Molecular dynamics model of absorption of water in polymers

We report a molecular dynamics simulation of the absorption of water in polymers. We embed a relatively large repeat unit containing several characteristic chemical groups in a molecular dynamics model of water which includes the internal dynamics of the water molecule. Potentials describing the interaction of the water with the repeat unit were taken from the work of Jorgensen and co-workers. We calculated the density of water around oxygen in ester, ether and alcohol groups in the repeat unit. We find in this model that the water is only bound by the alcohol group in agreement with recent experimental results. We have computed the infrared absorption spectrum of the bound and unbound water in this model. We find shifts which should be observable in the position of the stretch and librational frequencies due to binding of the water. We discuss implications for the dual diffusion model of water in polymers.