Activation energy diffusion, sorption, permeation

Permeability is so low that, in sorption experiments, large pressure differences and membranes of small thickness have to be employed. These restraints do not apply to condensable vapours or highly permeant gas. In the last case, relaxation processes in the polymer matrix cause changes in the transport behaviour and make the permeability time-dependent. In contrast, only vapours of sufficiently high solubiUty are suitable for the gravimetric measurements used in the sorption experiments. Consequently, there are only few systems for which both sorption and permeation results have been reported. Low et al. conducted the two types of moisture transport experiments on a polyamide 6/elay nanocomposite. The authors found that the activation energy of moisture permeation obtained from the sorption experiment is lower than that derived from the permeation measurement. They concluded that the interaction and contribution of the diffusion and solubility parameters show complex transport behaviour in these nanocomposite films. 

The 75/25 NR/LLDPE blend exhibited the highest amount of Q, of toluene at the temperatures studied. The diffusion, permeation, and sorption coefficients were obtained for toluene in the various blends. The transport of toluene through the 60/40 NR/LLDPE blend was found to be Fickian at 55 °C, pseudo-Fickian at 35 °C, while for the other blends at the temperatures studied, it was anomalous. The calculated activation energies of diffusion and permeation in the rubber blends were all positive, and were found to decrease with an increase in the amount of NR in the blends. The calculated heat of sorptions for the blends were all positive. 

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