MOLECULAR THERMODYNAMICS APPROACH FOR BINARY POLYMER-SOLUTIONS ON THENONRANDOM MIXING EFFECT

The lattice model gives a starting point for a theoretical description of the thermodynamic properties of polymer solution systems. Classica l models, such as the Flory-Huggins model and the quasi-chemical model , present too narrow or parabolic coexistence curves when compared wit h experimental data. It is well known that failures of the lattice mod el are due to mathematical approximations for the effects of nonrandom mixing in order to gain an analytical solution. Moreover, the existin g configurational energy of mixing, in which the residual terms are tr uncated, results in significant errors in the prediction of the coexis tence curve calculations for polymer solution systems. The proposed mo del in this study improves the mathematical approximation defect and g ives a new expression for the configurational energy of mixing. To cor relate the energy of mixing term, including the effect of non-random m ixing on the configurational thermodynamic properties of a binary mixt ure with simulation data, we use Monte-Carlo simulation data. Monte-Ca rlo simulation gives essentially exact results for the lattice model. The configurational Helmholtz energy is obtained upon combining the Gi bbs-Helmholtz equation with Guggenheim's athermal entropy of mixing as a boundary condition. The coexistence curves generated by the propose d model are compared with experimental data. (C) 1997 Elsevier Science Ltd.