Lyotropic lamellar systems

The stack of lyotropic lamellae stabilized by the mechanism suggested by Hel rich.  

For individual lamellae, which interact via collisions, the entropic confinement pressure is  

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Figure 5. Schematic representations of lyotropic lamellar systems, (a) Bilayers of phospholipids (one polar end and two paraffinic chains) are more or less separated by water (after Schmitt and Palmer [18]). (b) A bilayer (sketched on a different scale) with two parallel surfaces (or two parallel lines in cross-section), (c) Myelinic finger, with cylindrically nested bilayers, the number of which is strongly reduced (possibly by a factor of 10 ), compared to the lecithin fingers in (cO- (d) The bilayers parallel to the preparation plane are said to be horizontal and form a dark background (D) between crossed polarizer, whereas oblique or vertical bilayers appear bright (B), mainly if they extend at AS from the orientation of the polarizers, as shown in (dO for lecithin, (e) Bilayers that were initially horizontal often corrugate in one or two directions to form domes and basins, each appearing as a Maltese cross (M) when observed between crossed polarizers (e ).

Lyotropic lamellar systems are very similar to thermotropic smectics, and their elastic free energy is identical to that of SmA given in Eq. (4.34). In lyotropic lamellar systems, the origin of the layer compression modulus B is the steric repulsive interaction energy. This can be visualized as illustrated in Figure 4.20. If a stack of membranes, formed, e.g., by lipid bilayers, is placed between two parallel walls, violent thermal out-of-plane fluctuations of the membranes exert a pressure p on the walls. 

Here Q is the area enclosed by the loop, and we utilized the Stokes theorem to see that, in the area of dislocations V x ii 5 0 / i-e-, bend ((V x ii) x n ) and twist Vxn) n) deformations are possible. Parabolic focalconic arrays induced by dilation of layers have importance in lyotropic lamellar systems, too.2 ... 

MAS has been applied to a highly viscous cubic phase of a lyotropic LC formed by 1-monooleolyl-rac-glycerol and water in order to obtain liquid-like and 13C spectra.330 Deuterium, sodium, and fluorine NMR spectroscopy have been applied to study the phase behaviour of several dilute lamellar systems formed by low concentrations of an ra-hexadecylpyridinium salt, a sodium salt (e.g., NaBr, NaCl, or sodium trifluoroacetate), 1-hexanol, and D20.331 The 2H, 19F, and 23Na splittings were used to monitor the phase equilibria. The last two studies are motivated by the search of new lyotropic LC for the alignment of biomolecules. 

In a lipid/water system, the thickness of the bilayers is constant, and the unbinding transition can occur, in principle, by varying the Hamaker constant or temperature.22 For lyotropic lamellar liquid crystals, hyperswelling in a liquid of one kind might also occur if the lamellae of the other kind are thin enough and hence unbound. However, thin lamellae might lead to a positive contribution to the free energy (since the repulsive forces overcome at short distances the van der Waals attraction), and hence the lamellar phase can become unstable. 

II.2. Charged Lyotropic Lamellar Liquid Crystals. In the case of a charged system, two changes in the system of eqs 17 must be made.80 81 First y should be replaced in eq 17a, for the surfactant, by y + fy=mole fraction of the surfactant in water, Xsw, should be replaced in the same equation by the mole fraction of the surfactant in water, in the vicinity of the interface CX SW). Assuming that the surfactant in the aqueous phase is totally dissociated, the concentration of surfactant near the interface (Xsw) can be related to the average surfactant concentration in the water phase, Xsw, by using the equilibrium and mass balance relations... 

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. 

Makai M, Csanyi E, Eros I, Dekany I. Preparation and structural determination of lyotropic lamellar liquid crystalline systems of pharmaceutical importance. Acta Pharmaceutica Hungarica. 2002 73(2) 71-76. 

For some spectroscopic applications lyotropic lamellar mesophases of soaps may be of great value. Lamellar liquid crystals are formed in sodium decanoate-decanol-water systems [14]. A convenient system is obtained by mixing 28 wt% sodium... 

In these lectures we have seen that the lyotropic lamellar phase exhibits in a pronounced manner, the Landau-PeierIs effect for dilute stacked membrane systems with low rigidity k(> = kgT. The x-ray structure factor was seen to exhibit power-law behavior with the exponent (d) describing the algebraic decay of layer correlations. In turn, f (d) is directly related to the intermembrane interactions. 

