LATTICE THERMODYNAMICS FOR BINARY CLOSED-LOOP EQUILIBRIA - ORDINARY AND POLYMER SYSTEMS

The incompressible lattice-gas model by ten Brinke and Karasz is adopt ed to introduce the effect of specific interactions into a recently-pr esented Monte-Carlo-based lattice expression for the Helmholtz energy of nonrandom mixing. While the lattice remains incompressible, intermo lecular forces consist of two types: London dispersion forces and spec ific (chemical) forces. The specific interactions between similar comp onents, as well as those between dissimilar components, are incorporat ed in a systematic manner. Closed-loop temperature-composition phase d iagrams are obtained. The theory is compared with experimental data fo r several binary systems, including polymer solutions, which exhibit c losed-loop coexistence curves. Theoretical and experimental results ar e in good agreement.