Molecular thermodynamics of binary polymer solutions using modified doublelattice model: Chain length dependence of primary lattice

In a previous study we modified a double lattice model by introducing a new interaction parameter, which improved the mathematical approximation defec t, and gave a new expression for the Helmholtz energy of mixing. In the mod el the universal constants C-beta and C-gamma in the primary lattice were d etermined by comparing them with literature Monte Carlo simulation data, wh ich is the only case for r(1) = 1 and r(2) = 100 (case I). In this study we introduce new universal constants, C-beta and C-gamma, as a function of th e chain length of a polymer in a solvent (case II) by comparing them with o ther literature simulation data for various polymer chain lengths. The prop osed model is compared with polymer-solvent systems. In an upper critical s olution temperature phase behavior the theoretical results of case II were improved over those of case I. However, in a lower critical solution temper ature phase behavior those of case I were not very sensitive to C-beta and C-gamma. (C) 1999 John Wiley & Sons, Inc.