Mesophases classification

Thus, polymers with mesogenic groups in side chains form structural mesophases of the same types as low-molecular liquid crystals. This makes it possible to apply traditional mesophase classification for the description of the structure of LC polymers. At the same time, the structure of some of comb-like polymers (see Table 5) considered as crystalline, may probably be treated as one of highly-ordered smectic mesophases (SH or Sj), whose study is only started74). 

A major effort should be undertaken to clarify the open questions. It is hoped that the classification as offered in this review can serve to focus future work in mesophases of macromolecules. Of particular interest is the question of the involvement of condis crystals as intermediates in polymer crystal deformation. 

The optical texture of mesophase and resultant carbons is observed readily by means of a reflected polarized light microscope and may be classified according to the shape and size of the isochromatic units. Such a classification is useful to evaluate the properties of mesophase and carbons such as needle cokes. The mesophase has been defined as the intermediate state which shows optical anisotropy and is quinoline-insoluble at room temperature (5,51) (liquid crystal glass), although it is a viscous liquid crystal during the carbonization process (6). ... 

It is understood that manufacturing of liquid detergents that are unstructured in their commercial form may involve intermediate streams which are, in fact, structured fluids, such as surfactant solutions at high active concentrations, within anisotropic mesophase boundaries, or concentrated polymeric solutions and gels. Whether the source is raw material, premix, or final product, manufacturing operations for each of these classifications are discussed with a focus on any specific requirements or limitations due to the physicochemical form. 

There is a second particularity to be noted many virtually water-insoluble polymeric amphiphiles can be swollen to yield polymeric lyotropic mesophases, even if the miscibility gap is broad (Fig. 37). Such behaviour seems to be widespread for vinylic polymerized surfactants with side-chain spacers [126, 231, 331], I.e., neither polysoap behaviour implies the capability to form lyotropic mesophases, nor the presence of lyotropic mesophases the classification as polysoap. 

Thermotropic liquid crystals can be divided into three principal types through the mesophases they form, two of which will be introduced at this stage. This classification is based on the essential shape of the molecules and while,... 

Liquid crystals can be divided into two main classes those forming hquid crystalhne phases in the melt are called thermotropic and those forming hquid crystalhne phase in solution are referred to as lyotropic. Depending on the type of molecular order in the mesophase these classification can be broken down further into three main categories smectic, nematic, and cholesteric [4—7]. 

A tentative classification of mesophases was reported by Wunderlich [2], who divided mesophases into six different types of phases hquid crystals (LC), condis crystsds (CD), plastic crystals (PC) and the corresponding LC, CD and PC glasses. 

We have shown that this classification is sufficiently simple and general to include most important polymer solid mesophases identified so far. We are aware, however, that our classification of mesomorphic polymers, as well as alternative ones based on the different kinds of disorder which may occur in crystalline polymers, may not be exhaustive, since in many cases different kinds of disorder are interrelated and simultaneously present. For instance, in the case of polyacrylonitrUe, the irregular configuration of chains deter-... 

Like other states of matter, thermotropic mesophases are indefinitely stable at defined temperatures and pressures. Moreover, a thermotropic liquid-crystal-line material exhibits reversible phase transitions at well-defined temperatures. For example, the liquid crystal 4-n-pentyl-4 -cyanobiphenyl (5CB) melts from the solid to a nematic liquid crystal at 22.5°C and then from the nematic phase to the liquid at 35.0°C. As a consequence, the characterization and classification of thermotropic phases by microscopy also requires the use of an accurately controlled oven. 

In the following sections some of the more common liquid crystal textures utilized in the classification of thermotropic calamitic mesophases are described. It should be noted that similar examinations of defects are used to classify discotic, polymeric, and lyotropic phases. 

Figure 4 compares the total entropy change versus number of carbon atoms for the mesophase to isotropic transition for the three series. The difference between the aromatic and the cyclohexyl series is due partially to the early onset of the smectic phase in the saturated case, and partially to the smaller than normal entropy changes found in the aromatic series even when the smectic does appear. It is possible that the smectic formed in this latter case is of a different, less ordered class than found in the cyclohexyl series. Positive classification would be necessary to establish this. 

In addition to the well known liquid and plastic crystals a third mesophase the "conformational disordered crystal" exist. This classification results from the recognition that in the fully ordered crystal three kinds of order exist, namely positional, orientational and conformational. Loosing one kind of order and gaining the corresponding mobility leads respectively to liquid, plastic and "conformational disordered" crystals. On quenching in principle, the... 

Second, the ability of completely aromatic polyesters to form mesomorphic structures is interesting. Obviously, in such cases, the appearance of nematic LC states seems most probable. Furthermore, some polybenzoates (3-8) show mesophases, which cannot be described in terms of the conventional classification of liquid crystals, with respect to their arrangement, and which are similar to mesomorphic structures of flexible-chain polyorganosiloxanes (9) and polyphosphazenes (10). Finally, studies of relaxations and phase transitions in rigid-chain LC polyesters, in particular, their molecular mobility in the solid state, i.e., below the melting temperature of crystalline phase, are of great interest. 

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