Characterization of film transport properties for organic vapors using the time-lag method — interest and limitations

Abstract

The time-lag method can be easily used to characterize transport polymer features for permanent gases whereas with volatile organic vapors (VOCs) this routine procedure does not give valuable results, in particular in case of diffusion varying with activity, swelling of the polymer or small time-lag values. Working with VOCs under time-lag conditions, an imperfect pressure step arising at the upstream side of film was evidenced to be the source of a systematic error linked mainly to the kinetic of solvent vaporization. Thus the classical time lag cannot be straightly used to determine the diffusion coefficient. A simple modification intended to take into account the phenomena is proposed to overcome this problem and to enable a more accurate determination of the basic polymer features even with VOCs. Moreover, in order to validate this modification, a computable model was implemented. This model, combining a non-perfect step and transport through polymer, was computed with adequate values of parameters for comparison with experimental values.