Mesophases lamellar

This parameter corresponds to cylindrical packing shapes. Surfactants and amphiphiles falling in this range often produce planar bilayers and lamellar mesophases. Such cylindrical building blocks also contribute to many... 

P. Kekicheff, H. K. Christenson. Forces measured in a swollen smectic lyotropic lamellar mesophase confined between solid surfaces. Phys Rev Lett (55 2823-2826, 1989. 

P. Kekicheff, P. Richetti, H. K. Christenson. Structure and elastic properties of lamellar mesophases from direct force measurements. Langmuir 7 1874-1879, 1991. 

P. Richetti, P. Kekicheff, P. Barois. Measurement of the layer compressibility modulus of a lamellar mesophase with a surface forces apparatus. J Phys II 5 1129-1154, 1995. 

L. and Mann, S. (2002) Chiral templating of silica-lipid lamellar mesophase with helical tubular architecture. Angewandte Chemie-International Edition, 41, 2988-2991. 

In binary mixtures of water, surfactants, or lipids the most common structure is the gyroid one, G, existing usually on the phase diagram between the hexagonal and lamellar mesophases. This structure has been observed in a very large number of surfactant systems [13-16,24—27] and in the computer simulations of surfactant systems [28], The G phase is found at rather high surfactant concentrations, usually much above 50% by weight. 

A. M. Seddon, H. M. Patel, S. L. Burkett and S. Mann, Chiral Templating of Silica-Lipid Lamellar Mesophase with Helical Tubular Architecture, Angew. Chem. Int. Ed., 2002, 41, 2988. 

Hexagonal mesophases can be recognized by their typical fan-shape texture (Fig. 7a). Lamellar mesophases typically show oily streaks with inserted maltese crosses (Fig. 7b). The latter are due to defects, called confocal domains, that arise from a concentric rearrangement of plane layers. In some lamellar mesophases these defects prevail. Hence no oily streaks occur but maltese crosses are the dominant texture (Fig. 7c). 

Figures 9a-c represent transmission electron micrographs of different lyotropic liquid crystals after freeze fracture without etching. The layer structure of the lamellar mesophase including confocal domains, hexagonal arrangement of rodlike micelles within the hexagonal mesophase, as well as close-packed spherical micelles within the cubic liquid crystal can be clearly seen.

Note 5 The lyotropic equivalent of a smectic A mesophase is known as a lamellar mesophase where layers of amphiphilic molecules are separated by layers of solvent, normally water, or by oil in an inverse lamellar mesophase. 

Figure 5. Thermal evolution of the SAXS patterns of the system C12PO4/ water (30/70 w/w) / Al[0 Pr]3 / H3PO4. (Freshly prepared equal molar amounts of C12P04, Al[0 Pr]3, and H3PO4). The lamellar mesophase is indexed dooi = 3.61 nm.

Figure 10. The activity of n-pentanol in micellar solutions of sodium octanoate with solubilized pentanol and in equilibrium with the lamellar mesophase D. The abscissa indicates the mole fraction of sodium octanoate in the system (15).

In two-component systems of association of colloid and water the sequence of phases, as the water content decreases, is micellar solution - hexagonally packed polar rods complex phases with rod-shaped aggregates lamellar mesophase D - crystalline surfactant. Some of these steps may be absent, depending, for example, on the temperature. 

Consider a lamellar mesophase, being macroscopically aligned so that the symmetry axis, referred to as the director, has the same direction throughout the sample. If the transformation from the molecular coordinate system to the laboratory system is performed via the director coordinate system (D), Equation 2 reads... 

Figure 5. 23Na NMR spectra of a lamellar mesophase sample of the system sodium octanoate-decanol-water. The rf field amplitude was increased in the order a,b,c,dt Peaks arising from double quantum transitions are clearly shown (cf. Figure 1).

In all our linewidth studies the width of the central peak was measured—i.e., the linewidth obeying Equation lib. In Ref. 45 we reported 23Na linewidth studies on a lamellar mesophase containing egg-yolk lecithin. The effect of cholesterol on the linewidth was investigated, and we found that with increasing cholesterol content in the phospholipid bilayers a marked reduction in the linewidth was observed. In accordance with similar investigations for simple soap-alcohol-water lamellar mesophases (42, 43) this is interpreted as a partial release of... 

Figure 6. Observed 23Na quadrupole splitting for lamellar mesophase samples of dimyristoyllecithin-cholesterol-2H20 as a function of the cholesterol concentration at four different temperatures 16°C ( ), 30°C (V), 40°C ( ), and 48°C (O). In all samples the salt solution (0.8M NaCl in 2H20) accounted for 25% of the total sample weight. The concentration of cholesterol is expressed as the percentage (by weight) of cholesterol in the lecithin-cholesterol mixture.

Figure 8. 23Na quadrupole splittings as a function of the sodium chloride concentration in the water layer for lamellar mesophase samples composed of 75% dimyristoyllecithin and aqueous salt solutions accounting for 25% of the total weight... 

Figure 9. Temperature dependence of the water deu-teron quadrupole splitting of a lamellar mesophase sample composed of 75 wt % 1 1 -mixture of dimyristoyl- and dipalmitoyliecithins and 25 wt % 0.8M NaCl in 2H20...

As micelles become larger, they have been shown to become more asymmetric, with their shape changing from spherical to cylindrical and lamellar. In lamellar mesophases (Figure 12.2c), the surfactant molecules are arranged in parallel sheets with the hydrocarbon tails forming the inner layers. The water is stratiLed between the sheets, hydrating the external polar head groups (Schot 1995). 

Hubbard PL, McGrath KM, Callaghan PT (2005) A study of anisotropic water self-diffusion and defects in the lamellar mesophase. Langmuir 21(10) 4340-4346... 

Fig. 23 The correlation length of the lamellar mesophase of the PEI-retinoate complexes depending on the molecular weight of the PEI. Reprinted with permission from [179]. Copyright 2000 American Chemical Society...

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