Equation of state for the square-well chain fluid based on the dimer version of Wertheim's perturbation theory

Abstract

An equation of state for the freely jointed square-well chain fluid developed using Wertheim's thermodynamic perturbation theory and incorporating structural information on the square-well dimer fluid (TPT-D) is tested against the results of the Monte Carlo (MC) simulations. The performance of Wertheim's first order thermodynamic perturbation theory (TPT1) and the TPT-D theory are evaluated using MC simulation results for the square-well monomers and square-well dimers to avoid introducing errors due to approximations in evaluating the thermodynamic properties of the reference fluids. The dimer version of Wertheim's thermodynamic perturbation theory (TPT-D) increases the accuracy of the predicted value of compressibility factor of chain fluids in all ranges of density and temperature studied. To obtain the thermodynamic properties needed, NVT MC simulations were performed for the bulk phase of the square-well monomer, and for dimer, 4-mer, 8-mer and 16-mer square-well chain fluids. These MC simulation results are very accurate, and make possible a careful comparison between the TPT1 and TPT-D equations of state.