Abstract
Using small angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS), we have studied aqueous solutions of a fullerene-based star ionomer-hexa(sulfobutoxypentylcarboxy)[60]fullerene (FC 10 S). With six sulfobutoxypentyl arms randomly bounded on the C 60 cage, FC 10 S demonstrates a good solubility in water. The scattering results show that the water-soluble fullerene-based ionomers of a starlike molecular morphology form rodlike aggregates in water solutions. With the contrast provided by SAXS and SANS, we extract detailed structural information for the rodlike aggregates, including arm distribution, aggregation number ∼ 32, and the rod radius and length of 21 Å and 160 Å, respectively. We also extract an averaged ionization factor of ∼ 0.03 for the FC 10 S aggregates, using the structural factor derived from the mean spherical approximation model for the charge interacting aggregates. The aggregation structure changes little within the concentration range studied (0.5-4%). Compared to the aggregation characteristics of FC 4 S, a similar fullerene-based ionomer with six shorter sulfobutyl arms, FC 10 S, has a much higher aggregation tendency due to the longer sulfobutoxypentyl arms anchored on the C 60 cage.