A two-fluid theory for chain fluid mixtures from thermodynamic perturbation theory

Abstract

A two reference fluid equation of state is derived for mixtures consisting of chain molecules, using Wertheim's first-order thermodynamic perturbation theory (TPT1). This equation of state is based on the compressibility factors of two reference fluids of different chain lengths, and avoids the need to estimate the correlation functions of reference fluids. It is shown that the recently proposed pure fluid equation of state based on observations of Wertheim's firstorder perturbation theory and generalized Flory theory due to Escobedo, F. A., and de Pablo, J. J. (1995, J. chem. Phys., 103, 1946) and Sheng, Y.-J., Panagiotopoulos, A. Z., and Kumar, S. K. (1995, J. chem. Phys., 103, 10315) is a direct prediction of this approach. The present study involves a rigorous derivation of the equation of state, and provides the basis to extend the equation of state to mixtures. For particular chain lengths of the two reference fluids, the equivalence of the SAFT and SAFTD equations of state are recovered. The equation of state is shown to be in good agreement with recent molecular simulation results for pure homonuclear and alternating copolymer hard chain fluids.