Analysis of small-angle scattering data of interacting ellipsoids using pair distance distribution functions.

Pair distance distribution functions (PDDFs) similar to those obtained by indirect Fourier transformation of small-angle scattering data from interacting prolate and oblate ellipsoids have been simulated using a Monte Carlo approach. Interactions were modelled with a square-well or square-wall potential combined with a non-overlapping core, and spanned from a maximum attraction of -1.5 kT per pair of particles to a repulsion of +1.5 kT. Volume fractions ranged from 1% to 10%, with an extension to 20% for systems in which particles interacted solely via non-overlapping cores, without further attraction or repulsion. The data were also transformed into scattering curves and analysed using the generalized indirect Fourier transformation (GIFT). The results show that rules of thumb for interpreting PDDFs can be misleading. GIFT removes most interaction effects and allows correct identification of the ellipsoidal shape; however, axis lengths are often underestimated. Attractive interactions are more challenging than repulsive ones and may go unnoticed without additional information.