Monday, November 8, 2010: 2:18 PM
250 A Room (Salt Palace Convention Center)
Polymer chains confined in nanopores are in a delicate balance. Confined chains have an enthalpic advantage from the adsorption forces, yet suffer an entropic penalty relative to the same chain in a dilute solution. Knowledge of these energetics yields information on partitioning and thus helps describe the mechanics of systems such as polymer chromatography. Our work aims to describe this interplay from an atomistic simulation viewpoint. The adsorption characteristics of long, flexible, chains of harmonically bonded Lennard-Jones monomers was studied using incremental gauge cell Monte Carlo. The incremental gauge cell method allows for calculation of the chemical potential of the difference between chains of N and N + 1 monomers, and thus the chemical potential of the chain and its free energy. Chains were simulated in the zero-density limit and in spherical confinements. Confined chains were also simulated with varying adsorption potentials. Free energy scaling results are compared to theoretical predictions. We found that chains adsorbing at high temperatures suffer a large energetic penalty, while low temperature chains are found to adsorb in layers and exhibit a phase transition from layering to ‘filled' pore state, superficially similar to physisorption of fluids.