Mesogenic groups optical properties

Phase Behavior and Electro-optic Properties. With the great potential of PSFLCs, it is important to understand the changes induced by the polymer network on the FLC properties. In order to do so, two different non-mesogenic monomers, HDDA and PPDA, have been used. The structure of these monomers is quite similar (See Figure 1) with the only difference being that the phenyl group in PPDA is replaced with a six carbon alkyl chain for HDDA. These monomers, despite their structural similarity, have much different physical properties and consequently the polymers formed from HDDA and PPDA may also influence the FLC phase and electro-optic behavior differently. 

This review deals with LC polymers containing mesogenic groups in the side chains of macromolecules. Having no pretence to cover the abundant literature related to thermotropic LC polymers, it seemed reasonable to deal with the most important topics associated with synthesis of nematic, smectic and cholesteric liquid crystals, the peculiarities of their structure and properties, and to discuss structural-optical transformations induced in these systems by electric and magnetic fields. Some aspects of this topic are also discussed in the reviews by Rehage and Finkelmann 27), and Hardy 28). Here we shall pay relatively more attention to the results of Soviet researchers working in the field. 

Figure 2. Schematic structure of side chain liquid crystal polymers with dichroic dyes (imparting nonlinear optical properties) and mesogenic side groups.

Interactions between side chains leading to unique dynamo-optical properties are particularly pronounced for comb-like molecules with mesogenic side groups. 

Shibae%, V. R, Kostromin, S. G., and Ivanov, S. A. Photoregulation of the optical properties of comb-shaped polymers with mesogenic side groups and the problems of data recording. Po/ym. Scf. 39, 118 (1997). 

Nonequilibrium electro-optical properties of polymers with mesogenic side groups are also very distinctive. In alternating electric fields, low-frequency dispersion of the Kerr effect is observed. The range of dispersion depends on the molecular weight of the fraction, just as for lyotropic polymers. Fig. 9 shows the dependence of the relative value of the Kerr constant at the field frequency V and at v=0 on the field frequency for solutions of... 

Polymer (la) in principle has the same chemical constitution as polymer (lb), however, the rigid mesogenic benzoic acid phenyl-ester group is linked to the backbone by the short flexible spacer of only two methylene units. Owing to their chemical constitution strong interactions of the main chain and the mesogenic side groups are to be expected. Actually this polymer exhibits unusual optical properties No typical nematic... 

The results of the present work demonstrate that the cholesteric mesophase of polymers having mesogenic side groups is, in many aspects, similar to that of low molecular cholesterics. The presence of the polymeric chain results, however, in the appearance of some specific features in the behavior of such systems. The possibility to quench the cholesteric structure by vitrification of polymers is worth emphasizing explicitly. The properties of polymeric cholesterics discussed above are far from covering the array of specific features particularly intrinsic to polymeric liquid crystals. The essential effect of molecular parameters on their structure and optical properties constitute one of these features. This problem will be treated in subsequent publications. 

A question to be asked is whether the macro-mechanical deformation of liquid crystal elastomers or stress fields can produce effects similar to those observed in conventional liquid crystals under external fields. Studies using the stress optical properties, conoscope, and X-ray diffraction have shown that applied mechanical fields do have a profound effect on the arrangement of the mesogenic groups in LC network [26]. 

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