Hexagonal liquid crystalline phase

The phase behavior of a-ester sulfonates has been studied in detail with methyl laurate and methyl palmitate [58]. In both cases, at higher temperatures, as the surfactant concentration increases, there is a transition from an isotropic solution to a hexagonal liquid crystalline phase and finally, at high surfactant concentrations, to a lamellar liquid crystal (Fig. 4). The crystal/liquid-crys-tal phase transition occurs at even higher temperatures as the chain length increases. On the other hand, chain length has practically no influence on the... 

Region I. Relative to lamellar liquid crystalline phase Region IIl. Relative to hexagonal liquid crystalline phase Region IV. Relative to isotropic micellar solution... 

Francois and Varoqui (34) measured diffusion rates of Cs+ in the hexagonal liquid crystalline phases of the water-cesium myristate and water-cesium laurate systems. In each case diffusivity was obtained as a function of temperature for a given liquid crystal composition. Values of 1-2 X 10"5 cm2/sec were reported for 60°-80°C. Diffusivity was about an order of magnitude lower in the gel phase of the cesium myristate system. 

Fig. 2.20. Phase diagram (at 25 °C) from the work by Ekwall and co-workers (cf. Refs.8 86)) for the three-component system hexadecyltrimethylammonium bromide (CTAB) - hexanol -water. Li denotes a region with water-rich solutions L2 a region with hexanol-rich solutions D and E are lamellar and hexagonal liquid crystalline phases, respectively. In the figure are also schematically indicated the structures of normal (Lj region) and reversed (L2) micelles as well as of the liquid crystalline phases. (From Ref.9Sb...

Huang LM, Mitra AP, Wang HT, Wang ZB, Van YH, Zhao D. 2002. Cuprite nanowires by electrodeposition from lyotropic reverse hexagonal liquid crystalline phase. Chem Mater... 

The primary progress achieved in the field of transdermal delivery uses cubic and hexagonal liquid crystalline phases [43, 62, 63]. This chapter is focusing on the current knowledge of topical, mainly transdermal routes of liquid crystal-based delivery systems. 

The penetration of CysA in the skin and its percutaneous delivery were assessed in an in vitro model of porcine ear skin using a Franz diffusion cell. The quantity of CysA detected in SC and in the epidermis and dermis layers [E + D] was indicative of drug penetration into the skin, whereas the amount of drug in the receptor phase was indicative of its percutaneous dehvery. The in vitro skin penetration and percutaneous delivery of the cubic and hexagonal liquid crystalline phases compared to the control formulation (ohve oil) containing CysA are depicted in Fig. 12.16. 

Different materials such as salts, free fatty acids, polyols, fatty alcohols, fatty esters, and per-fiunery components can influence the formation of liquid crystalline phases. Free fatty acids and fatty alcohols promote the formation of lamellar liquid crystalline phase [26], One can expect solid, isotropic solution, and hexagonal liquid crystalline phases coexisting in normal soaps, but in superfatted soaps, part of the hexagonal liquid crystalline phase is converted to lamellar, which is responsible for product softness during processing. 

Fig. 52. X-ray diffraction data concerning the hexagonal liquid crystalline phase formed by NaC and lecithin in water at maximum swelling of the liquid crystalline phase. Data taken from (3). Vertical axis in A horizontal axis lecithin-bile salt (NaC) molar ratio. Dt = distance from the center of one cylinder to another (X-ray diffraction). Dc = diameter of the lecithin-bile salt cylinder. /> , = thickness of water layer between the cylinders. Insert on the left gives two-dimensional packing of lecithin-bile salt cylinders in a compact hexagonal array.

Fig. 59. High-resolution 60 Me NMR spectra of liquid crystalline phases formed by NaC and lecithin in D2O. Top—hexagonal liquid crystalline phase formed by 35% NaC-30% lecithin-35 % D2O. Bottom—lamellar liquid crystalline phase formed by the mixture 10% NaC-90% lecithin-40 % D2O. The peak at 5.4 ppm is due to HDO and H2O. Note high resolution peaks due to choline at 6.7 ppm and the methyl groups about 8.7 ppm. 33.4X.