Lyotropic lamellar phases are made by equidistant organic bilayers regularly separated by water or oil. Some of these lamellar phases show very interesting textures of FCD s. This is the case when the lamellar phase is between two phases of different topology. In the system studied by Boltenhagen et a/.(1991,1992), both types of FCDI and II have been observed. 

These structures are extensively described in the current literature (Fanum, 2008 Friberg, 1976 Birdi, 2002 Holmberg, 2004 Somasundaran, 2006). Even within the same phases, their self-assembled structures are tunable by the concentration for example, in lamellar phases, the layer distances increase with the solvent volume. Lamellar structures are found in systems such as the common hand soap, which consists of ca. 0% soap + 20% water. The layers of soap molecules are separated by a region of water (including, salts etc.) as a kind of sandwich. The x-ray diffraction analysis shows this structure very clearly. Since lyotropic liquid crystals rely on a subtle balance of intermolecular interactions, it is more difficult to analyze their structures and properties than those of thermotropic liquid crystals. Similar phases and characteristics can be observed in immiscible diblock copolymers. 

Figure 4. Thermal evolution of the SAXS patterns of the system C12PO4/ water (30/70 w/w). The lamellar lyotropic phase is indexed doot - 9.83 nm (20°C).

In conclusion, the synthesis of mesostructured aluminophosphate / surfactant materials in alcoholic systems yields a mixture of an inverse hexagonal and a lamellar phase, the latter of which is more stable, as its formation is relatively favoured by higher temperatures and/or longer reaction times. The synthesis is highly cooperative the surfactant / alcohol systems without the inorganic species do not show any lyotropic behaviour. 

Lxotmpii liquid crystals possess at least two components. One of these is water and the other is amphihle (a polar head group attached to one or more long hydrocarbon chains). In the lamellar form, water molecules are sandwiched between the polar heads of adjacent layers while the hydrocarbon tails lie in a nonpolar environment. Lyotropic liquid crystals have very complex structures, but occur abundantly in nature, particularly in living systems. See Fig. 3. 

The chemical potentials measured so far do not allow the formulation of thermodynamic criteria for the formation of lyotropic mesophases. Some qualitative remarks, however, can be made. Of particular interest are Ekwall s studies of the relations between the water binding of the mesophases, their ionization, x-ray parameters, and vapor pressures (4). For common soaps at room temperature mesophases can be observed only in the presence of amounts of water that hydrate the ionic and polar groups. Hydration is therefore characteristic of aqueous lyotropic mesophases as well as micellar systems (1, 2, 3). The binding of counterions to the micelles and to the mesoaggregates seems to be of a similar electrostatic nature. The addition of NaCl greatly affects the lamellar phase D and, to a lesser extent, phase E in these phases the counterions are more strongly bound than by micelles in the solution... 

Little work seems to have been done on thin oriented layers of lyotropic liquid crystals although there is one recent report of preparation of such a layer of the lecithin-water lamellar phase (JO). As indicated by Brochard and de Gennes (II), theories of the hydrodynamics of thermotropic smectic materials can be adapted to describe oriented layers of lamellar liquid crystal in lyotropic systems. 

The widespread interest in transport across membranes of living cells has led to studies of diffusion in lyotropic liquid crystals. Biological membranes are generally thought to contain single bimolecular leaflets of phospholipid material, leaflets which are like the large, flat micelles of lamellar liquid crystals. No effort is made here to review the literature on transport either across actual cell membranes or across single bimolecular leaflets (black lipid films) which have often been used recently as model systems for membrane studies. Instead, experiments where lamellar liquid crystals have been used as model systems are discussed. 

Experiments by Muller et al. [17] on the lamellar phase of a lyotropic system (an LMW surfactant) under shear suggest that multilamellar vesicles develop via an intermediate state for which one finds a distribution of director orientations in the plane perpendicular to the flow direction. These results are compatible with an undulation instability of the type proposed here, since undulations lead to such a distribution of director orientations. Furthermore, Noirez [25] found in shear experiment on a smectic A liquid crystalline polymer in a cone-plate geometry that the layer thickness reduces slightly with increasing shear. This result is compatible with the model presented here as well. 

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