Crystal structures, polymers surface regions

The recent example of the ab initio structure determination of the polymer electrolyte Poly (ethylene oxide)6 LiAsFe by Bruce et is a notable example of the complex structures that can be determined from powder diffraction on a pulsed neutron source. Polymer electrolytes consist of salts dissolved in solid high molecular weight polymers, and represent a unique class of solid coordination compounds. Their importance lies in their potential in the development of truly all-solid-state rechargeable batteries. The structure of the 6 1 complex is particularly important, as it is a region where the conductivity increases markedly. The structure of the complex is distinct from all known crystal structures of PEO salt complexes (see Figure 7). The Li-i- cations are arranged in rows, with each row located inside a cylindrical surface formed by two PEO chains, with the PEO chains adopting a previously unobserved conformation. Furthermore the anions are located outside the PEO cylinders and are not coordinated with the cations. 

Polymer, as solid, has imperfect supermolecular structure it has amorphous regions, regions without structures and ciystalline regions with well packed maeromolecules. Lamellar monociystals (lamellae) in which maeromolecules are placed perpendicular to wide surface of a plate are the main structure of polymer crystalline part. Usually length of macromolecule being crystallized greatly exceeds thickness of lamella and, to be placed into the crystal, macromolecule must repeatedly fold. 

A difficulty arises because the photonic crystal structures for the visible region are not easy to fabricate. However, in this chapter we describe a facile extrusion method for fabricating polymers with a ID structure like that shown in Figure 2. The nanolayered polymeric structures can consist of many thousands of layers and have a modulation in the nonlinear refractive index in the direction normal to the surface of the layers. Such materials are the nonlinear analogue of polymeric multilayer interference mirrors. (10,11,12) They are also the ID analogue of the 2D photonic crystals studied by Lin et. al. (13) The latter workers demonstrated that photonic crystals do indeed provide an effective method for converting an intensity dependent refractive index into an intensity dependent transmission. 

Even if one solves the indexing problem and then proceeds with the analysis by an evaluation of measured reflection intensities, one cannot expect to achieve an accuracy in the crystal structure data that would be comparable to those of low molar mass compounds. This is not only a result of the lack of single crystals, but also represents a principal property In small crystallites, as they are found in partially crystalline polymers, lattice constants can be affected by their size. Furthermore, disorder is more frequently found as in low molar mass systems, in particular, in the region near the fold surface. 

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