Translational diffusion in C₆₀ and C₇₀ fullerene solutions

Abstract

Abstract Self‐diffusion coefficients D of C 60 and C 70 and of the solvent molecules C 6 H 6 and CS 2 have been investigated in liquid fullerene solutions by the 13 C and 1 H NMR pulsed field gradient techniques. The C 60 /benzene measurement is in good agreement with a recent report, while data obtained for C 60 /CS 2 and C 70 /CS 2 are first measurements. The C 70 number reflects the only diffusion measurement yet carried out on this molecule. Data were obtained with 5% 13 C enriched fullerenes at 298 K. The sample preparation and the separation of 13 C enriched C 60 and C 70 is described. The fullerene diffusion data are in excellent agreement with values predicted by the Stokes‐Einstein equation, however, under slip boundary conditions. In CS 2 solution we find D (C 60 ) = (1.85±0.18) × 10 −9 m 2 s −1 and D (C 70 ) = (1.56±0.16) × 10 −9 m 2 s −1 at 298 K, thus showing that fullerenes differing slightly in shape can be discriminated via their diffusivity. C 70 may be regarded as an ideal ellipsoidal particle for the test of theories of diffusion. Our experimental result for C 70 indicates that the long semi‐axis of the ellipsoid determines the diffusion behavior. Preliminary temperature dependent diffusion measurements of C 60 in CS 2 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.