TRANSLATIONAL DIFFUSION IN C60 AND C70 FULLERENE SOLUTIONS

Self-diffusion coefficients D of C60 and C70 and of the solvent molecu les C6H6 and CS2 have been investigated in liquid fullerene solutions by the C-13 and H-1 NMR pulsed field gradient techniques. The C60/benz ene measurement is in good agreement with a recent report, while data obtained for C60/CS2 and C70/CS2 are first measurements. The C70 numbe r reflects the only diffusion measurement yet carried out on this mole cule. Data were obtained with 5% C-13 enriched fullerenes at 298 K. Th e sample preparation and the separation of C-13 enriched C60 and C70 i s described. The fullerene diffusion data are in excellent agreement w ith values predicted by the Stokes-Einstein equation, however, under s lip boundary conditions. In CS2 solution we find D (C60) = (1.85 +/- 0 .18) x 10(-9) m2 s-1 and D(C70) = (1.56 +/- 0.16) x 10(-9) m2 s-1 at 2 98 K, thus showing that fullerenes differing slightly in shape can be discriminated via their diffusivity. C70 may be regarded as an ideal e llipsoidal particle for the test of theories of diffusion. Our experim ental result for C70 indicates that the long semi-axis of the ellipsoi d determines the diffusion behavior. Preliminary temperature dependent diffusion measurements of C60 in CS2 do not reveal a difference in th e activation energy of solute and solvent. We could not detect that th e diffusion coefficients of the solvent molecules are influenced by th e presence of the fullerenes in the solutions under investigation.