Degree of crystallinity determination by X-rays

CA resonance line vs. degree of crystallinity determined by x-ray analysis. native cellulose, o regenerated cellulose,... 

Fig. 16. Integrated fraction of the downfield component of the C4 resonance line versus degree of crystallinity, /, determined by X-ray analysis., Native cellulose O, regenerated cellulose , mercerized cotton and ramie. (The data for regenerated cellulose samples, except for cupra rayon fibres, were reproduced from ref. 45).

In any case one speaks about the degree of crystallinity of the materials, being a measure of the volume fraction of the crystalline part of the material. This parameter is, however, not uniquely defined, but varies considerably with the method used for its determination. The degree of crystallinity determined by means of x-ray diffraction is often call the x-ray crystallinity, Xc- In the spirit of Ruland analysis [36]... 

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Polyester fibers contain crystalline as well as noncrystalline regions. The degree of crystallinity and molecular orientation are important in determining the tensile strength of the fiber (between 18-22 denier) and its shrinkage. The degree of crystallinity and molecular orientation can be determined by X-ray diffraction techniques. ... 

Since the Braggs first determination, thousands of structures, most of them far more complicated than that of sodium chloride, have been determined by x-ray diffraction. For covalently bonded low molecular weight species (such as benzene, iodine, or stannic chloride), it is often of interest to see just how the discrete molecules are packed together in the crystalline state, but the crystal structures affect the chemistry of such substances only to a minor degree. However, for most predominantly ionic compounds, for metals, and for a large number of substances in which atoms are covalently bound into chains, sheets, or three dimensional networks, their chemistry is very largely determined by the structure of the solid. 

Degree of Crystallinity as a Function of the Variety of Starch and the Partial Pressure of Water Vapor, as Determined by X-Ray Diffraction414... 

Electron diffraction from these crystals indicated a high degree of crystallinity in both the trimer and polymer, and indexing of the patterns required the use of new unit cells different from the usual structures(Figure 4). X-ray diffrac-tometry was used to provide structural information about the third dimension in these epitaxially crystallized films. It should be noted that the characteristic spacing determined by X-ray diffrac-tometry is the b-axis, only if the unit cell is orthorombic (Table II). 

The crystal lattice parameters observed for these copolymers by X-ray diffraction are found to be almost identical to those of the P(3HB) homopolymer. The degree of crystallinity determined from the X-ray diffraction decreases steeply from 60 to 23% as the 3HP content in the copolymers increases from 0 to 37 mol%. The trends of composition dependence of the thermal properties and the X-ray diffraction are very similar to those for P(3HB-co-4HB) but not to those for P(3HB-co-3HV), as already mentioned above. Thus, it is reasonable to assume that in the P(3HB-co-3HP) samples containing up to 37 mol% 3HP unit, the 3HB units exist in the crystalline as well as in the noncrystalline regions, while almost all of the 3HP units exist only in the latter. To further investigate this point, the NMR relaxation times have been measured for the films cast from a chloroform solution. 

The degree of crystallinity of a polymer reflects the relative amount of crystalline regions and of amorphous regions. This amount can be expressed on a volume or a mass basis. The degree of crystallinity is most accurately determined by X-ray scattering. In practice, this is a tedious operation and is rarely performed. 

Kline et al. [86,87] studied the MW dependence of the field-effect mobility in regio-regular poly(3-hexylthiophene) synthesized by different routes and prepared using different coating techniques. They found that the mobility universally increased with MW, while the degree of crystallinity as determined by X-ray diffraction considerably decreased. This... 

A comparison of the degree of crystallinity obtained by gas chromatography for poly(ethylene oxide) of molecular weight 40 000 with those determined by IE spectroscopy and X-ray diffraction yields [183] 74% for the first method when the polymer film thickness was 6.5 X10" cm, 75.9% for the second (film thickness 5.1X10 cm) and 79.1% for the last method. The differences were ascribed to the incomplete development of crystallinity in the films used in gas chromatography and IE s ctroscopy, these films being thinner than the diameter of the spherulites. 

X-ray powder diffractometry is widely used to determine the degree of crystallinity of pharmaceuticals. X-ray diffractometric methods were originally developed for determining the degree of crystallinity of polymers. Many polymers exhibit properties associated with both crystalline (e.g., evolution of latent heat on cooling from the melt) and noncrystalline (e.g., diffuse x-ray pattern) materials. This behavior can be explained by the two-state model, according to which polymeric materials consist of small but perfect crystalline regions (crystallites) that are embedded within a continuous matrix [25]. The x-ray methods implicitly assume the two-state model of crystallinity. 

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