Conformation and Interactions of Polystyrene and Fullerenes in Dilute to Semidilute Solutions

We report the polymer conformation and fullerene aggregation in a ternary system containing polystyrene, C-60, and toluene measured by small angle neutron, static, and dynamic light scattering. We investigate polymer concentrations across the dilute and semidilute regime for five polymer molecular weights (M-w = 20 kg/mol to 1 Mg/mol), and fullerene concentrations below and above its miscibility threshold in toluene. We find that the polymer radius of gyration (R-g(poly)), hydrodynamic radius (R-h), and the mixture correlation length (xi) remain unchanged upon addition of C-60. The miscibility of C-60 in toluene, however, decreases upon addition of polystyrene forming aggregates with a time-dependent radius on the order of 100 nm, and this effect is amplified with increasing polymer M-w. Our findings are relevant to the solution processing of organic photovoltaics, which generally require the effective solubilization of fullerene derivatives and polymer pairs in this concentration range.