I), then a hexagonal phase (zone III), and finally a micellar phase (zone IV). As NaC is added to sodium oleate, the lamellar phase (zone I) disappears abruptly, showing that very little bile salt can be incorporated into the lamellar liquid crystalline phase formed by sodium oleate. At low concentrations of water, a viscous isotropic phase having a cubic lattice by X ray is present (zone II). There is a large zone of hexagonal liquid crystalline phase (zone III) which can contain up to 65% NaC by weight. This phase has been studied by X-ray diffraction at a constant 40 % water, and the distance between... 

Fig. 62. The quaternary system cholesterol-lecithin-sodium cholate-water. The tetrahedron on the left is a representation of this four-component system. The five triangles of decreasing size at the right of the diagram schematically represent cuts taken parallel to the base of the tetrahedron (lecithin-sodium cholate-water), to which a given amount of cholesterol at different overall cholesterol concentrations (2%, 4%, 6%, 25%) has been added. Choi, cholesterol L, lecithin NaC, sodium choiate W, water. Also a, lamellar liquid crystalline phase b, cubic liquid crystalline phase c, hexagonal liquid crystalline phase d, micellar phase (42). Expressed as wt%.

Figure 11.17. Arrangement of DNA or PBLG molecules in the columnar hexagonal phase. (Reprinted from J. Mol. Biol. 218, F. Livolant, Supramolecular organization of double-stranded DNA molecules in the columnar hexagonal liquid crystalline phase, pp. 165-181 1991, by permission of Academic Press [28].)...

Figure 24 Oscillatory behaviour of a nonionic hexagonal liquid crystalline phase, [24],...

Fig. 2 Phase diagram of water/POE(10) system as a function of tern- Fig. 3 Phase diagram of water/POE(20) system as a function of perature. Hii hexagonal liquid crystalline phase, Ij discontinuous temperature cubic phase. Vi bicontinuous cubic phase...

Phase notations F, reverse hexagonal liquid crystalline phase, Li and L2, isotropic solution phases... 

Gemini cationic surfactants with arginine head groups were recently synthesized and found to give rise to a hexagonal liquid crystalline phase at low concentration and temperature [139]. 

In soap bar processing free fatty acid is usually added in formulations to create so-called super-fatted soap. An acid-soap complex with a fixed stoichiometric ratio between alkaline soap and the fatty acid is formed. For example, the ratio of potassium acid soap is 1 1 while sodium soap forms acid soaps with various ratios. The fixed ratio complex exits not only in anhydrous crystalline phase but also in a hydrous liquid crystalline phase (11, 12). Oleic acid and its potassium soap form a 1 1 complex acid soap when equal molar acid and soap are mixed. Above the Krafft boundary, the acid soap in water forms a lamellar liquid crystal phase at low surfactant concentration, from a few percent, and the lamellar liquid crystal phase extends to ca 60% surfactant concentration. A hexagonal liquid crystal phase is formed after the lamellar liquid crystal phase with further increasing the surfactant concentration. This phase behavior is different from the soap and water phase behavior, in which the hexagonal liquid crystalline phase is formed first followed by the lamellar liquid crystalline phase. Below the Krafft boundary the acid soap complex forms a solid crystal and separates from water (4). 

Mixed Soap Crystals in Nonsuper-Fatted Formulation Soap bars consist of mixture of soaps with different chain lengths and chain saturations. They are classified as soluble soaps and insoluble soaps. The soluble soaps usually form a hexagonal liquid crystalline phase with water, as shown in Fig. 2.1, which dissolves in water during washing and provides lather. The insoluble soaps stay in crystalline formats in the bar and provide mechanical strength. The solid crystals present in a soap bar can include kappa, zeta, eta, and delta phases. 

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