Domain crystallite

WAXS studies were also performed on polymer fibers from SMPU with SME [61] to investigate structural differences between bulk material (SMPU) and spun fibers (SMF). It could be shown that the degree of crystallinity of a certain SMF was higher than that of the corresponding SMPU. In this way, it was verified that the spinning process could prompt the formation of hard domain crystallites. In the same study SAXS experiments were also performed to investigate the SMP structure on the next higher level of hierarchy. 

Polymers in the solid state tend to be composed of both ordered crystalline domains (crystallites) and disordered amorphous domains. 

Polymers, like small organic molecules, tend to crystallize upon precipitation or as they are cooled from a melt. Acting to inhibit this tendency are their very large molecules, which tend to slow diffusion, and their sometimes complicated or irregular structures, which prevent efficient packing of the chains. The result is that polymers in the solid state tend to be composed of both ordered crystalline domains (crystallites) and disordered amorphous domains. The relative amounts of crystalline and amorphous domains differ from polymer to polymer and often depend upon the manner in which the material is processed. 

Figure 2. Schematic structure of an ionomer containing three phases ionic domains, crystallites, and amorphous regions.

The breadth of the peaks in an x-ray diffractogram provide a detennination of the average crystallite domain size, assuming no lattice strain or defects, tlirough the Debye-Scherr fonnula ... 

Solvent Resistance. At temperatures below the melting of the crystallites, the parylenes resist all attempts to dissolve them. Although the solvents permeate the continuous amorphous phase, they are virtually excluded from the crystalline domains. Consequently, when a parylene film is exposed to a solvent a slight swelling is observed as the solvent invades the amorphous phase. In the thin films commonly encountered, equilibrium is reached fairly quickly, within minutes to hours. The change in thickness is conveniently and precisely measured by an interference technique. As indicated in Table 6, the best solvents, specifically those chemically most like the polymer (eg, aromatics such as xylene), cause a swelling of no more than 3%. 

The optical properties of tubular blown film depends greatly on the surface irregularities and the size of crystallites domain in film, which, in turn, are dependent on... 

The dissolution of zinc in a mineral acid is much faster when the zinc contains an admixture of copper. This is because the surface of the metal contains copper crystallites at which hydrogen evolution occurs with a much lower overpotential than at zinc (see Fig. 5.54C). The mixed potential is shifted to a more positive value, E mix, and the corrosion current increases. In this case the cathodic and anodic processes occur on separate surfaces. This phenomenon is termed corrosion of a chemically heterogeneous surface. In the solution an electric current flows between the cathodic and anodic domains which represent short-circuited electrodes of a galvanic cell. A. de la Rive assumed this to be the only kind of corrosion, calling these systems local cells. 

Zeolite structures sometimes remain unsolved for a long time, because of either their complexity, the minute size of the crystallites or the presence of defects or impurities. One extreme example of stacking disorder is provided by zeolite beta [1,2], Different stacking sequences give rise to two polymorphs (A and B) in zeolite beta that always coexist in very small domains in the same crystal. Not only do the small domains make the peaks in the powder X-ray diffraction pattern broad and thereby exacerbate the reflection overlap problem, but the presence of stacking faults also gives rise to other features in the diffraction pattern that further complicate structure solution. 

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