Equation of state for thermodynamic properties of chain fluids near-to andfar-from the vapor-liquid critical region

Upon incorporation of contributions from long-wavelength density fluctuatio ns by a renormalization-group theory, a crossover equation of state is deve loped for describing thermodynamic properties of chain fluids. Outside the critical region, the crossover equation of state reduces to the classical e quation; inside the critical region, it gives nonclassical universal critic al exponents. The crossover equation of state correctly represents phase eq uilibria and pVT properties of chain fluids in both regions. Good agreement is obtained upon comparisons with computer simulations for square-well cha in fluids. As obtained from experimental vapor-pressure and density data, t he square-well segment-segment parameters for n-alkanes from ethane to eico sane are linear functions of molecular weight. Calculated thermodynamic pro perties agree well with experiment for n-alkanes from methane to hexatriaco ntane. (C) 1999 American Institute of Physics. [S0021- 9606(99)50337-1].