Small-angle X-ray scattering (SAXS)
About this technique
Small-angle X-ray scattering (SAXS) is used to measures the elastic scattering from inhomogeneities within a material over an angular range of approximately 0.05–5°. These scattering profiles can be used to determine information about the sizes and shapes of, and the distance and nature of the interactions between, these inhomogeneities. The ranges of sizes or distances that can be determined are typically on the order of a few to tens of nanometres and the samples can be liquid or solid in nature. It must be noted however, that the data generated by SAXS are averaged across the sample. This technique does not give an image showing specific pores or particles as do some other techniques. Nevertheless it can be very valuable in providing information about non-crystalline materials.
Typical examples of the types of information that can be determined include measurements of: the size and shape of nanoparticles, polymers, proteins or micelles in solution; measurements of pore size and interpore spacing in mesoporous materials; characteristic length scales in partially ordered systems, e.g. block copolymers, composites and gels; and interparticle interactions in colloidal dispersions. Hence SAXS has many applications in the fields of structural biology, chemistry, physics and engineering and sample types: e.g. polymers, pharmaceuticals, cosmetics, foods, catalysts, coal, membranes, and proteins.
The SAXS instrument is equipped with both CCD and image plate detection. The system uses a sealed X-ray tube and a Kratky camera (i.e. line collimation) which allows for the detection of dilute or weakly scattering systems. However the systems must be isotropic in nature (i.e. non-oriented). Measurements can be made of a variety of sample types including liquid dispersions, films, gels and finely ground powders over a range of temperature; approximately -20–100°C, depending on the nature of the sample.