Swelling of a model network: A Gibbs-ensemble molecular dynamics study

We perform molecular simulations to study the swelling of a model network i n contact with different chain-like solvents. The method is Gibbs-ensemble molecular dynamics, which is a molecular dynamics implementation of the con cept underlying the Gibbs-ensemble Monte Carlo method. We simulate swelling isotherms for three coarse-grained solvents with one (S-1), six (S-6), and twelve (S-12) centers in the high pressure regime at supercritical tempera tures. The simulated swelling isotherms of the S-1-solvent exhibit a maximu m near the critical pressure which decreases and shifts towards higher pres sures with increasing temperature. Based on a modified Flory-Huggins approa ch, a set of numerically soluble equations is derived in order to reproduce the simulated isotherms. The resulting theoretical isotherms are in very g ood qualitative agreement with the simulations. Comparison of the different solvents shows also that the swelling ratio decreases when the chain lengt h of the solvent increases. (C) 2000 American Institute of Physics. [S0021- 9606(00)50111-1].