The state of amorphous polymers by small-angle scattering

In this paper it is clarified that SANS and SANS (small-angle X-ray and neutron scattering, respectively) define two different RG'S (radii of gyration). SAXS describes the RG of the volume pervaded by a tagged macromolecule while SAXS determines the RG of a volume defined by density fluctuations. The fact that SAXS is observable is somewhat inconsistent with the extensive intermolecular interpenetrations implicit in the model of Gaussian segmental density distribution. The difference between the RG'S observed by SAXS and SANS is quite large and, at least for polystyrene, is maintained over a large molecular weight range. The dependence of the RG'S on molecular weight is similar for both SAXS and SANS. Additional information is obtained by studying the effects of molecular weight distribution with SAXS. The consistency of these data with possible models for the amorphous state is discussed.