Title: micro-emulsion
Long Title: IUPAC Gold Book - micro-emulsion
DOI: 10.1351/goldbook.14317
Status: current

Definition
Dispersion made of water, oil, and surfactant(s) that is an isotropic and thermodynamically stable system with dispersed domain diameter varying approximately from \(\pu{1 nm}\) to \(\pu{100 nm}\), usually \(\pu{10 nm}\) to \(\pu{50 nm}\).

Notes
1) In a micro-emulsion the domains of the dispersed phase are either globular or interconnected (to give a bicontinuous micro-emulsion).
2) The average diameter of droplets in macro-emulsion (usually referred to as an "emulsion") is close to one millimeter (i.e., \(\pu{E-3 m}\)). Therefore, since micro- means \(\pu{E-6 m}\) and emulsion implies that droplets of the dispersed phase have diameters close to \(\pu{E-3 m}\), the micro-emulsion denotes a system with the size range of the dispersed phase in the \(\pu{E-6} \times \pu{E-3 m} = \pu{E-9 m}\) range.
3) The term "micro-emulsion" has come to take on special meaning. Entities of the dispersed phase are usually stabilized by surfactant and/or surfactant-cosurfactant (e.g., aliphatic alcohol) systems.
4) The term "oil" refers to any water-insoluble liquid.

Related Term
- dispersed phase: https://goldbook.iupac.org//terms/view/14307

Source
- PAC, 2011, 83, 2229. 'Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)' on page 2239 (https://doi.org/10.1351/PAC-REC-10-06-03)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/14317/html
- json: https://goldbook.iupac.org/terms/view/14317/json
- xml: https://goldbook.iupac.org/terms/view/14317/xml

Citation: Citation: 'micro-emulsion' 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.14317
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: 2026-07-14T19:54:02+00:00