ABSTRACT
When a beam of radiation impinges on a sample, a portion of the radiation is scattered. This scattered fraction depends on both the nature of the radiation and the composition of the sample. The scattered ray becomes out of phase and they interfere. The amount of interference depends on scattering angle. The intensity of the scattering drops with increasing the scattering angle at a rate that depends upon particle size. For bigger particles, the rate of fall of intensity is greater. Different radiations like light, neutron and x-rays are used as sources for scattering studies. The wavelength ranges and thus the smallest structure that can be studied are:
Light : 2000 Å-10,000 Å
Neutrons : 0.1 Å-15 Å
X-ray : 0.5 Å-5 Å
All the scattering experiments have certain features in common. A radiation source provides a parallel monochromatic beam of radiation. It passes through the sample. A detector measures the scattered intensity as a function of scattering angle and Bragg’s angle. Small angle-scattering techniques are employed to measure, with sub-nm precision, pattern shape, dimensions and orientation for structures created in periodic arrays. Due to the nano-scale size of polymer crystallites, small-angle scattering is intense in semicrystalline polymers and a separate fi eld of analysis based on diffraction at angles below 6° is used to study the structure of polymers and fi bres.
