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X-ray scattering

In this laboratory X-ray diffraction is mainly used to investigate the crystalline phase in polymers. Broadly speaking, X-ray diffraction can be split into two categories, wide angle (WAXS), which considers scattering angles greater than ~5o, and small angle (SAXS), which is concerned with scattering angles less than this. With the appropriate x-ray wavelength these correspond to examining structures of dimensions several Angstroms, such as crystals, and hundreds of Angstroms, such as lamellae and more macroscopic features.

Typical information that can be obtained from WAXS includes:

  • Crystalline orientation in uniaxially and biaxially oriented samples
  • Crystallite size
  • Crystal strain in response to stress or temperature fields

Typical information that can be obtained from SAXS includes:

  • Long period
  • Particle size and shape

SAXS experiments are performed using a simple pinhole collimation system combined with an area detector. This allows anisotropic structures to be investigated and avoids the need for desmearing corrections associated with line sources. The wide dynamic range and high x- ray detection efficiency of the detector compensate for the low beam intensity associated with the collimation system.

The left side of this enclosure contains position sensitive detectors which can record intensity over a range of scattering angles. They are used to follow positional changes of diffraction peaks produced by applying a stress to a sample. Several specially designed extensometers allow measurements to be made on both equatorial and meridional reflections over a range of temperatures. This experiment gives information on the moduli of the crystal and, to some extent, the structure of the material. To the right is a high resolution 2-circle diffractometer, which can be used to study the breadth of diffraction profiles. This allows information concerning the crystallite size and crystal distortions to be obtained. It is also used to analyse flat multilayer metallic systems in reflection at both wide and small scattering angles.