Vapour sorption and permeation properties of poly ( dimethylsiloxane ) films *

Sorption and permeation of several organic vapours in poly(dimethylsiloxane) were investigated. Solubility and permeability coefficients measured show a strong dependence of the applied vapour activity typical for these systems, contrary to the behaviour of permanent gases. However, as irregularities in the series of chloromethanes show, highest sorption does not necessarily lead to the highest permeability value. A possible explanation of this effect can be found in the concentration dependent diffusion behaviour of poly(dimethylsiloxane) toward these organic vapours. Thus, from the kinetics of solvent uptake, i.e. the sorption isotherms over time, the diffusion coefficients, which were corrected for swelling and thermodynamic activity of the vapour, were calculated for the different vapour activities.