https://doi.org/10.1351/goldbook.MT07230

Capability of a mixture to form a single phase over certain ranges of temperature, pressure, and composition.**Notes: **

*Source: *

PAC, 2004,*76*, 1985. 'Definition of terms related to polymer blends, composites, and multiphase polymeric materials (IUPAC Recommendations 2004)' on page 1987 (https://doi.org/10.1351/pac200476111985)

- Whether or not a single phase exists depends on the chemical structure, molar-mass distribution, and molecular architecture of the components present.
- The single phase in a mixture may be confirmed by @L03525@, X‑ray @S05487@, and @N04116@ @S05487@.
- For a two-component mixture, a necessary and sufficient condition for @S05900@ or @M03872@ equilibrium of a homogeneous single phase is \[\left ( \frac{\delta^{2}\Delta _{\text{mix}}G} {\delta\phi ^{2}} \right)_{T,p} > 0,\] where Δ mix G is the Gibbs energy of mixing and ϕ the composition, where ϕ is usually taken as the @V06643@ of one of the components. The system is @U06569@ if the above second derivative is negative. The borderline (@ST07274@) between @M03872@ and @U06569@ states is defined by the above second derivative equalling zero. If the compositions of two conjugate (coexisting) phases become identical upon a change of temperature or pressure, the third derivative also equals zero (defining a critical state).
- If a mixture is thermodynamically @M03872@, it will demix if suitably nucleated. If a mixture is thermodynamically @U06569@, it will demix by @S05869@ or by @N04244@ if suitably nucleated, provided there is minimal kinetic hindrance.

PAC, 2004,