Colloidal dispersions of fullerene C60 in water:: some properties and regularities of coagulation by electrolytes

The ultramicroheterogeneous dispersion of buckminsterfullerene, C-60, in water was found to be a typical hydrophobic colloidal system. The studied sol was polydisperse (d from several nanometers to ca. 200 nm), with negatively charged surfaces of the particles. The coagulation by inorganic electrolytes occurs in accordance with the Schulze-Hardy rule; the reciprocal coagulation points for counter-ion charges z = 1, 2 and 3 are related as approximate to 1 :20:1500. The results are discussed in terms of the Derjaguin-Landau-Verwey-Overbeek theory. In the case of organic electrolytes, including colloidal cationic surfactants, their coagulation points decrease with increasing hydrophobicity and surface activity of the cations. An excess of cetyltrimethylammonium bromide stabilises the fullerene dispersion. The coagulating action of the tetrabutylammonium ion depends on the nature of the co-ion. Polyvinyl pyrrolidone and sodium dodecyl sulfate protect the C-60 sol from coagulation.