Supramolecular complex of [60]Fullerene-Grafted polyelectrolyte and surfactant: Mechanism and nanostructures

Water-soluble, pH-responsive mono- and di-[60]fullerene end-capped poly(acrylic acid)s (PAA-C-60 and C(60)PAA-C-60) were synthesized using the atom transfer radical polymerization technique. Isothermal titration calorimetry, dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy were employed to study the supramolecular complexation between fullerene end-capped PAAs and nonionic surfactant, polyethylene glycol (9-10) tert-octylphenyl ether, also known as Triton X100 TX100) at different pH values. At pH < 4, TX100 bound specifically to C-60 domains driven by hydrophobic and pi-pi interactions between TX100 and fullerene molecules. The binding was exothermic, and the magnitude of the interaction decreased gradually with increasing pH. The amount of polymer-bound TX100 was proportional to the fullerene content, which was similar to 1.3 and similar to 2.5 mM for 5 mM (concentration of carboxylic groups) PAA-C-60 and C-60-PAA-C-60, respectively. Morphological transformations resulting in the formation of polymer/surfactant complex (PSC) precipitates in the course of binding were observed for both polymers. The PSC of PAA-C-60 possessed a dense spherical structure, whereas the PSC Of C-60-PAA-C-60 possessed a lamellar stacking structure. The PSC precipitates resolubilized in excess amounts of TX 100 to form stable aggregates.