Capability of a mixture to form a single phase over certain ranges of temperature, pressure, and composition.
  1. Whether or not a single phase exists depends on the chemical structure, molar-mass distribution, and molecular architecture of the components present.
  2. The single phase in a mixture may be confirmed by @L03525@, X‑ray @S05487@, and @N04116@ @S05487@.
  3. 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).
  4. 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, 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)