Molecular and condition parameters dependent diffusion coefficient of water in poly(vinyl alcohol): a molecular dynamics simulation study

Diffusion behavior of water molecules in poly(vinyl alcohol) (PVA) was investigated by molecular dynamics (MD) simulation, and the diffusion coefficient of water molecules in PVA was calculated based on the Einstein's relation. The effects of polymerization degree, temperature, density, and pressure on the diffusion coefficient were conducted to gain insights into their diffusion mechanisms under different processing conditions. The results showed that the simulation data of diffusion coefficient was consistent with experimental values. With the increase of polymerization degree of PVA, the diffusion coefficient began with a sharp decrease and then became stable, while the diffusion coefficient increased with increasing temperature. It was also found that PVA matrix with a smaller cell density had a larger free volume, and then, the diffusion coefficient was larger. The H2O sorption isotherm could be described by the Langmuir sorption isotherm, and the diffusion coefficient decreased with the increase of pressure.