Equation of state for systems containing chainlike molecules

An equation of state for systems containing chainlike molecules is developed. The equation consists of three contributions. First, as a reference, we adopt the equation for hard-sphere-chain fluids (HSCF) derived through the r-particle cavity-correlation function of sticky hard spheres. The HSCF equation has a simple form similar to the Carnahan-Starllng equation and has been satisfactorily tested by computer-simulation results for chain fluids covering a wide range of chain length. A new mixing rule is derived when the HSCF equation is used for mixtures. Second, as a perturbation, we use directly the square-well potential (SW), Finally, for molecules with specific oriented interactions such as hydrogen bonding, we introduce contribution from chemical association (ASS) that comes naturally from the sticky model used in deriving the reference equation. The equation of state is widely tested by fitting experimental vapor pressures and pVT relations for pure substances, as well as vapor-liquid equilibria, excess enthalpy, and liquid-liquid equilibria for fluid mixtures containing ordinary molecules and chainlike macromolecules.