Lattice theory of solvation in macromolecular fluids. III. Monte Carlo simulations

Abstract

Monte Carlo simulations are used to calculate the energy, free energy, and entropy of solvation in a lattice model of polymer host. The solute particle interacts with specific beads in the host chain at nearest neighbor sites. The results are used to check the accuracy of the quasichemical approximation (QCA) recently used [Olender and Nitzan, J. Chem. Phys. 101, 2338 (1994)] to study ion solvation and ion pair dissociation in polymer hosts. For noninteracting chains we find that the QCA is very accurate when the solvent consists of homogeneous chains (all beads interact equally with the impurity), and give errors of up to 20% when nonhomogeneous chains (with some of the beads interacting with the impurity) are used. For interacting chains this trend is reversed and the QCA works better for nonhomogeneous chains. Deviations of the QCA prediction from the ‘‘exact’’ numerical results are traced to three-body and higher order correlations. The success of the QCA for interacting solvents of nonhomogeneous chains is associated with cancellation of opposing effects of such correlations.