Small-angle X-ray scattering

Small-angle X-ray scattering (SAXS)

SAXS is a technique that is used for the structural characterization of solid and fluid materials in the nanometer (nm) range. It probes inhomogeneities of the electron density on a length scale of typically 1-100 nm, thus yielding complementary structural information to XRD (WAXS) data. It is applicable to crystalline and amorphous materials alike.

Measurements are commonly performed in a transmission geometry, using a narrow, well-collimated and intense X-ray beam. Scattering angles typically range between 0.1 and 5 deg. The smallest accessible angle determines the largest resolvable feature size. Samples can be easily prepared and are measured either in a capillary, as a thin layer between polymer foils, or free-standing.

Some typical applications comprise the determination of nanoparticle and pore size distributions, of specific surface areas and the structure analysis in inhomogeneous (e.g. core-shell) particles. The technique may also yield information with respect to the aggregation behavior of nanoparticles. Furthermore, SAXS is applied for analyzing structures in colloids, membranes, liquid crystals, detergents, microemulsions, polymers etc. Under the condition that all particles essentially have the same size, it is possible to determine their shape and internal structure. As an example, SAXS is used to analyze the envelope shape of proteins and or other biomacromolecules in dilute solution.

The measurement time on a laboratory instrument may range from a few minutes up to several hours. It depends on the type of instrument and optics used, on the sample concentration and on the electron density contrast. An evacuated beam path helps in reducing the effects of air scattering and in speeding up the measurements. However, even on a multi-purpose diffractometer in air, high-quality SAXS data can often be obtained for a large variety of samples.

PANalytical solutions for small-angle X-ray scattering

Instrumentation
PANalytical's Empyrean multi-purpose diffractometer system allows for SAXS measurements on solids, powders and liquids using a large variety of optical configurations and sample stages. All optical components and sample stages are pre-aligned (PreFIX) allowing to change from one configuration to any other within just a few minutes. An automatic sample changer allows to perform automated measurements in a batch mode.

Software
EasySAXS is a stand-alone, easy-to-use software package for the automated analysis of SAXS data from samples containing nanoparticles (such as nanopowders, nanoparticle dispersions and nanocomposites) and from porous materials. It reads in experimental data files, performs background-correction, estimates particle / pore size distributions, and the surface-to-volume ratio of spherical particles.