Spheres, rods, discs, which can fit what?

Table showing which model can be used to fit scattering patterns from a variety of polydisperse shapes.

A remark in a recent paper by Dr. Yojiro Oba (currently at KURRI) caught my attention. It discusses which shape assumption can be appropriate to fit a scattering pattern of polydisperse systems. In the paper, the shape assumption is spherical (based on TEM evidence), and a further remark goes as follows:

Since no qa (a < 4) behaviour is observed, the possibility of anisotropic shapes such as a rod, disc, and ellipsoid of revolution is denied.

That is an elegant way of putting it (note that it is an unidirectional exclusion and does not work the other way), and it sounds about right. So let’s test this with some simulations. These, of course, cannot prove that the statement is true, but can only disprove the statement. Read more »

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Applications of SAXS: Self-assembled Structures

Martin's Molecule

[Ed: It looks like there is more interest than I thought in the field of SAXS; the "Everything SAXS" review paper has been downloaded over 10000 times!]

One more application we found for small-angle scattering was to research structures molecules assemble in when immersed in liquids. Many of us are familiar with the micellar structures that appear in water-based solutions, but what happens in other solvents? Read more »

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