Ultrasonic Formation of Highly Concentrated Aqueous Dispersion of Fullerene-Polymer Nanoparticles by Charge Transfer

Fullerenes attract much interest due to the potentials to various applications. However, their insolubility in water and some organic solvents often hinders development. Herein, poly(ethylene glycol) (PEG), polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), polyacrylic acid (PAA), and Pluronic L64 and 17R4, are attempted for dispersing fullerene in water via ultrasonication, and some of these are found to disperse an exceedingly large amount. The maximum concentration of C₆₀ is achieved with Pluronic L64, being 9.8 g/L (13.6 mm) without re-aggregation for a long time. Electron paramagnetic resonance (EPR) spectroscopy shows a significant amount of radical species existing in the fullerene-polymer complexes, which are stable for several weeks. DLS and TEM exhibit the formation of nanoparticles, and NMR, FT-IR, and MALDI-TOF MS are used to characterize the fullerene nanoparticles-polymer complexes. The aqueous dispersions of the complexes can be dried and redispersed in water and polar organic solvents. Column chromatographic separation is performed to give unreacted fullerene and fullerene-polymer complexes, the latter of which shows a strong EPR signal. Density functional simulations reveal partial electron transfer from the PEG segment to fullerene, which causes charge separation in the complexes, resulting in the excellent dispersibility in water, while the poly(propylene glycol) (PPG) segment likely assists the complexation by hydrophobic interactions with fullerene.