Modelling of solid polymers in chemical detail ‐ gases in amorphous polymers

Abstract

AbstractThe diffusion of gases in dense polymers, above and below the glass‐transition temperature, is described with a new Transition State Theory model that is based on the concept that the dynamics of small molecules dissolved in dense polymers is separated from the structural relaxation of the dense polymers. The model is used to study the dynamics of rare gases dissolved in atomistic micro‐structures of four polymers at 300 K: poly(dimethylsiloxane), poly(isobutylene), atactic poly(vinylchloride) and the polycarbonate of 4,4′‐isopropylidenediphenol (bisphenol‐A). Short‐time‐scale MD runs (5 ps) are used to characterize the elastic thermal motion of the host matrix; this information on mobility is then used for a stochastic simulation of solute dynamics up to ca. 1ms. All dissolved molecules show similar behavior by displaying three time regimes: a short‐time, high‐mobility domain, an intermediate time domain of anomalous diffusion, and a diffusive regime at long times. From the long‐time data diffusion coefficients are estimated; comparison with experimental data results in good agreement.