A 2-FLUID THEORY FOR CHAIN FLUID MIXTURES FROM THERMODYNAMIC PERTURBATION-THEORY

A two reference fluid equation of state is derived for mixtures consis ting of chain molecules, using Wertheim's first-order thermodynamic pe rturbation theory (TPT1). This equation of state is based on the compr essibility factors of two reference fluids of different chain lengths, and avoids the need to estimate the correlation functions of referenc e fluids. It is shown that the recently proposed pure fluid equation o f state based on observations of Wertheim's first-order perturbation t heory and generalized Flory theory due to Escobedo, F. A., and de Pabl o, J. J. (1995, J. chem. Phys., 103, 1946) and Sheng, Y.-J., Panagioto poulos, A. Z., and Kumar, S. K. (1995, J. chem. Phys., 103, 10 315) is a direct prediction of this approach. The present study involves a ri gorous 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 eq uations of state are recovered. The equation of state is shown to be i n good agreement with recent molecular simulation results for pure hom onuclear and alternating copolymer hard chain fluids.