Nanoscale Organization of Fullerenes by Self-Assembly in a Diblock Copolymer Host Matrix

This study illustrates the principle of a novel route to organize C60 on the nanoscale. The method we propose uses the self-assembled structure of a host polystyrene-b-polyisoprene (PS-b-PI) copolymer as a scaffold to organize polystyrene stars with a C60 core, C60(PS) f (f = 2, 4, and 6). The effect of the molecular architecture of the stars (size of the PS arms and functionality f) on the microstructures formed in the blends with a symmetric PS-b-PI copolymer (30k/30k) has been investigated by transmission electron microscopy, differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The molar mass M w* and the functionality f of the stars are two key parameters that control their solubilization in the host copolymer matrix, hence, the microstructures and the C60 organization in the blends. Different regimes of solubilization have been identified as a function of the ratio M w*/M w PS between the molar mass of the stars and the PS block of the copolymer M w PS. Homogeneous and localized solubilization regimes are evidenced for C60(PS)6 stars with M w*/M w PS ≤ 0.35 and 0.6 ≤ M w*/M w PS ≤ 2, respectively. In the latter regime, the C60 cores are preferentially anchored in the middle of the PS lamellae. We also demonstrated that the star's functionality f, i.e., its compactness, controls the maximum molar mass of the stars at the solubilization limit in the blends: the higher the functionality of the stars, the higher the molar mass of stars that can be solubilized in the PS lamellae of a copolymer. The overall results are illustrated through different phase diagrams that visualize the required conditions to achieve the spatial organization of C60.