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Permeation of polymers — a computational approach

This article reviews the progress that has been made in recent years in computer modelling of the transport of small atoms, molecules and ions through synthetic polymers. We discuss the physical concepts behind phenomena such as sorption, diffusion, permeation and ionic conductivity and the techniques to study them by computer simulation: molecular dynamics and Monte Carlo simulation with atomistically detailed force fields as well as coarse-grained lattice models. Important results have been obtained at both the qualitative and quantitative level. The mechanisms underlying the diffusion of gas molecules and the mobility of ions could be observed in simulations and are now unambiguously established. Short-time irregularities in the motion such as anomalous diffusion have been found. Some quantities can be calculated very accurately (e.g.gas diffusion coefficients for low-barrier polymers), where for others only trends and relative orderings can be estimated (e.g.gas solubilities, ionic conductivities) at a semiquantitative level. Where possible, the range of applicability of various methods is indicated. Coarse-grain approaches are presented which extend the results obtained by atomistic models to longer length scales and thereby allow the treatment of heterogeneous materials such as semicrystal-line or filled polymers. We believe that computer simulation has enough to offer to make it a useful tool when studying or designing polymer membranes.