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, C₆₀, 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 (<i>M</i>_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 (<i>R</i>_g^poly), hydrodynamic radius (<i>R</i>_h), and the mixture correlation length (ξ) remain unchanged upon addition of C₆₀. The miscibility of C₆₀ 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 <i>M</i>_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