Liquid crystalline polymers structural model

The structure for different liquid crystalline phases of small molecules, that is the packing of the molecules, is in principle well established and depicted in many textbooks dealing with the liquid crystalline state. Structural models for liquid crystalline side-chain polymers in different liquid crystalline phases have also been proposed analogous to the packing of small molecules but were challenged by other research workers. 

Kupferman, R. Kawaguchi, M.N. Denn, M.M. Emergence of structure in a model of liquid crystalline polymers with elastic coupling. J. Non-Newton. Fluid Mech. 2000, 91, 255-271. 

By and large, mesogenic units make up most of the principal components in a liquid crystalline polymer. The structure and property of mesogenic units are of primary importance in determining properties of a polymer. It is thus very instructive to have a brief study of the structure and its influence on the property of mesogenic units with low mass liquid crystalline compounds as models and references. 

Numerical calculation of the X-ray scattering from a nematic system thus requires a simpler model than that presented in Figure 5.1. For further simplification, we can assume that the system consists of many very long hard rods, all of which are uniaxially oriented. Such a nematic system can be considered as a layer of oriented hard rods. As a result, a nematic system can be treated as a convolution of a hard rod with many randomly packed two-dimensional discs as shown in Figure 5.3. The form factor of such a simplified nematic system is that of the hard rod while the structure factor, i.e., interference function, is that of the two-dimensional randomly packed hard discs. An approximate analytical solution of the interference function of the two-dimensional randomly packed hard discs has been successfully derived by Ripoll and Tejero [3] in 1995 based on Percus and Yevick s approach. This simplified model can therefore be used to calculate the scatterings from nematic liquid crystalline polymers. 

Figure 8. Snapshots showing the structure of a model main chain liquid crystalline polymer for the model system with m = 6 and n = 10. Left isotropic phase at 500 K. Right the nematic phase at 350 K.

Fig. 5.119 A new structure model is shown [435] that has more detail than in Fig. 5.111 published earlier [430]. The model suggests there is a hierarchy, at least on the scale from 500 nm to the 1 nm size scale, specific to the liquid crystalline polymers. The key element shown is the microfibril, the same microstmctural unit basic to melt spun and drawn flexible polymers. (From Sawyer et al [435] reproduced with permission.)...

An interesting area, which involves chiral liquid crystal properties, is that of temperature sensors, used, for example, in the diagnosis of skin cancer, as well as in peripheral blood circulation problems. Another application in the medical field is represented by nematic elastomer films or fibers of liquid crystalline polymers with mesogene in the side chain, that can be used in the manufacture of muscle prosthesis [28]. To optimize their performance for different applications, the current knowledge on the relationship between the structure and properties of liquid crystals should be extended. In addition to further development of liquid crystals and their applications, the liquid crystal theories represent a sound basis for other areas of interest. For example, liquid crystals can be used as model compounds for the study of molecular interactions and of their effects on self-organization in supramolecular chemistry. 

A difference in the defect structure of PBLG in BA versus PBLG in m-cresol may prove to be the underlying cause of this alignment behavior. Regardless, the results exemplify the need for a broader choice of model liquid crystalline polymer solutions when examining the flow-induced structure in liquid crystalline polymer solutions. Moreover, a more complete understanding of the important parameters that affect the flow of LCP solutions is needed so that a more universal theory can be developed which can predict flow behavior of non-model LCP solutions. 

The morphology of polymer blends, block copolymers, semicrystalline polymers and liquid-crystalline polymers can be assessed by microscopy. The morphology can be directly observed and the structure is in most cases assessed without the need for any sophisticated model. Small-angle X-ray... 

The SEM images of PBO fibers show fibrillar structure. A hierarchical structure model [81] was proposed for oriented liquid crystalline polymers, in which a fiber is made up of macrofibrils. 

Another typical model LCP is PI-14-5CN. It is a nematic side-chain liquid-crystalline polymer (SCLCP), with thechemical structure [54]presented in Figure 11.3. 

Table 16.1 Schematic illustration of structural models of liquid crystalline polymers (Chen et al. 2010)... 

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