Some universality in subcritical behavior of real substances and model fluids

On the basis of the latest advances in Mayer's cluster-based approach, the reduced forms of the well-known virial expansions are derived in terms of scaled reducible and irreducible cluster integrals. This transformation minimizes the dependence on temperature and the effect of parameters specific for each thermodynamic system, thus making the resulting reduced expansions indeed universal on the quantitative level. In particular, the scaling of isotherms and saturation curves for various systems (the Lennard-Jones model, different lattice gases, and real substances with simple nonpolar molecules as well as complex polar ones) confirms the approximate universality of the proposed reduced variables for temperature, pressure, and density at subcritical gaseous states up to the saturation point. In addition, the temperature dependence of the correspondingly scaled second virial coefficients also appears similar for various systems.