Sedimentation of C60 and C70: Testing the Limits of Stokes' Law.

Virtually all dynamic methods for determining particle size on the nanoscale use the Stokes-Einstein-Sutherland (SES) equation to convert the diffusion coefficient into a hydrodynamic radius. The validity of this equation on the nanoscale has not been rigorously validated by experiment. Here we measure the sedimentation rates and diffusion coefficients of C60 and C70 in toluene using analytical ultracentrifugation and compare the results to the SES equation. We find that the SES equation for the drag force (nonslip boundary condition) works down to 1 nm length scales.