A theory for the thermodynamics and structure of nonuniform systems, with applications to the liquid–vapor interface and spinodal decomposition

We propose a theory for the description of the thermodynamics and structure of nonuniform fluids. The theory is based on a generalization of liquid-state perturbation theory of uniform fluids and on the Fisk–Widom generalization of the thermodynamic theory of van der Waals and Cahn–Hilliard. The theory is applied to the liquid–vapor interface near the triple point and near the critical point, and to the thermodynamic analysis of the stability of a single phase fluid in the spinodal region (spinodal decomposition). The limitations of the van der Waals/Cahn–Hilliard theory for surfaces and Cahn’s analysis for spinodal decomposition are discussed.