Title: self-diffusion coefficient
Long Title: IUPAC Gold Book - self-diffusion coefficient
DOI: 10.1351/goldbook.S05582
Status: current

Definition
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 \[D_{i}^{*}=D_{i}\ \frac{\partial (\ln c_{i})}{\partial \ln a_{i}}\] 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.

Related Terms
- chemical potential: https://goldbook.iupac.org//terms/view/C01032
- diffusion: https://goldbook.iupac.org//terms/view/D01716
- diffusion coefficient: https://goldbook.iupac.org//terms/view/D01719
- gradient: https://goldbook.iupac.org//terms/view/G02669
- isotope effect: https://goldbook.iupac.org//terms/view/I03327
- isotopically labelled: https://goldbook.iupac.org//terms/view/I03336
- tracer: https://goldbook.iupac.org//terms/view/T06422

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 (https://doi.org/10.1351/pac197231040577)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/S05582/html
- json: https://goldbook.iupac.org/terms/view/S05582/json
- xml: https://goldbook.iupac.org/terms/view/S05582/xml

Citation: Citation: 'self-diffusion coefficient' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.S05582
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Accessed: 2026-07-02T13:46:55+00:00