Description of the Liquid Crystalline Phases

M. Marrucci and P. L. Maffettone, Description of the liquid-crystalline phase of rodlike polymers at high shear rates, Macromolecules, 22,4076 (1989). 

Surfactant-water systems show a rich polymorphism and in addition to isotropic solutions and crystals a range of different liquid crystalline phases can form [1,2]. The phase behaviour provides an essential clue to the understanding of the properties of surfactant systems and a large amount of experimental work has been devoted to determine phase equilibria. The theoretical description of the thermodynamic properties of the system has been studied to a much lesser extent. 

The liquid crystalline phase is most relevant to membranes in living systems and represents a good description for the cell membrane, even though real membrane nanoscale structure may be highly complex and dynamic. In the following section, we explore some of the interesting membrane phase behavior that has been seen in mixed-lipid membranes and its relevance to real biological systems. 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

The following table lists the liquid crystalline materials that are useful as gas chromatographic stationary phases in both packed and open tubular column applications. In each case, the name, structure, and transition temperatures are provided (where available), along with a description of the separations that have been done using these materials. The table has been divided into two sections. The first section contains information on phases that have either smectic or nematic phases or both, while the second section contains mesogens that have a cholesteric phase. It should be noted that each material may be used for separations other than those listed, but the listing contains the applications reported in the literature. 

However, it must be recalled that the Lifshitz theory was originally formulated23 25 for the model of beads (see Fig. 7 a). In this model, each monomer is represented as a material point thus, this model cannot be used for the description of the intramolecular liquid-crystalline phase. The description of the orientational ordering, requires the generalization of the Lifshitz consideration for the models, in which the state of an elementary monomer is defined not only by its spatial position but also by its orientation (see, for example, the models of Fig. 7 b-db Such a generalization will be our first aim in this section. 

The light microscope can be used to identify liquid crystalline phases, characterize molecular order, and quantify the distribution of defects. As such, the technique is seldom exploited to maximum advantage, particularly if studies are restricted to observations between crossed polars in transmitted light. Also, there is much scope for misinterpreting the observed contrast. TTiis chapter offers a systematic description of the options (and pitfalls) that are relevant to a research microscopist studying the structure of liquid crystalline polymers. 

Such a description encompasses the whole field of liquid crystals, where it is non-covalent, intermolecular interactions which determine the molecular organization leading to the various liquid crystalline phases or, in the extreme, to a totally disordered isotropic phase [2], The science of liquid crystals is really the art of balancing the various intermolecular interactions to achieve a desired liquid crystal phase rather than an ordered crystalline phase. Nature demonstrates this art in its highest form in the self-organization of lipids to produce liposomes and cellular membranes. 

As a starting point for considering the effect of impurity and solvent on crystallization, the growth and interaction process is examined in the framework of the fundamental solid-state, interfacial, and liquid phase (solute-solvent-impurity) chemistry. The solid-state chemistry is specific to a given crystalline material and the nature of the bonds (e.g., ionic, covalent, van der Waals, etc.) that hold the crystal structure together. A complete description of the solid-state aspects of crystal growth is beyond the scope of this... 

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