Relation between mobility and size of nanodrops

The relation between mobility Z, charge z and mass diameter d = (6m/πρ)^1/3 of the cluster can be directly inferred from DMA-MS spectra of nanodrops, where all three variables are precisely known (m is the cluster mass, and ρ the bulk density of the cluster material). The figure on the left shows such a relation for nanodrops of the ionic liquid EMI-BF₄ in air. From these data one sees that the usual Stokes Millikan equation (continuous line) agrees almost exactly with the data down to 1.5 nm mass diameter. The figure also show that these nanodrops have the bulk density of EMI-BF₄, that ion dipole effects (polarization) are negligible, and that collisions are inelastic with accommodation coefficient α= 0.91.