Crystalline peak

It is important to note that expression (23) can be applied to the crystalline phase intensities only if we include, in the first integral, its own smooth diffuse background and not just the intensity belonging to the crystalline peaks. In fact, a pure crystalline sample also has a smooth background due to the incoherent inelastic scattering (i.e. Compton scattering), the TDS, disorder scattering and, very often, unresolved tails of overlapped peaks. 

Figure 5.5. Raman spectroscopy of laser crystallized solution-processed silicon films. The plot shows laser intensity versus Raman shift of the film. The crystallinity is estimated from the intensity and width of the crystalline peak at 520 cm-1. [Reproduced with permission from Ref. 11. Copyright 2006 The Japan Society of Applied Physics.]...

The experimental spectra for (SiMe2) at selected temperatures are shown in Figure 32. The growth with temperature of a feature slightly upfield from the low-temperature crystalline peak is thus evidence for existence of deviant-turns within a predominantly ////-conformation. 

X-ray measurements also indicate photocrystallization at exposure values E > Typical results, i.e., X-ray diffraction patterns of photocrystallized samples (this stage refers to curve 5 of Fig. 7.11), show four crystalline peaks located at 29 = 24°, 30°, 41°, and 45°. These can be indexed as 100, 101, 110, and 111 of the hexagonal Se crystal, respectively. Similar X-ray diffraction patterns were obtained by Ishida and Tanaka [26] examining photoinduced birefringence in a-Se thin films. 

DEAE-cellulose column was further purified on Sephadex G-200 but resisted all efforts at crystallization. Figure 14 (4) shows the polyacrylamide gel electrophoretic pattern of crude rat liver extract with two bands, the resolution of these bands by DEAE-cellulose, and the crystalline peak I preparation. The crystalline enzyme had an approximate molecular weight of 100,000 estimated by sucrose density gradient... 

We will now consider three cases where satisfactory peak resolution was much more difficult to achieve. Case (a), a specimen of PET fibre used for texturising, having poorly defined crystalline peaks and possibly an additional peak due to an intermediate phase (11) case (b), a specimen from a range of PET fibres with different shrinkages (.12.), again an additional intermediate phase peak was a possibility case (c), cold drawn polypropylene fibres (13). an additional paracrystalline peak was most likely here. 

Because of the possibility that an intermediate phase exists in PET, see Case (b), the resolution was carried out with four peaks and zero background parameters. Eventually, and only after several attempts, a good fit was found with three crystalline peaks, one very broad noncrystalline peak, and a polynomial background. On adding the broad peak to the new background, an identical result to that of Figure 6 (Table III) was obtained, casting doubt on the existence of a true intermediate phase. 

Figure 7. Crystalline peak resolution. Corrected and smoothed equatorial trace of a PET fiber specimen resolved into three crystalline peaks, 010, 110, 100, and...

Resolution of polyester specimen PET 06 into three crystalline peaks, and three crystalline peaks and a paracrystalline peak... 

Figure 11. Good resolution with constrained optimization and addition of a paracrystalline peak. Corrected equatorial trace of a polypropylene fiber specimen cold drawn X-5.5. Total theoretical trace now comprised of realistic crystalline peaks 110, 040, 130, 111, 131, 041, and paracrystalline peak at 15.5°. Compare...

Nevertheless, when we carry out x-ray crystallinity measurements on textile fibers, we must consider distortions that always affect crystalline material. Even in a completely crystalline material, the scattered x-ray intensity is not located exclusively in the diffraction peaks. That is because the atoms move away from their ideal positions, owing to thermal motion and distortions. Therefore, some of scattered x-rays are distributed over reciprocal space. Because of this distribution, determinations of crystallinity that separate crystalline peaks and background lead to an underestimation of the crystalline fraction of the polymer. In this paper, we attempt to calculate the real crystallinity for textile fibers from apparent values measured on the x-ray pattern. This is done by taking into account the factor of disorder following Ruland s method (3). 

Finally, before carrying out the calculation, it is necessary to sketch the boundary between the crystalline peaks and the amorphous background. This line can be calculated if an amorphous sample has been used as a reference, such as for PET and cellulose fibers. If no amorphous standards are available, the background is drawn manually, following a line parallel to the theoretical curve (jt,5) (total scattering power summing up coherent and incoherent scattering). 

Another method is based on the intensity of X-ray diffraction as a function of the diffraction angle 0 the ratio of the areas of the crystalline peaks and the amorphous background gives [Pg.79]

Figure 12.14. Dependence of the crystalline peak of PDMS on the amount of carbon nanotubes. [Reproduced by permission of Kautschuk Gummi Kunststoffe from L. Bokobza and M. Rahmani "Carbon nanotubes Exceptional reinforcing fillers for silicone rubbers", KGK, 62,112,2009],...

Mixtures of crystalline and amorphous forms were also quantitated in a similar manner, but by using deconvolution to calculate peak areas due to overlap between the broad amorphous peaks and the narrow crystalline peaks (Fig. 4). The NMR quantitation first seemed to disagree with the calculated weight percent (Table 2), but on further investigation, the authors discovered amorphous impurities in the crystalline standards, and when these amorphous components were corrected for, the NMR quantitation agreed very well with the calculated weight percent (Table 3). ... 

FIGURE 3.12. WAXD patterns of Alq3 as it is annealed at 145°C. The initial amorphous hump resolves rapidly into crystalline peaks. 

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