Swelling of a model polymer network by a one-site solvent: Computer simulation and Flory-Huggins-like theory - art. no. 051801

A molecular-dynamics-Widom test particle-simulation was used to investigate the swelling of a model polymer network in contact with a one-site solvent under subcritical and supercritical conditions. Particle motion is compute d via molecular dynamics. Simultaneously, the solvent particle concentratio n is controlled by direct comparison of the chemical potentials in two refe rence systems (pure solvent and network including solvent), which are calcu lated using Widom's test particle method. The simulated swelling isotherms exhibit complex behavior: at the subcritical conditions considered here, th e swelling ratio decreases with increasing pressure. At the intermediate su percritical temperatures the isotherms exhibit a peak, which disappears wit h the elevation of temperature. At high temperatures, the swelling ratio of the network increases monotonically with increasing pressure. The correspo nding isobars also exhibit a maximum, which broadens and shifts to higher t emperatures with increasing supercritical pressure. These results are in qu alitative agreement with the prediction of a modified Flory-Huggins theory and with the results of known experiments. Furthermore, the selfdiffusion c oefficients of the solvent in the network and in its pure state are simulat ed. The solvent mobility in the network is significantly decreased because of the hindrance of network beads, but exhibits different behavior at subcr itical in comparison to supercritical temperatures.