Wide-angle X-ray Scattering

Wide-angle X-ray scattering (WAXS) or wide-angle X-ray diffraction (WAXD) 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 sub-nanometer-sized structures.

Wide-angle X-ray scattering is the same technique as small-angle X-ray scattering (SAXS) only the distance from sample to the detector is shorter and thus diffraction maxima at larger angles are observed. Depending on the measurement instrument used it is possible to do WAXS and SAXS in a single run (small- and wide-angle scattering, SWAXS).

The technique is a time-honored but a somewhat out-of-favor technique for the determination of degree of crystallinity of polymer samples. 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.