Surface Activity and Aggregation Behavior of Polyhydroxylated Fullerenes in Aqueous Solutions

Abstract

Polyhydroxylated fullerene (PHF) surface activity and aggregation behavior at the air−water interface were examined using surface tension and resonance-enhanced second harmonic generation (SHG). Surface tension data showed that PHFs are surface active with a limiting surface excess corresponding to 130 Å 2 /molecule in aqueous (Millipore water) solutions. Increasing the solution-phase ionic strength (through the addition of NaCl) reduces the PHF surface excess. Conductivity measurements show that PHFs carry a single charge, presumably negative. Surfacespecific SHG experiments show a small but measurable fixed wavelength, nonlinear response from solutions having surface excess coverages as low as ∼400 Å 2 /molecule. The SHG response of PHF solutions in the low-concentration limit shows unexpected behavior, implying that at bulk concentrations below 0.06 mg/mL, PHF monomers adsorb to the surface and interfere destructively with the intrinsic nonlinear susceptibility of the aqueous/vapor interface, leading to a ∼75% reduction in the SH signal. Above a PHF concentration of 0.0.06 mg/mL, the SH signal begins to rise in the Millipore and 50 mM NaCl solutions but remains very low in the 500 mM NaCl solutions. From this behavior, we infer that an increased nonlinear optical response is due to adsorbed aggregates.

The Effect of Different Substances Embedded in Fullerene Cavity on Surfactant Self-Assembly Behavior through Molecular Dynamics Simulation

“…Fullerene derivatives, as new amphiphilic surfactants, have been shown, in refs. [14][15][16], to have widely adjustable assembly behavior, shape, and function, compared with traditional amphiphilic surfactants. After the discovery by Sawamura [17] and Matsuo [18] that regioselective multiple addition reactions of organocopper reagents with C 60 can efficiently produce pentaphenyl adduct [19], new conical fullerene amphiphiles (CFAs) have gained increasing attention and have opened up a new dimension of amphiphile studies.…”