The Lamellar Mesophase

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. 

These concentration and temperature-dependent structural transitions can be qualitatively explained in terms of effective critical packing parameter (CPP), as developed by IsraelachvUi et al. [22]. According to this theory, amphiphiles 

Within the boundaries of a given mesophase the headgroups area normally increases with increasing hydration and decreases upon temperature rise. The length and the volume of the lipophilic tails are also greatly affected by a temperature increase. Stronger thermal motion of the tails eventually decreases the length of the tails but increases their volume. 

The CPP concept may only be used as a rule of thumb to predict transitions between various forms of LLC. For example, it was shown that it fails to predict the appearance of the inverse bicontinuous phases and an intermediate phase [12, 23]. This is the reason that a thermodynamic approach considering the total free energy of the LLC systems was applied by Seddon and coworkers [12, 24, 25], however, this is beyond the scope of this chapter. 

7 Hji Mesophase Composed of GMO/Triglyceride/ Water as Drug Delivery Systems 

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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.

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).

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...

Figure 1.4 T(7)-sections through the phase prism of the systems H20-n-octane-C6E2, C8E3, Q0E4 and C12E5 at an oil/(water + oil) volume fraction of = 0.5. In order to determine the respective X-point the phase boundaries are measured only for surfactant mass fractions 7 > 7. An increase of both the hydrophobic chain length / and the size of the hydrophilic head group j shifts the X-point to lower values of 7, i.e. the efficiency increases. Simultaneously the stability range of the bicontinuous one phase microemulsion shrinks dramatically due to the increased extension of the lamellar mesophase (La). (From Ref. [26], reprinted with permission of Elsevier.)...

FIG. 3 (a) Phase diagram of the dimethyldecylphosphine oxide-water system. C, crystals Lam, lamellar mesophase I, isotropic liquid, (b) Heat capacity jumps vs. concentration for the transition from the liquid to a two-phase state. Curve 1, Along the BE phase boundary in (a), I I -I- Lam transition curve 2, along EA, I I -I- C transition. Arrows indicate values exceeding the scale (theoretical Cp o°). (c) Transitions from the lamellar mesophase to the two-state phase. Curve 1, Along the BD phase boundary, Lam Lam -I-... 

The lamellar mesophase can be diluted with water and it has almost infinite swelling capacity, provided the lipid bilayers contain charged molecules and the... 

SmA Phase In contrast to polar compounds 41 exhibiting a partially bilayer S. phase (Sec. 4.2.2 of this chapter), the lamellar mesophase of biforked (O-cyano chain compounds 42a (also Sec. 4.2.2 of this chapter) is a monolayer S -... 

SmC Phase In the immense majority of cases, the lamellar mesophases displayed by these mesogens are Sc (Fig. 2b), except for non-polar penta- and hexacatenars, which do not exhibit any lamellar mesomorphism. For example, the X-ray pattern of magnetically aligned samples of biforked mesogens 16 (typically Table 5, compound with n = l,... 

The fact that these mesophases of various symmetries display the same crystalline structures (unchanged angle between crystalline phase and lamellar phase) and that lamellar-columnar transition enthalpies remain very weak (see the literature [27]) indicates that structural modifications between the crystalline phase and the lamellar mesophase are minor. 

In principle, one could generalize the considerations of Section 7.2.4 to a study of block copolymer mesophase ordering, by suitable identification of the order parameter of the transition. For the lamellar mesophase (Fig. 7.2), this order parameter is written in terms of concentration waves for the local concentration of component A, for instance... 

First studies " addressed the transition of symmetrical block copolymers (/ = N +Ni — 2) disordered melt to the lamellar mesophase (Fig. 

A ), indicating a dense packing and peipendicular orientation of the fluorocarbon chains. For the less hydrophilic surfactants in Series II, the areas were only a little larger, also revealing dense packing of the fluorocarbon chains (Fig. 4.11). The areas occupied by the more hydrophilic surfactants of Series I or II increased to values comparable to A = 47 A in the lamellar mesophases of... 

FIG. 12 Variation of structural parameters of model liquid crystal aggregates as a function of volume fraction of (pentanol + dodecane), p+d, as derived from X-ray diffraction data. (Top) Size of the nonpolar compartment. R p is the radius of the nonpolar core in the hexagonal mesophase Hi, and is the thickness of the nonpolar layer in the lamellar mesophase L . (Middle) Thickness of the hydrophilic mantle, tm. (Bottom) Available surface area per surfactant head group, a . Swelling lines 4PD ( ) 5PD (A) 6PD (o) 7PD ( ). These swelling lines correspond to the designation PD, where n-(10%) is the initial weight fraction of surfactant. Open symbols refer to Hj and filled symbols refer to the L phase. (From Ref. 38.)... 

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