Solution behavior of buckminsterfullerene (C60) in benzene

Solution characterization of buckminsterfullerene C60 in benzene was carried out by laser light scattering. Static and dynamic light scattering (SLS and DLS) experiments were accomplished by using an incident laser beam of 790 nm wavelength, and a fiber optic probe which was coupled to a RCA C31034 photomultiplier tube sensitive to the near ir wavelength. The effective hydrodynamic radius of C60 in benzene solution determined by using DLS was 6.4±0.1 Å, in close agreement with the distance measured from the center of the solvated benzene to the center of the benzene-solvated C60 (C60⋅4C6H6):6.7∼6.8 Å as evaluated from the single crystal structure by x-ray diffraction. C60 was found to aggregate slowly even in fairly dilute solution concentrations ranging from 0.78 to 1.39 mg/mL at temperatures 23∼27 °C. Based on the high specific refractive index increment of C60 in benzene, the molar mass of the C60 aggregates could be estimated. Together with the radius of gyration, the hydrodynamic radius, and its size distribution, the kinetics of the aggregation process was investigated. The aggregation of C60 in benzene solution was reversible, i.e., the C60 aggregates could be dispersed simply by hand shaking the solution. The light-scattering intensity results indicated that the structure of C60 aggregates could be described as a fractal with a dimension of 2.10 and the aggregation kinetics exhibited essentially an exponential behavior.