Aggregation and Deposition Kinetics of Fullerene (C₆₀) Nanoparticles

Abstract

The aggregation and deposition kinetics of fullerene C60 nanoparticles have been investigated over a wide range of monovalent and divalent electrolyte concentrations by employing time-resolved dynamic light scattering (DLS) and quartz crystal microbalance (QCM), respectively. Aggregation kinetics of the fullerene nanoparticles exhibited reaction-limited (slow) and diffusion-limited (fast) regimes in the presence of both electrolytes, having critical coagulation concentrations (CCC) of 120 and 4.8 mM for the monovalent (NaCl) and divalent (CaCl2) salts, respectively. The measured stability ratios of the aggregating fullerene nanoparticles were in very good agreement with Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, with a derived Hamaker constant of 6.7 x 10-21 J for the fullerene nanoparticles in aqueous medium. For the deposition kinetics studies, the rate of fullerene nanoparticle deposition increased with increasing electrolyte concentrations, as was indicated in the aggregation kinetics results. However, at electrolyte concentrations approaching or exceeding the CCC, the rate of deposition dropped sharply due to significant concurrent aggregation of the fullerene nanoparticles. The deposition of the fullerene nanoparticles was further shown to be mostly irreversible, with immediate detachment of the nanoparticles observed only when exposed to a solution of high pH.

Towards better understanding of C60organosols

“…Third, the striking decrease in CCCs in the non-aqueous solvent was fixed: for Na + and other single-charged cations, this value was three orders of magnitude lower as compared with those in water. 14,[18][19][20] Let us consider these issues step by step.…”

“…The numerous and sometimes conflicting results of experimental 5,14,[16][17][18][19][20][21][22][23][24][25][43][44][45][46][47][48][49] and theoretical [73][74][75][76][77][78][79] investigations demand such a comparison. Indeed, the theoretical calculations often predict strong interaction between C 60 and water (as a recent example, the work by Choi et al 77 may be proposed), which may be considered as a type of expressed hydration, whereas the coagulation data indicate the hydrophobic nature of the fullerene hydrosols.…”

“…16,17 Elimelech and his co-workers also reported less negative z values of C 60 hydrosols with CaCl 2 as compared with those in NaCl or KCl solutions, but no re-charging was registered. [18][19][20] It is therefore expected that further study of the coagulation of C 60 colloids in various polar organic solvents will provide insight into the nature of both organosols and hydrosols.…”

“…[8][9][10][11][12][13][14] While in low-polar aromatic solvents, fullerenes are well solvated and relatively well dissolved, 14,15 in water they generate hydrosols and suspensions. 5,11,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] In highly polar organic solvents, the molecular solubility of fullerenes is negligible, 14,15 but they readily form colloidal solutions. [9][10][11][12][13][14][31][32][33][34][35] The state of fullerenes, either molecular or colloidal, in the so-called 'good' or 'strong' solvents, such as CS 2 , toluene, and benzene, is still a matter of discussion.…”

“…9,[11][12][13][14][31][32][33][34][35] Typical examples are aggregates in N-methylpyrrolidin-2-one-acetonitrile mixed solvent, 3 toluene (benzene) mixtures with acetonitrile, 9,12,36 N-methylpyrrolidin-2-one 11,33 and other polar solvents, 13 DMSO, 31 acetonitrile, acetone, ethanol, methanol, and other polar solvents. 32,35,42 Though the stability and coagulation of aqueous C 60 colloids via electrolytes has been examined in full, 14,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][43][44][45][46][47][48][49] the corresponding research for organosols is absent to the best of the authors knowledge. Despite numerous publications describing the preparation procedure, particle size and other properties, the coagulation by electrolytes and the origin of the charge of colloidal species in organic solvents yet stays almost unexplored.…”