Crystallinity peak area

C.I Area of crystalline Peak / [Area of crystalline peak-r Area of amorphous peak]. 

The diffraction lines due to the crystalline phases in the samples are modeled using the unit cell symmetry and size, in order to determine the Bragg peak positions 0q. Peak intensities (peak areas) are calculated according to the structure factors Fo (which depend on the unit cell composition, the atomic positions and the thermal factors). Peak shapes are described by some profile functions 0(2fi—2fio) (usually pseudo-Voigt and Pearson VII). Effects due to instrumental aberrations, uniform strain and preferred orientations and anisotropic broadening can be taken into account. 

How much of a crystallizable material X can I blend uniformly into a polymer until it starts to form crystals A series of blends with increasing amount of X is prepared. The samples are studied by WAXS (cf. Sect. 8.2) using laboratory equipment. Crystalline reflections of X are observed, as X starts to crystallize. Peak areas can be plotted vs. the known concentration in order to determine the saturation limit. Think of X being Ibuprofen and Y a polystyrene-(7 )-polyisoprene copolymer, and you have an anti-rheumatism plaster. 

As with ceramics and metals, polymer crystals can have multiple crystal forms. Polyethylene has a metastable monoclinic form and a orthohexagonal high pressure form. A list of some of the more common polymers and their corresponding crystal strnctnres is given in Table 1.24. Finally, X-ray diffraction can be used to determine the amorphous to crystalline ratio in semicrystalUne polymers in much the same way that Eq. (1.61) can be used. Figure 1.66 shows a schematic illustration of the X-ray diffraction patterns for semicrystalline and amorphous polyethylene. The estimation of crystalline content is based upon a ratio of the peak areas in the two samples. 

The most common applications of DSC are to the melting process which, in principle, contains information on both the quality (temperature) and the quantity (peak area) of crystallinity in a polymer [3]. The property changes at Tm are often far more dramatic than those at Tg, particularly if the polymer is highly crystalline. These changes are characteristic of a thermodynamic first-order transition and include a heat of fusion and discontinuous changes in heat capacity, volume or density, refractive index, birefringence, and transparency [3,8], All of these may be used to determine Tm [8],... 

X-ray diffraction patterns from fibres generally contain a few closely overlapping peaks, each broadened by the contributions of crystallite size, crystallite-size distribution, and lattice distortion. In order to achieve complete characterisation of a fibre by X-ray methods, it is first necessary to separate the individual peaks, and then to separate the various profile-broadening contributions. Subsequently, we can obtain measures of crystallite size, lattice distortion and peak area crystallinity, to add to estimates of other characteristics obtained in complementary experiments. 

Typical results achieved with the crystalline cellulose I fibre, Ramie, and with the crystalline cellulose II fibre Fortisan, are illustrated in Figures 4 and 5 The 101, 10T and 002 profiles resolved by NUSOLVE G are given, together with the best-fit polynomial background. The parameters are listed in Table II, together with the total peak area expressed as a percentage. 

This latter parameter can be considered as the peak-area crystallinity within the two theta limits employed. 

Peak resolution is usually easier if well chosen background parameters are input and if constrained optimization methods are utilised. Misleading results can be obtained if the constraints are too limited and tests with unconstrained optimization are desirable if at all possible. In particular, the possible presence of paracrystalline or intermediate phase peaks must be tested with extreme care in order to avoid ambiguity. It is not sufficient to have a good mathematical resolution alone, all peaks must be significant in crystallographic or structural terms. The incidental measurement of peak-area crystallinity is considered to be of secondary importance to the resolution of overlapping peaks. 

Figure 11.3 Studies in mutant mice, (a) Image of mineral to matrix in the growth plate of a young mouse lacking matrix gla protein (MGP—/—) and its wildtype control (MGP+/+). Note the gradient of mineral matrix ratios in the wildtype is not apparent in the knockout, (b) Mineral matrix increases at three sites in the cortices of the osteocalcin knockout (KO) mouse (6 month data), while crystallinity is decreased relative to wildtype (WT) controls, (c) In the osteonectin knockout mouse (4 months old) the collagen maturity assessed in terms of the 1660 1690 peak area ratio is increased on the periosteal and endosteal surface.

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]

Enthalpy changes are derived from the peak areas of DSC curves taking the melting heat of DSP (12.0 kcal/mol) as a standard66. From the relative enthalpy levels of molten and crystalline DSP, and amorphous and crystalline poly-DSP, the topochemical photopolymerization of DSP is found to be an endothermal reaction with an enthalpy increase of about 3.7 kcal/mol. 

The CF4 plasma treatment yields F/C peak area ratio of approximately 1.5 for both cellulose and cellulose acetate films. When those surface-tagged films were immersed in liquid water, the fluorine atoms, which are detectable by XPS, decreases as a function of the immersion time. Figure 25.9 depicts change of F Is/C Is ratio as a function of immersion time in water, which shows that the disappearance rate of F Is peak is much higher for the semicrystalline cellulose film than that for the amorphous cellulose acetate film. These data actually compare the extent of X interaction rather than the degree of crystallinity, indicating that x interaction overwhelms the degree of crystallinity. 

The accuracy of the determination will depend upon the accuracy of peak areas used in the calculation, perhaps 2% - . For a crystalline complex, a single crystallization of material of >95% ee will almost certainly bring it to complete optical purity, in which case the absence of NMR signals for the minor diastereomer of the complex to within the limits of sensitivity of the NMR spectrometer will be the criterion for complete optical purity of the arsine. Since the displacement of an arsine from a configurationally homogeneous complex of this type is stereospecific with retention of configuration at arsenic and can be carried out under mild conditions, the arsine liberated will also be optically pure. However, to be certain of the optical purity of the arsine the diastereomer should be re-prepared on a small scale and checked once again for purity by NMR spectroscopy. 

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). ... 

XRD. Zeohtes were hydrated over saturated CaCh solution for 24 hours. Crystallinity of the powdered samples was determined by comparing peak areas (2-theta range from 10 to 35°) with those of the initial unsteamed zeohtes. X-ray spectra were collected using a Scintag diffractometer scanning at l°/min. 

WAXS is a powerful method of determining the degree of crystallinity. Since the scattering from the crystalline regions gives relatively sharp peaks compared to a broad hump due to scattering from non-crystalline areas (see Fig. 2.19), the degree of crystallinity can, in principle, be determined from the relative areas under the crystalline peaks and the amorphous hump. 

Figure 5. Crystalline melting peak area as a function of tin concentration...

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