= Spinodal decomposition
<Spinodal decomposition> is spontaneous growth of composition fluctuations in a homogeneous mixture whose local mixing <free energy> has negative composition curvature. For a mean $\phi$, equal regions at $\phi\pm\delta\phi$ change the mean free energy by $f''(\phi)(\delta\phi)^2/2+O((\delta\phi)^4)$, which is negative inside the <spinodal>. Interfacial costs suppress sufficiently short wavelengths, while conservation of composition constrains the dynamics. Outside the spinodal but inside the <binodal>, the uniform state is instead <metastable> and requires <nucleation> to begin separation.
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