Principle of small-angle scattering

Nevertheless, small-angle scattering techniques are not very suitable for the study of lower dendrimer generations because such dendrimers yield only weak scattering signals and a high uncertainty factor therefore exists. SANS and SAXS experiments are not only costly, but also make substantial demands on time and require relatively large amounts of substances (several 100 mg). These methods are therefore out of the question for routine use, such as for the determination of the molar mass of dendrimers. 

One particular strength of SANS over SAXS is the differing scattering behaviour of isotopes towards neutrons, which is particularly pronounced for the hydrogen isotopes H and D. The true value of the SANS technique for structure analysis of dendrimers is due to this phenomenon. Thus, by deuterium label- 

Variation of contrast [46] is an important experimental technique in neutron small-angle scattering. Above and beyond size determination, it affords detailed insights into the internal structure of dissolved dendrimers and even permits the location of selected components of the molecule which have been previously labelled with deuterium. 

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The principle of small angle-scattering is to create regions of different mean coherent scattering density in the heterophase liquid. Since the measurements are at low Q-values, the scattered intensity is not influenced by the detailed molecular structure but depends on the average scattering length density, p which may be written as... 

The basic theory of small-angle scattering has been reviewed elsewhere [1,2] and only a short digest of fundamental principles will be reproduced here. The intensity of coherent scattering from an assembly of scatterers may be written as... 

Brunner-Popela, J. and Glatter, O. (1997). Small-angle scattering of interacting particles. 1. Basic principles of a global evaluation technique. J. Appl. Crystallogr., 30,431-442. 

This has to be borne in mind throughout the present chapter which will be concerned primarily with the static picture of lipoproteins, that is, their time-average structural principles. Much of this information has come from X-ray and neutron small-angle scattering on lipoprotein solutions and therefore, these techniques and their pertinent results will be discussed in some detail. For the interested reader, a brief recollection of the principles of the small-angle scattering method will be presented first, which... 

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