Does 1,8-Diiodooctane affect the aggregation state of PC71BM in solution?

1,8-Diiodooctane (DIO) is an additive used in the processing of organic photovoltaics and has previously been reported, on the basis of small-angle X-ray scattering (SAXS) measurements, to deflocculate nano-aggregates of [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in chlorobenzene. We have critically re-examined this finding in a series of scattering measurements using both X-rays and neutrons. With SAXS, we find that the form of the background solvent scattering is influenced by the presence of DIO, that there is substantial attenuation of the X-rays by the background solvent and that there appears to be beam-induced aggregation. All three factors call into question the suitability of SAXS for measurements on these samples. By contrast, SANS measurements, performed at concentrations of 15 mg ml21 up to and including 40 mg ml21, show no difference in the aggregation state for PC71BM in chlorobenzene with and without 3% DIO; we find PC71BM to be molecularly dissolved in all solve...