculated for the ideal two-phase lamellar structure given in Figure 5.20.

There are some excellent review articles on different aspects of mesostructured materials, such as synthesis, properties, and applications. " Extensive research effort has been devoted to the exploitation of new phases (lamellar, cubic, hexagonal structures), expansion of the pore sizes (about 2-50 nm are accessible), and variable framework compositions (from pure silica, through mixed metal oxides to purely metal oxide-based frameworks, and inorganic-organic hybrid mesostructures). Another research focus is on the formation of mesostructured materials in other morphologies than powders, e.g. monolithic materials and films, which are required for a variety of applications including, but not limited to, sensors (based on piezoelectric mass balances or surface acoustic wave devices), catalyst supports, (size- and shape-selective) filtration membranes or (opto)electronic devices. The current article is focused... 

SAXS is a powerful tool to study the morphology of semicrystalline systems. The application of this technique is based on the electron density difference between the crystalline and amorphous phases (lamellar structure) in polymer systems. The crystalline (l ) and amorphous (IJ thicknesses can be obtained using this technique. Besides, the distance from one crystalline region to the next provides the size of a lamellar structure, also known as the long period (L). Other morphological features are the interface... 

Figure 17 Phase behavior as a function of salinity for the water - octane-SDS-pentanol or hexanol systems. In the sections presented the water/oil ratio = 1 and the alcohol/SDS ratio (A/S) = 2.W I,W II, W III = Winsor equilibria L = microemulsion phase = lamellar phase.

Despite most of the myelin studies having focused on growth and late timescale behavior the mechanism for their formation is still unknown. Penetration scans using onion phase (lamellar phase is presheared into multilamellar vesicles or onions) have shown that myelin formation can be suppressed (48), This implies that there formation is sensitive to bilayer organization in the lamellar phase. Dissolution of these onion phases also have interesting and exotic behavior (48, 49),... 

The phase diagram of monoolein/water as shown in Hg. 12.5 revealed complex structural behavior. At room temperature the following phase sequence existed upon increasing hydration lamellar crystalline phase (Lc) in coexistence with a 1 phase, lamellar mesophase (L ), and the inverted bicontinuous cubic mesophases-gyroid Ia3d and diamond Pn3m. Upon heating, at about 85 °C, the cubic phase is transformed into the Hn mesophase, followed by the micellar phase. 

Many different structures Liquid crystalline phases Lamellar Hexagonal Reversed hexagonal... 

Lyotropic liquid crystalline phases form by water solutions of amphiphilic (particularly biphilic) molecules [11, 12]. The building blocks of those phases are either bilayers, Fig. 4.18, or micelles. The form of the micelles can be spherical or cylindrical. Fig. 4.19a, b. For low concentration of oil in water, the micelles are normal (sketch (a), tails inside, polar heads outside, in water). For high craicentration, the structure is inversed ((b) and (c), water and polar heads inside, tails outside). Examples of the structure of some typical lyotropic phases (lamellar, cubic, hax-agonal) are shown in Fig. 4.20. Under a microscope they show characteristic features. 

The simultaneous collection of waxs and saxs data has its obvious advantages. The most important is that one is able to correlate structural changes on different length scales with each other. In some cases there are extra advantages. In the case of a two-phase lamellar system, the invariant obeys the following relation ... 

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