Thermodynamic properties of hard-chain molecules

The density and molecular size dependence of the equation of state for molecules that consist of freely jointed, tangent hard spheres is investigated. It is shown that the properties of hard-chain molecules can be accurately described using the properties of spherical molecules and a function c which varies approximately linearly with the reduced density. Monte Carlo and molecular dynamics simulation data for hard chains were used to develop the expression for c. The new equation of state is simple in form and more accurate for the calculation of compressibility factors for hard-chain molecules than either Wertheim's first-order thermodynamic perturbation theory or the generalized Flory dimer theory (GFD). Further, this new equation reduces to the correct second virial coefficient limit as the density approaches zero