Term: spinodal
https://doi.org/10.1351/goldbook.ST07274

Definition:
Curve defining the region of composition and temperature for a binary mixture across which a transition occurs from conditions where single-phase mixtures are metastable to conditions where single-phase mixtures are unstable and undergo phase separation by spinodal decomposition.

Notes:
0) The spinodal curve for a binary mixture is defined as the geometrical locus of all states with \[\left ( \frac{\delta^{2}\Delta _{\text{mix}}G}{\delta\phi ^{2}} \right)_{T,p} = 0\].
1) In the @U06569@ region bounded by the spinodal curve, @PT07286@ separation is spontaneous, i.e., no nucleation step is required to initiate the separation process.

Related Terms:
1) unstable (http://doi.org/10.1351/goldbook.U06569).
2) phase domain (http://doi.org/10.1351/goldbook.PT07286).
3) metastable (http://doi.org/10.1351/goldbook.M03872).
4) phase separation (http://doi.org/10.1351/goldbook.P04534).
5) spinodal decomposition (http://doi.org/10.1351/goldbook.S05869).

Source: PAC, 2004, 76, 1985. 'Definition of terms related to polymer blends, composites, and multiphase polymeric materials (IUPAC Recommendations 2004)' on page 1998 (https://doi.org/10.1351/pac200476111985)

Citation: 'spinodal' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.ST07274

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.

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.