Colloid Chemistry of Fullerene Solutions: Aggregation and Coagulation

This review article is devoted to the colloidal properties of fullerene solutions. According to generally accepted understandings, all solvents in relations to fullerenes are divided into “good”, “poor”, and “reactive”. We have consistently considered the state of fullerenes in these systems. In “good”, predominantly non-polar aromatic solvents and CS2, non-equilibrium dissolution methods lead to the formation of colloidal aggregates, whereas the utilization of equilibrium methods results in the formation of molecular solutions. The latter, however, have some unusual properties; new results considered in this review confirm previously expressed ideas about colloidal properties of these solutions. In “poor” (polar) solvents, lyophobic colloidal systems appear. Both “bottom-up” and “top-down” methods of preparation are well documented in the literature. However, N-methylpyrrolidine-2-one, DMSO, and DMF dissolve fullerenes quite easily and with less energy consumption. These solvents can be considered a subset of “poor” solvents that have some features of being “reactive” at the expense of basic properties. New data confirm that hydrosols of fullerenes are typical hydrophobic colloids that obey the Schulze–Hardy rule and other regularities in the presence of electrolytes. Organosols in acetonitrile and methanol are much less stable with respect to the effects of electrolytes. This allows us to assume a non-DLVO stabilizing factor in the hydrosols. Accordingly, a new estimate of the Hamaker constant of fullerene–fullerene interaction is proposed. In DMSO and DMF, the coagulation of fullerene sols is hindered due to strong solvation with these basic solvents

Cluster-cluster interaction in nanodiamond hydrosols by small-angle scattering

The structure and interaction of nanodiamond fractal clusters were studied by small-angle X-ray and neutron scattering including contrast variation. The density of nanodiamonds, the aggregation number, and the ratio of aggregated/non-aggregated particles were determined. The analysis of the structure-factor made it possible to obtain the effective potential of cluster–cluster interaction. Branched fractal colloids behave to a certain extent like hard spheres, but the effective correlation length decreases with increasing concentration up to the sol–gel transition. The proposed approach for analyzing cluster–cluster correlations can be used in wider class of liquid systems with nano-sized non-compact inclusions

Diluted and concentrated organosols of fullerene C 60 in the toluene–acetonitrile solvent system as studied by diverse experimental methods

In this article, we examined the state of fullerene C$_{60}$ in toluene and its mixtures with acetonitrile in both diluted, (4.0 to 6.3)×10$^{−6}$ M, and concentrated, (0.23 to 1.9)×10$^{−3}$ М solutions, prepared by either equilibrium or non-equilibrium procedures. Typically, the working solutions were prepared by diluting stock solutions of fullerene in toluene. Some specific features of solid fullerene interaction with atmospheric oxygen were revealed using the LDI mass-spectrometry. A combination of electron absorption spectra of the fullerene in C$_6$H$_5$CH$_3$–CH$_3$CN mixtures with the analysis of the particle size distribution using the DLS method demonstrated that even in acetonitrile-rich media, where diluted C$_{60}$ exists in colloidal state, some features of the molecular absorption spectra are still present. Such effect is in line with the formation of the large solvation shells of an aromatic solvent around fullerenes. The TEM images of the dried colloidal solutions demonstrate a loose floc configuration of the aggregates, contrary to the crystal structure of the species in a toluene-free C$_{60}$ dispersion obtained by hand-grinding. In solution, the spectrum of the last-named is a monotonous curve increasing toward ultraviolet. The LDI measurements proved the tendency of C$_{60}$ toward forming negative species under contact with acetonitrile. Electrophoretic studies state that a universal property of the negatively charged colloidal species is their expressed ability to overcharging in the presence of inorganic cations, which are poorly solvated by acetonitrile. In concentrated (oversaturated) fullerene solutions, where the SAXS and SANS methods are applicable, fractal-type aggregates of fullerenes were revealed in solutions. The analysis of aggregates structure indicates that their packing density is increased with growth of fullerene concentration and/or amount of acetonitrile in the mixture. Thus, branched aggregates were observed in toluene solution, while fullerenes form dense clusters with diffusive surface in mixtures with acetonitrile