Square-well chain molecules: a semi-empirical equation of state and Monte Carlo simulation data

A semi-empirical equation of state was developed for square-well chain fluids on the basis of Monte Carlo (MC) simulation data. The equation was formed by combining terms describing non-bonded square-well segments, hard-sphere chain formation, and a perturbation term describing the square-well contribution to chain formation. The functional dependence on the chain length is the same as that derived in the statistical associating fluid theory (SAFT). Extensive isobaric–isothermal MC simulations were performed for the dimer, 4-mer, 8-mer, and 16-mer square-well fluids at temperatures below or near the critical point. The new equation satisfactorily represents the volumetric properties of square-well chain fluids, up to and including the 100-mer, which was the longest chain length studied. Additionally, the new model accurately reproduces the phase envelopes of the dimer and 4-mer fluids, however, it underestimates the vapor pressures for 8-mer’s and above.