Experimental verification of a predictive model of penetrant transport in glassy polymers

Abstract

The validity of the Lustig et al. ( Chem. Engng Sci. 47, 3037–3057, 1992) model for penetrant transport in glassy polymers was investigated by comparing experimental results of dodecane transport in crosslinked polystyrene samples with the model. All parameters of the model were measured independently. The time-dependent concentration profiles at the dodecane/polystyrene interface were predicted at various temperatures. The time-dependent concentration and the polymer stress profiles within the dodecane/polystyrene system indicate a wide range of transport mechanisms at different temperatures. The dodecane transport kinetics was affected by dodecane diffusion coefficient, the discrete viscoelastic relaxation time and the modulus of the dodecane/polystyrene system. The significance of the viscoelastic relaxation contribution on the overall penetrant transport was evaluated by analyzing the temperature dependence of the diffusional exponent, n, of a simple exponential dependence of the dodecane uptake as a function of transport time. The diffusional exponent and the resulting penetrant transport kinetics were correlated to the mean diffusion Deborah number. In general, the transport process was closely characterized as Fickian diffusion far above or far below the glass transition temperature of the system and as anomalous transport close to the glassy/rubbery transition