{"term":{"id":"05582","title":"self-diffusion coefficient","longtitle":"IUPAC Gold Book - self-diffusion coefficient","doi":"10.1351\/goldbook.S05582","code":"S05582","status":"current","definitions":[{"id":1,"text":"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.","links":[{"term":"chemical potential","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C01032"},{"term":"diffusion","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/D01716"},{"term":"diffusion coefficient","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/D01719"},{"term":"gradient","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/G02669"},{"term":"isotope effect","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03327"},{"term":"isotopically labelled","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I03336"},{"term":"tracer","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/T06422"}],"sources":["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)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/S05582\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/S05582\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/S05582\/plain"},"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","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-07-02T13:46:15+00:00"}}