Concentration dependent response to pH modification and salt addition of polymeric dispersions of C₆₀ fullerenes

Diblockopolymers containing the pH-responsive monomer 2-(diethylaminoethyl) methacrylate (DEAEMA) were synthesized via RAFT polymerization. cryo-TEM imaging revealed the formation of micelles that were used for dispersion of C60 fullerenes in native pH, and their responsiveness to pH modification and salt addition was monitored at different concentrations. Concentration-dependent responsiveness was observed: Just above the CMC in native pH, pH reduction results in precipitation (release) of pre-dispersed C60. At high polymer concentrations the C60 dispersions are non-responsive. Dispersions of Carbon Black, a colloidal particle of much larger diameter, characterized as a reference system, showed a different nanomorphology and were not responsive to pH modifications, due to a different dispersion mechanism. We concluded that good size matching between the dispersed particles is necessary for the formation of micelle-entrapped dispersions, and that the responsivity of the C60 dispersion to pH reduction is limited to a concentration range between the CMC in native conditions and the CMC in acidic conditions.