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.