Crystallinity scattering

The relative degree of crystallinity can also be estimated from the WAXS pattern from the ratio of the integrated intensity of the crystal peak to that of the total amorphous and crystalline scattering (Balta-Calleja and Vonk 1989). For PE, the amorphous scattering below the (110) peak (Fig. 5.7) is relatively insensitive to the degree of crystallinity, so the integrated area of the (110) reflection compared to the broad amorphous halo is directly proportional to XPE. However, the absolute degree of crystallinity cannot be determined in this way (Ryan et al. 1995). 

Methods for estimating lattice distortion generally require two or more orders of a particular reflection to be present, and most polymers have only one order available. A method for estimating both crystallinity and lattice disorder, which does not need higher orders of a reflection, and indeed takes into account the whole of the diffraction trace, is that due to Buland (27). This method has been applied to many different fibres by Sotton and his colleagues, who have discussed their results both here (28) and elsewhere (12). The major problem with Ruland s method is that an arbitrary separation of the crystalline scatter from the non-crystalline scatter must be made other restrictions are that the method cannot be used to measure crystallite size and cannot give any indication of the presence of paracrystalline or intermediate-phase material. 

The residual difference after a successful DDM refinement or/and decomposition can be considered as a scattering component of the powder pattern free of Bragg diffraction. The separation of this component would facilitate the analysis of the amorphous fraction of the sample, the radial distribution function of the non-crystalline scatterers, the thermal diffuse scattering properties and other non-Bragg features of powder patterns. The background-independent profile treatment can be especially desirable in quantitative phase analysis when amorphous admixtures must be accounted for. Further extensions of DDM may involve Bayesian probability theory, which has been utilized efficiently in background estimation procedures and Rietveld refinement in the presence of impurities.DDM will also be useful at the initial steps of powder diffraction structure determination when the structure model is absent and the background line cannot be determined correctly. The direct space search methods of structure solution, in particular, may efficiently utilize DDM. 

BELL, J., SUMMIT an IBM 7090 program for the computation of crystalline Scattering Kernels, General Atomic Report GA-2492, (Feb. 1962). 

The authors suggested that experimental area of the crystalline scattering, F r, is proportional to crystallinity (Crl), while height of the amorphous area, h, is proportional to pantamorphia index... 

Conventional spontaneous Raman scattering is the oldest and most widely used of the Raman based spectroscopic methods. It has served as a standard teclmique for the study of molecular vibrational and rotational levels in gases, and for both intra- and inter-molecular excitations in liquids and solids. (For example, a high resolution study of the vibrons and phonons at low temperatures in crystalline benzene has just appeared [38].)... 

Recently, a unique approach for using the correlation fiinction method has been demonstrated to extract morphological variables in crystalline polymers from time-resolved syncluotron SAXS data. The principle of the calculation is based on two alternative expressions of Porod s law using the fonu of interference fiinction [33. 36]. This approach enables a continuous estimate of the Porod constant, corrections for liquid scattering... 

Broadening of spots can result from themial diffuse scattering and island fomiation, among other causes. The themial effects arise from the disorder in atomic positions as they vibrate around their equilibrium sites the sites themselves may be perfectly crystalline. 

Jen S, Clark N A, Pershan P S and Priestley E B 1977 Polarized Raman scattering of orientational order in uniaxial liquid crystalline phases J. Chem. Phys. 66 4635-61... 

Figure 4.7c illustrates how x-ray diffraction techniques can be applied to the problem of evaluating 6. If the intensity of scattered x-rays is monitored as a function of the angle of diffraction, a result like that shown in Fig. 4.7c is obtained. The sharp peak is associated with the crystalline diffraction, and the broad peak, with the amorphous contribution. If the area A under each of the peaks is measured, then... 

Figure 8.35 Interference between scattered pbotoelectrons in (a) a gaseous diatomic molecule and (b) a crystalline material...

The EXAFS technique is used primarily for investigations of disordered materials and amorphous solids. Figure 8.35(b) shows how interference occurs between the wave associated with a photoelectron generated on atom A and the waves scattered by nearest-neighbour atoms B in a crystalline material. 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

The ultraphosphates are situated between P O q and the metaphosphates. These comparatively Htde-known, highly cross-linked polymers contain at least some of the phosphoms atoms as triply coimected branching points. This stmctural feature is quite unstable toward hydrolysis. Ultraphosphates undergo rapid decomposition upon dissolution. In amorphous ultraphosphates, the cross-linking is presumably scattered randomly throughout the stmctural matrix in contrast, crystalline ultraphosphates have a regular pattern. 

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