Liquid crystalline phases definition

Solubilization can be defined as the preparation of a thermodynamically stable isotropic solution of a substance normally insoluble or very slightly soluble in a given solvent by the introduction of an additional amphiphilic component or components. The amphiphilic components (surfactants) must be introduced at a concentration at or above their critical micelle concentrations. Simple micellar systems (and reverse micellar) as well as liquid crystalline phases and vesicles referred to above are all capable of solubilization. In liquid crystalline phases and vesicles, a ternary system is formed on incorporation of the solubilizate and thus these anisotropic systems are not strictly in accordance with the definition given above. 

More lipophilic surfactants form larger, nonspherical micelles, vesicles, or lyotropic liquid crystalline phases at rather low concentrations in water. For example, at temperatures above those where the chains form crystalline structures, phospholipids and other surfactants with two relatively long hydrocarbon chains typically form the lamellar liquid crystalline phase consisting of many parallel surfactant bilayers separated by water layers. The hydrocarbon interiors of the bilayers are rather fluid as in micelles. Of course, in this case a true phase separation occurs beginning at a definite surfactant concentration. 

The presence of liquid crystalline phases, their intermolecular structure and especially their state of dispersion definitely can affect interfacial tensions and interfacial tension transients (10), and may also influence other factors such as viscosity and the retention of surfactant during flow through a porous medium. 

A perhaps more significant example of a lyotropic liquid crystal is the cell membrane. The phospholipid bilayers of all cells behave as liquid crystals, maintaining a definite director and displaying only limited fluidity. Interestingly, most membranes are not pure phospholipids, but contain additives whose function is presumably to tune the structural and dynamic properties of the membrane. In animals, the most common additive is cholesterol, while plants use a similar steroid. As such, cell membranes can truly be thought of as cholesteric liquid crystalline phases. 

The liquid crystalline phase of dinuclear copper stearate has been known since 1938, and was reinvestigated in 1964 [38] but it was not until 1984 [39] that this mesophase was definitely characterized by Giroud-Godquin et al. as columnar discotic by X-ray diffraction. This was the first example of a thermotropic hexagonal discotic meso-... 

In Chapter 1 we introduced the term phase. A phase is a state that has a particular composition and also definite, characteristic physical and chemical properties. We may have several different phases that are identical in composition but different in physical properties. A phase can be in the solid, liquid or gas state. In addition, there may exist more than one distinct crystalline phase. This is termed polymorphism, and each crystalline phase represents a distinct polymorph of the substance. 

Chloroethyl dichlorophosphite is a colorless liquid having a specific gravity of 1.515 at 0°. It solidifies to a white solid at —142 1°. A second crystalline phase may be obtained by allowing the first phase to warm to room temperature. The higher-melting phase was not obtained directly from the liquid phase, nor was a definite temperature for the transition between the two phases observed. The boiling point has been reported to be 172 to 175° (747.8 mm.)1 and 162.4° (760 mm.).2... 

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