Liquid crystalline systems cubic

Cubic liquid crystalline systems have been described as clear, stiff gelsJ As such, they show shear thinning after an apparent yield stress has been exceeded. The viscoelastic properties are also typical for the gel character a broad linear viscoelastic range and a frequency-independent elastic component, which is considerably higher than the viscous component, are observed. ... 

Rizwan SB, Dong YD, Boyd BJ, Rades T, Hook S (2007) Characterisation of biconti-nuous cubic liquid crystalline systems of phytantriol and water using cryo field emission scanning electron microscopy (cryo FESEM). Micron 38 478M 85... 

Sample Preparation. Liquid crystalline phases, i.e. cubic and lamellar phases, were prepared by weighing the components in stoppered test tubes or into glass ampoules (which were flame-sealed). Water soluble substances were added to the system as water solutions. The hydrophobic substances were dissolved in ethanol together with MO, and the ethanol was then removed under reduced pressure. The mixing of water and MO solutions were made at about 40 C, by adding the MO solution dropwise. The samples for the in vivo study were made under aseptic conditions. The tubes and ampoules were allowed to equilibrate for typically five days in the dark at room temperature. The phases formed were examined by visual inspection using crossed polarizers. The compositions for all the samples used in this work are given in Tables II and III. 

Fig. 2.18. Phase diagram of the dodecyltrimethylammonium chloride-water system. F denotes isotropic solution phase, M normal hexagonal liquid crystal, N lamellar liquid crystal and C and C cubic liquid crystalline phases. (From Ref.84))...

Figure 2. Ternary phase diagram of the system didodecyldimethylammonium bromide / water / hexene at 25°C. The nomenclature is cub cubic phase Lamj and Lam2 lamellar phases l.c. liquid crystalline, inverted hexagonal phase L2 microemulsion phase, with curvature toward water. (Courtesy of K. Fontell).

A liquid crystal is a general term used to describe a variety of anisotropic structures formed by amphiphilic molecules, typically but not exclusively at high concentrations. Hexagonal, lamellar, and cubic phases are all examples of liquid crystalline phases. These phases have been examined as drug delivery systems because of their stability, broad solubilization potential, ability to delay the release of encapsulated drug, and, in the case of lamellar phases, their ability to form closed, spherical bilayer structures known as vesicles, which can entrap both hydrophobic and hydrophilic drug. This section will review SANS studies performed on all liquid crystalline phases, except vesicles, which will be considered separately. Vesicles will be considered separately because, with a few exceptions, generally mixed systems, vesicles (unlike the other liquid crystalline phases mentioned) do not form spontaneously upon dispersal of the surfactant in water and because there have been many more SANS studies performed on these systems. 

We wish to study the effects of planar Couette flow on a system that is in the NPT (fully flexible box) ensemble. In this section, we consider the effects of the external field alone on the dynamics of the cell. The intrinsic cell dynamics arising out of the internal stress is assumed implicitly. The constant NPT ensemble can be employed in simulations of crystalline materials, so as to perform dynamics consistent with the cell geometry. In this section, we assume that the shear field is applied to anisotropic systems such as liquid crystals, or crystalline polytetrafluoroethylene. For an anisotropic solid, we assume that the shear field is oriented in such a way that different weakly interacting planes of atoms in the solid slide past each other. The methodology presented is quite general hence it is straightforward to apply for simulations of shear flow in liquids in a cubic box, as well. 

A central issue in the field of surfactant self-assembly is the structure of the liquid crystalline mesophases denoted bicontinuous cubic, and "intermediate" phases (i.e. rhombohedral, monoclinic and tetragonal phases). Cubic phases were detected by Luzzati et al. and Fontell in the 1960 s, although they were believed to be rare in comparison with the classical lamellar, hexagonal and micellar mesophases. It is now clear that these phases are ubiquitous in surfactant and Upid systems. Further, a number of cubic phases can occur within the same system, as the temperature or concentration is varied. Luzzati s group also discovered a number of crystalline mesophases in soaps and lipids, of tetragonal and rhombohedral symmetries (the so-called "T" and "R" phases). More recently, Tiddy et al. have detected systematic replacement of cubic mesophases by "intermediate" T and R phases as the surfactant architecture is varied [22-24]. The most detailed mesophase study to date has revealed the presence of monoclinic. 

Figure 5.1 Reaction profiles for reaction between 4-terf-butylbenzyl bromide and potassium iodide using a 1 1 0 (a) or a 1 1 (b) molar ratio of the reactants. The reactions were performed in a decane-water two-phase system, in a microemulsion, in hexagonal or cubic mesoporous materials and in hexagonal or cubic liquid crystalline phases.

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