Interactions of Nanosized Aggregates of Fullerene C₆₀ with Electrolytes in Methanol: Coagulation and Overcharging of Particles

Abstract

Contrary to numerous studies on the stability of fullerene aqueous colloidal solutions in the presence of electrolytes, the corresponding issue for the organosols was until recently almost unexplored. In this article, the state of C in methyl alcohol and the regularities of the coagulation of colloidal solution in this solvent were examined in the presence of electrolytes. Alcosols with a fullerene concentration of 4 × 10 M were prepared by the dilution of the C saturated solution in toluene by methanol. The ca. 300 nm-sized aggregates possess a negative electrokinetic potential value, ζ = -37 ± 8 mV. To determine the critical coagulation concentrations, CCC, the size increase of the species was followed up using the dynamic light scattering method. The analysis of the coagulation in terms of the Fuchs function, W, was accompanied by zeta potential monitoring. The consideration of the data for 1:1 electrolytes NaClO and N(n-CH)ClO allows a rough estimate of the Hamaker constant of fullerene-fullerene attraction. Whereas in the case of these two electrolytes the colloidal species are negatively charged at the CCC, expressed overcharging of up to ζ = +36 mV by H, Ca, Ba, and La ions was observed. The action of HClO should be attributed to the interfacial acid-base reaction, whereas the excessive attraction of metal cations is caused by poor solvation in methanol; the negative charge is restored when the metal cations are shielded by a macrocyclic ligand.

Formation, Stability, and Coagulation of Fullerene Organosols: C70 in Acetonitrile–Toluene Solutions and Related Systems

“…Our studies on C 70 and C 60 fullerenes demonstrated that the critical composition of the binary solvent, which corresponds to the appearance of colloidal aggregates, depends on the fullerene working concentration. 22,37 Therefore, some discrepancies are observed between the results by different authors. 34,36,37 In Figure 1, such a critical composition corresponds to 38 vol % toluene.…”

“…Even for the most popular fullerene C 60 , such studies are few in number and probably originate only from this laboratory. 7,14,15 This is in stark contrast to the situation for aqueous suspensions and sols of fullerenes, for which coagulation via electrolytes has been studied in detail by many authors. 23−25 Meanwhile, besides elucidation of the stability conditions, such studies allow for evaluation of the Hamaker constant of the fullerene−fullerene interaction in vacuum.…”

“…1−6 In such liquid media, fullerenes are considered to be in a molecular state. On the other hand, fullerenes readily form colloidal species in polar solvents, such as methanol, 7,8 ethanol, 9−11 acetonitrile, 12−16 acetone, 11,16 Nmethylpyrrolidine-2-one, 17−21 etc. 5,17 The most popular method of preparation of colloids is the dilution of a stock solution in a "good" solvent, as concentrated as possible, by a polar solvent.…”

“…As a rule, the particle size is about 100−200 nm, and the electrokinetic potential is substantially negative. 5,7,11,[14][15][16]21,22 Such studies were performed not only for C 60 but also for C 70 . 5,11,12,21 However, to the best of the authors' knowledge, the stability of such organosols of C 70 against electrolytes has not been previously investigated.…”

“…23−25 Meanwhile, besides elucidation of the stability conditions, such studies allow for evaluation of the Hamaker constant of the fullerene−fullerene interaction in vacuum. 7,14,15,23,24 This constant is, in turn, a key parameter for understanding the properties and predicting the behavior and fate of these nanocarbon structures in a variety of liquid media. Therefore, our present research was devoted to the coagulation of C 70 sol by electrolytes in mixed toluene− acetonitrile solvent systems with a high content of CH 3 CN.…”