Self-consistent integral equation theory for the equilibrium properties of polymer solutions

Abstract

Self-consistent RISM integral equation theory of polymeric liquids is used to investigate the equilibrium properties of polymer solutions and melts. Density functional formalism is employed to derive the effective medium-induced potential between two sites on a polymer chain. The resulting expression leads to a coupling between the interchain and intrachain pair correlation functions. An approximate method for the calculation of the effective intrachain pair correlations is examined. The method employs Monte Carlo computer simulations of a single polymer chain interacting via local chemical interactions, long-range excluded volume, and the self-consistently determined medium-induced potential in the condensed phase to compute the intrachain pair correlations which are consistent with the interchain packing. Results for solutions of tangent hard-sphere chains are compared to recent off-lattice Monte Carlo simulations for various chain lengths and densities. In particular, it was found that the theory slightly overestimates the average size of the polymers in solution, while the density dependence of the average size of the chains is in good agreement with the Monte Carlo simulations. The inclusion of the self-consistent determination of the intrachain correlations is found to significantly alter the interchain pair correlation function at low and intermediate densities.