Effective χ in a lattice theory of mixtures

Using general thermodynamic arguments for an incompressible lattice system, we demonstrate that the effective {χ} must be a complicated function of temperature, composition, polymerization indices, and the coordination number of the lattice, even though the bare {χ} is merely a parameter. We go beyond the random mixing approximation and present a lattice theory of mixtures which yields an effective {χ} consistent with experiments. {} 1996 The American Physical Society.