Polymer orientation, characterization

The simple system of hardware and software described above provides data for orientation characterization of polymer specimens. The system is used to conduct research on a wide variety of materials rather than to provide analytical results for process control. 

Molecular Orientation Characterization of molecular orientation is important as many physical and mechanical properties of polymers depend on the extent and uniformity of the orientation [2,4,25]. Orientation can be measured by using a variety of techniques [2,4,25,33,34]. IR spectroscopy not only allows the characterization of amorphous and crystalline phases separately, it also provides morphological data and can be used to map orientation with high spatial resolution [35]. 

The use of orientational constraints represents only one solid-state NMR approach for polymer structural characterization. In the future, a combination of constraints will be used, no doubt, for such characterizations, in particular distance constraints from REDOR [45], or rotational resonance [46] will be helpful. Direct measurement of torsion angles using DRAWS [47], C7 [48] or rotor-synchronized 2D exchange [49] may also prove to be beneficial. 

Molecular order of LC main chain polymers is characterized by a high degree of conformational and orientational order of the polymer chains. The observed order parameters exceed those of conventional LCs by a considerable amount. The pronounced increase in orientational order from the monomers to the polymers can be rationalized by an intramolecular order transfer via highly extended spacers. 

Buffeteau T, Labarthet FL, Pezolet M, Sourisseau C. 2001. Dynamics of photoinduced orientation of nonpolar azobenzene groups in polymer films. Characterization of the cis isomers by visible and FTIR spectroscopies. Macromolecules 34(21) 7514 7521. 

Characterization of polymer orientation is most often accomplished via X-ray techniques which are suited to crystalline and paracrystalline regions (i-d). However, semicrystalline polymers present a complex system of crystalline, amorphous, and intermediate pluses ( -d) and complete characterization of semicrystalline polymers can only be achieved by application of a variety of techniques sensitive to particular aspects of orientation. As discussed by Desper (4), one must determine the degree of orientation of the individual phases in semicrystalline polymers in order to develop an understanding of structure-property relationships. Although the amorphous regions of oriented and unoriented semicrystalline polymers are primarily responsible for the environmental stress cracking behaviour and transport properties of the polymers, few techniques are available to examine the state of the amorphous material at the submicroscopic level. 

P-IOMBT in dichloroacetic acid was investigated in an alternating electric field. Experimental data show that the molecules of this polymer, just as those of other mesomorphic polymers, are characterized by a relatively high Kerr constant and the corresponding high dipole moment and orientational polar order. 

The purpose of this section is not only to confirm the identification, but also to characterize certain polymers and polymer types in detail. Although methods to determine microstructures and impurities, such as chemical inversions, modifications, and multiple bond formations, are different from polymer to polymer and are discussed separately, the methods used for the determination of density and crystallinity, as well as polymer orientation, are common to most polymers. Thus, the determination of crystallinity and density will be covered in this section, in Sec. 3.1, and likewise, the orientation of the polymer chain will be described in Sec. 3.2. The use of absorption coefficients to calculate properties, such as crystallinity, doublebond content, chain branching, and monomer ratios, is described in reference texts [14,15]. Today most work is performed by Fourier transform infrared (FTIR), and so an attempt has been made to feature coefficients from the latest reference sources, which include data acquired by FTIR. 

The formation of liquid-crystalline phases by covalent rigid, wormlike, and segmented chains has been extensively described [50]. Anisotropy and orientation are characterized at the molecular level by the order parameter and at the mesoscopic level by director orientation. In the case of supramolecular polymers orientation and growth may occur according to the following mechanisms ... 

If we assume that the development of a standard state, i.e. ideal metal-vacuum interface, was in fact the key to the advancements in metallic contact analysis we should also expect that this will also be the case in the polymer, or solid organic, friction or adhesion analysis. The consequence is that polymer surface characterization under various environments becomes the most important issue at hand. The achievement of the standard surface state in polymer or solid organic system will be most difficult due to the relatively weak intermolecular bonding forces and the normal existance of a wide range of impurities within the material itself. Ambient vacuum conditions are required for most of the physics oriented surface characterization techniques, e.g. LEED, FIM, Auger electron spectroscopy and under these conditions the surface can be modified by... 

It is interesting to note that, in the case of amorphous polar polymers, the temperature dependence of e and e" reflects alterations in the physical state of the system. This is due to the fact mentioned above that the absorption of sub-THz radiation is based on the orientation polarization of polar groups, which is determined by their mobility. As a polymeric system is heated up from low to high temperatures, various physical stages related to the mobility of structural elements are surpassed. As demonstrated in Figure 1.4, the temperature dependence of the dielectric response at constant frequency, typical for a polar amorphous polymer, is characterized by a succession of ascending steps in e and a corresponding series of e" peaks. 

The polymer is subjected to a biaxial stretching, which creates orientation both in the crystalline and in the amorphous phases. As in fiber spinning, many studies have been dedicated to orientation characterization, especially in the crystalline phase, but biaxial orientation requires more sophisticated methods. More recently, much effort has been devoted to the description of the morphology at the lamellar scale, for example, by electron microscopy. 

A liquid crystal display comprises a pair of substrates, transparent electrodes respectively formed thereon and a liquid crystal material layer inserted between the electrodes, and is characterized in that a liquid crystalline polymer orientation layer is formed on at least one of the liquid crystal material layers, and the liquid crystalline polymer orientation layer functions as an optical phase retardation film. The phase retardation of the light transmitting liquid crystal is compensated by the liquid crystalline polymer orientation layer, which enhances contrast. The liquid crystalline polymer layer can also be used as an optical phase retardation film. 

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