Group-contribution coarse-grained molecular simulations of polystyrene melts and polystyrene solutions in alkanes using the SAFT-γ force field

A coarse-grained (CG) model for atactic polystyrene is presented and studied via classical molecular dynamics simulations. The interactions between the CG segments are described by Mie potentials, with parameters obtained from a top-down approach using the SAFT-γ methodology. The model is developed by taking a CG model for linear-chain-like backbones with parameters corresponding to those of an alkane model, and decorating it with side branches with parameters taken from a model of toluene, which are thus “aromatic-like” in nature. The model is validated against the properties of monodisperse melts, including the effect of temperature and pressure on density, as well as structural properties: radii of gyration and end-to-end distances as functions of chain length. The model is employed within large-scale simulations that describe the temperature-composition phase behaviour of binary mixtures of polystyrene in n-hexane and n-heptane. A single temperature-independent energy cross-interaction parameter is estimated for each solvent to reproduce experimental solubility behaviour; this is sufficient for the quantitative prediction of both upper and lower solution critical points and the transition to the expected “hour-glass” phase behaviour.