Thermodynamics of the polymer mean-spherical ideal chain approximation for a fluid of linear chain molecules

Abstract

A mean-spherical approximation (MSA)-like theory is proposed for the site-site molecular fluid represented by hard sphere totally flexible linear chain molecules with a long range site site pair potential of arbitrary type outside the hard core region. The theory is based on the complete association limit of the polymer mean-spherical approximation (PMSA) supplemented by the so-called ideal chain approximation, and belongs to the class of the site-site integral equation theories that are ‘proper’ in the sense of Chandler and coworkers. Both approximations have been used recently in the frame of the multidensity integral equation theory for associating fluids. In the simplest case of chain length 2 the present approach reduces to the Chandler-Silbey-Ladanyi (CSL) equation closed by the corresponding MSA closure conditions. The Hoye-Stell scheme of calculating thermodynamic properties is extended and expressions for the Helmholtz free energy, chemical potential and pressure are derived. The theory is illust...