Liquid crystalline polymers crystal structure, effect

A review of the literature demonstrates some trends concerning the effect of the polymer backbone on the thermotropic behavior of side-chain liquid crystalline polymers. In comparison to low molar mass liquid crystals, the thermal stability of the mesophase increases upon polymerization (3,5,18). However, due to increasing viscosity as the degree of polymerization increases, structural rearrangements are slowed down. Perhaps this is why the isotropization temperature increases up to a critical value as the degree of polymerization increases (18). 

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. 

Sigaud et al. studied the effect of chemical structure of Hquid crystals on their miscibility with side chain liquid crystalline polymers ... 

Qin Y, Brydon DL, Mather RR, Wardman RH (1993) Fibers fi-om polypropylene and liquid crystal polymer blends 2. Effect of extrusion and drawing conditions. Polymer 34 1202 Seo Y, Hwang SS, Hong SM, Park TS, Kim KU (1995) Effect of die geometry on the structural development of a thermotropic liquid crystalline polymer in a thermoplastic elastomer matrix. Polym Eng Sci 35 1621... 

Lin Q, Jho JY, Yee AF (1993) Effect of drawing on structure and properties of a liquid crystalline polymer and polycarbonate in situ composite. Polym Eng Sci 33 789-798 Liu YJ, Sun XW (2008) Holographic polymer-dispersed liquid crystals materials, formation, and applications. Adv Optoelectron. 2008. Article ID 684349, 52 pages Matharu AS, Jeeva S, Ramanujam PS (2007) Liquid crystals for holographic optical data storage. Chem Soc Rev 36 1868-1880... 

Shandryuk GA, Matukhina EV, Vasiliev RB, Rebrov AV, Bondarenko GN, Merekalov AS, Gaskov AM, Talroze RV (2008) Effect of H-bonded liquid crystal polymers on CdSe quantum dot alignment within nanocomposite. Macromolecules 41 2178-2185 Shatalova AM, Shandryuk GA, Bondarenko GN, Kuptsov SA, Talroze RV, Plate NA (2003) Structure and thermal behavior of hydrogen-bonded liquid-crystalline polymers. Polym Sci 45 (2) 135-141... 

Conoscopy provides an extremely sensitive method with which to determine the degree of biaxiality. By the early 1990 s, conoscopic measurements had already indicated the presence of phase biaxiality in a nematic side-on liquid crystalline side-chain polymer [9]. However, the method s sensitivity is also its weak point because surface effects may induce optical biaxiality in an actual uniaxial system. For this reason, deuterium NMR was used to confirm phase biaxiality in a liquid crystalline polymer system similar to the one investigated with conoscopy by Leube [11-13]. Due to the fairly high viscosity of the polymeric samples, the tilt experiment, employed by Yu and Saupe to show phase biaxiality in a lyotropic liquid crystal [4], was used. The results obtained in this way are in good agreement with observations of optical textures in a biaxial cholesteric copolymer [16], where phase biaxiality disturbs the smooth optical periodicity of the cholesteric phase structure. 

We shall mention here another property of liquid crystalline polymeric systems. As in the case of low-molar mass liquid crystals, when electric and magnetic fields are applied, liquid crstalline domains get oriented along the direction of the field. Rearrangement of a polymer structure under the effect of a magnetic field was demonstrated in for a PBA-dimethylacetamide system. However, the processes of... 

The above results of phase behavior as summarized in Table I suggest that the observed macroscopic phase separation is directly related to the structure of the surfactant solution. There is no phase separation when the solutions are isotropic. But the added polymer induces phase separation only when a single liquid crystalline phase or a stable dispersion of liquid crystal particles in brine is present in the absence of polymer. The effect is the same for two different types of polymer and is independent of the polymer concentration over a fair range of composition. 

---