Wide angle X-ray scattering
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Wide angle X-ray scattering (WAXS) is an X-ray diffraction technique that is often used to determine the crystalline structure of polymers. This technique specifically refers to the analysis of Bragg Peaks scattered to wide angles, which (by Bragg's law) implies that they are caused by small structures.
This term is often used in conjunction with the term Small angle X-ray scattering to characterize the type of scattering.
See also
Wide angle X-ray diffraction is a time-honored but some what out-of-favor technique for the determination of degrees of crystallinity of polymer samples. A diffraction technique for polycrystalline films where only crystallites diffract which are parallel to the substrate surface. The diffraction pattern generated allows to determine the chemical composition or phase composition of the film, the texture of the film (preferred alignment of crystallites), the crystallite size and presence of film stress. According to this method the sample is scanned in a wide angle X-ray goniometer, and the scattering intensity is plotted as a function of the 2θ angle. X ray diffraction is a non destructive method of characterization of solid materials. When X-rays are directed in solids they will scatter in predictable patterns based upon the internal structure of the solid. A crystalline solid consists of regularly spaced atoms (electrons) that can be described by imaginary planes. The distance between these planes is called the d-spacing. The intensity of the d-space pattern is directly proportional to the number of electrons (atoms) that are found in the imaginary planes. Every crystalline solid will have a unique pattern of d-spacings (known as the powder pattern), which is a “finger print” for that solid. In fact solids with the same chemical composition but different phases can be identified by their pattern of d-spacings.
This experiment is based on Bragg’s law
When X-rays hit an atom, they make the electronic cloud move as does any electromagnetic wave. The movements of these charges re-radiate waves with the same frequency (blurred slightly due to a variety of effects); this phenomenon is known as the Rayleigh scattering (or elastic scattering). These re-emitted X-rays interfere, giving constructive or destructive interferences; this is the diffraction phenomenon.
The interference is constructive when the phase shift is proportional to 2π; this condition can be expressed by Bragg's law:
Where • n is an integer, • λ is the wavelength of x-rays, and moving electrons, protons and neutrons, • d is the spacing between the planes in the atomic lattice, and • θ is the angle between the incident ray and the scattering planes
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