We prove the existence of a first-order, entropy-driven demixing transition in a simple lattice model for a hard-core mixture. The existence of this transition follows from the fact that this lattice model can be mapped onto an Ising model with nearest-neighbor interactions for which the phase behavior is known. The same mapping leads to a very simple interpretation of the entropic contribution of the solvent to the interaction parameter χ in the Flory-Huggins theory of polymer solutions.

• Received 27 February 1992

DOI:https://doi.org/10.1103/PhysRevLett.68.3363