The relation between osmotic flow and tracer solvent diffusion for single-file transport.

It is demonstrated that a reasonably general model for single-file passage of solvent through an ultra-narrow pore implies the equality of tracer diffusion and osmotic flow. This result is not trival, but follows from the exactly compensating effects of solvent-solvent interaction on the paritioning of bulk solvent into the pore and on the diffusion rate within the pore. A previous calculation of Longuet-Higgins and Austin is seen to be valid only in the absence of interactions among solvent molecules in the pore.