self-diffusion coefficient

The diffusion coefficient $D i *$ of species $i$ in the absence of a chemical potential gradient. It is related to the diffusion coefficient $D i$ by

$D i * = D i ∂ ( ln c i ) ∂ ln a i$

where $a i$ is the activity of $i$ in the solution, and $c i$ is the concentration of $i$ . If an isotopically labelled species ( $i *$ ) is used to study diffusion, the tracer diffusion coefficient, $D i *$ , is practically identical to the self-diffusion coefficient provided that the isotope effect is sufficiently small.

Source:

PAC, 1972, 31, 577 (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 617