Molecular dynamics simulation of the diffusion coefficients of anthraquinone in poly(methyl methacrylate) swollen by supercritical carbon dioxide

The self-diffusion coefficients of anthraquinone in poly(methyl methacrylate) (PMMA) saturated with carbon dioxide were calculated by molecular dynamics simulations at 328.2 K and pressures of 13.1-20.2 MPa. The TraPPE potential model was adopted for anthraquinone and PMMA, and a single-site model was used for CO₂. Ten initial configurations were prepared under similar calculation conditions using the NTP ensemble to examine the dependence of the diffusion coefficient of anthraquinone on the initial configuration. The diffusion trajectories of anthraquinone were subsequently calculated using the NTV ensemble. The jumping motion of anthraquinone was found to depend on the initial configuration, and was noted to be related to the amount of CO₂ around anthraquinone, based on the analysis of the distribution functions of CO₂ and PMMA around anthraquinone. The diffusion coefficients of anthraquinone were calculated by averaging the mean square displacements obtained using the ten initial configurations. The calculated self-diffusion coefficients of anthraquinone were in good agreement with the experimental data.