Square-well chain mixture: analytic equation of state and Monte Carlo simulation data

An analytic perturbation theory equation of state developed for mixtures of freely-jointed square-well chain fluids of variable well width is tested against Monte Carlo simulation data. The equation of state is based on second-order Barker and Henderson perturbation theory to calculate the thermodynamic properties of the reference sphere fluid, and on first-order Wertheim thermodynamic perturbation theory to account for the connectivity of spheres to form chains. A real function expression for the radial distribution function of hard spheres and one-fluid type mixing rule are used to obtain an analytic, closed form expression, for the Helmholtz free energy of mixtures of square-well spheres. In order to test the theories, Monte Carlo simulations for binary mixtures of square-well chains were performed to obtain the radial distribution function at the contact point, the compressibility factor, and the configurational internal energy of these mixtures. The proposed equation of state leads to good predictions of compressibility factor of square-well chains and their mixtures when compared with the simulation data.