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

Abstract

Using a molecular probe positronium (Ps), Ps reaction rate constants (k) with C-60, a strong Ps acceptor, are determined for the formation of a donor-acceptor type molecular complex in solvents of varying surface tension (sigma) and viscosity (eta). Within the framework of Smoluchowski's theory of diffusion, the calculated Stokes radius for C-60 in the different solvents deviated from the monomeric value, implying the existence of aggregated clusters in solution and using transmission electron microscopy, C-60 aggregation in carbon disulphide (CS2) is observed with the formation of spherical fractal clusters of similar to90 nm size with aggregation number 1.7 x 10(4) 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 x 10(-6) cm(2)/s and 0.63 nm, respectively. (C) 2003 Elsevier Ltd. All rights reserved.