Phenomena and processes related to the behavior of fullerenes in solutions are reviewed. Data on the solubility of C 60 and C 70 fullerenes in a large number of solvents at various temperatures are presented as well as on diffusion coefficient of fullerenes in solutions. The relation between the factors controlling the behavior of dissolved fullerenes and the clustering tendency they show is analyzed. This tendency, which sets fullerenes apart from other large molecules, underlies many aspects of fullerene behavior in solutions, such as the recently discovered nonmonotone temperature dependence of fullerene solubility in various solvents, the nonlinear concentration dependence of nonlinear optical susceptibility, the sharp dependence of the color of a fullerene solution on the solution composition (the solvatochromatic effect), the concentration dependence of the heat of solution of fullerenes in organic solvents, etc. Growth mechanisms of fractal clusters in fullerene solutions are analyzed along with similarity laws determining the thermodynamic characteristics of fullerite crystals.

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The phenomenon of formation of fractal cluster structures in fullerene solutions discovered in recent experiments is analyzed theoretically. As the basis for analysis the standard fractal cluster growth approach is used. The simplest approximation based on the supposed temporal independence of both fractal cluster dimensionality and attachment probability of two clusters does not provide agreement between the measured and calculated cluster growth data. A satisfactory agreement is attainable in a frame of the Reaction Limited Cluster Aggregation model in the supposition that the attachment probability γ depends on cluster size. The best fitting is obtained for the dependence γ = γ0(r0/R)α, where γ0 = 10−7, α = 2. The possible physical mechanism clarifying such a dependence is considered.

The diffusion of fullerenes in solution is studied taking into account the recently established formation of clusters containing numbers of aggregated fullerence molecules. Based on a droplet model of a cluster, the distribution function of fullerence clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters diminishes as the concentration decreases. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerence C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.

The phenomenon of the thermal diffusion of fullerenes in solutions concerned with the fact aggregation of fullerence molecules in clusters in organic solvents discovered recently is studied. The mechanism of this phenomenon based on the temperature dependence of the cluster size distribution function is proposed. The temperature and concentration dependencies of the cluster size distribution function calculated previously are used to calculate the thermal diffusion coefficient of C60 fullerene in toluene solution as a function of temperature and concentration. It is shown that the mechanism spoken of dominates in thermal diffusion at the temperature above the phase transition temperature in solid C60. A contribution of the conventional mechanism of thermal diffusion caused by a considerable difference in fullerene and solvent molecule dimensions is estimated.