Fraunhofer Institute for Structural Durability and System Reliability LBFX-ray Crystallography
X-Ray diffraction is the diffuse elastic scattering of monochromatic x-ray radiation by electrons in the examined samples. Conclusions about the structure of the sample can be drawn from the angle dependent intensity of the measured radiation.
The term “small angle x-ray scattering” (SAXS) describes the scattering by x-rays on a sample under small scattering angles (0.1° - 10°). In this range, structures of a size between 1 nm and 100 nm can be depicted. SAXS finds its application in the examination of characteristic structures of hierarchical materials, such as inhomogeneities, size and shape of macromolecules, morphologies and dynamic processes (for example melting process).
Many polymers are semi-crystalline two phase systems. The crystalline regions generally have a flat lamellar structure. The lamellae – thickness around 10 nm – are surrounded by amorphous material. The lamellae order themselves to spherical superstructures called spherulites. The respective morphology can be revealed excellently with x-ray scattering experiments. The crystal structure and the inner structure of the amorphous regions is determined by wide angle scattering, with a scattering angle higher than 3°, whereas the stacking of lamellae causes scattering at angles under 3° (small angle scattering).
Applications:
Wide angle X-ray analysis:
(with line focus: goniometer for one dimensional registration of scattering images)
- Identification of polymers and their crystal modifications
- Determination of the degree of crystallinity
- Determination of crystallite size
- Determination of internal mechanical stress
Wide angle X-ray analysis:
(with focus point, image plate camera for two dimensional registration of scattering images)
- Identification of polymers and their crystal modifications
- Qualitative texture analysis
Small angle X-ray analysis:
(with line focus: Kratky camera for one dimensional registration of scattering images)
- Determination of lamellae distance (“long periods” <50nm)
- Determination of size (<70nm) and size distribution of colloids, suspensions or (semi-crystalline) structures.
Small angle X-ray analysis:
- Determination of lamellae distance (“long periods” <50nm)
- Qualitative analysis of molecular superstructures