Translational diffusion in C60 and C70 fullerene solutions

Abstract

Self-diffusion coefficients D of C60 and C70 and of the solvent molecules C6H6 and CS2 have been investigated in liquid fullerene solutions by the 13C and 1H NMR pulsed field gradient techniques. The C60/benzene measurement is in good agreement with a recent report, while data obtained for C60/CS2 and C70/CS2 are first measurements. The C70 number reflects the only diffusion measurement yet carried out on this molecule. Data were obtained with 5% 13C enriched fullerenes at 298 K. The sample preparation and the separation of 13C enriched C60 and C70 is described. The fullerene diffusion data are in excellent agreement with values predicted by the Stokes-Einstein equation, however, under slip boundary conditions. In CS2 solution we find D(C60) = (1.85±0.18) × 10−9 m2s−1 and D(C70) = (1.56±0.16) × 10−9m2s−1 at 298 K, thus showing that fullerenes differing slightly in shape can be discriminated via their diffusivity. C70 may be regarded as an ideal ellipsoidal particle for the test of theories of diffusion. Our experimental result for C70 indicates that the long semi-axis of the ellipsoid determines the diffusion behavior. Preliminary temperature dependent diffusion measurements of C60 in CS2 do not reveal a difference in the activation energy of solute and solvent. We could not detect that the diffusion coefficients of the solvent molecules are influenced by the presence of the fullerenes in the solutions under investigation.