Evidence for C<inf>60</inf> aggregation from solvent effects in [Ps-C <inf>60</inf>] molecular complex formation

Using a molecular probe positronium (Ps), Ps reaction rate constants (k) with C60, a strong Ps acceptor, are determined for the formation of a donor-acceptor type molecular complex in solvents of varying surface tension (σ) and viscosity (η). Within the framework of Smoluchowski's theory of diffusion, the calculated Stokes radius for C60 in the different solvents deviated from the monomeric value, implying the existence of aggregated clusters in solution and using transmission electron microscopy, C60 aggregation in carbon disulphide (CS2) is observed with the formation of spherical fractal clusters of ̃90 nm size with aggregation number 1.7 × 104 and a fractal dimension of 1.9 at a concentration of 0.5 mM. The fractal dimension of 1.9 revealed the mechanism of aggregation to proceed through a diffusion limited process with the estimated diffusion coefficient and the diffusion length of the aggregated cluster to be 2.27 × 10-6 cm2/s and 0.63 nm, respectively. © 2003 Elsevier Ltd. All rights reserved.