Application of vapour phase calibration method for determination of sorption of gases and VOC in polydimethylsiloxane membranes

Abstract

Equilibrium sorption of oxygen, carbon dioxide, ethylene, dimethyl sulphide, trichloroethylene and toluene in polydimethylsiloxane (PDMS) at 30 °C is reported. Sorption isotherms of all compounds are well described by Henry’s law within the concentration intervals studied (0.008–257 g m −3). Vapour phase calibration (VPC), a static headspace method, was applied instead of the usual gravimetric and barometric sorption methods. Simple, rapid and reliable determination of air-PDMS partition coefficients ( S) varying between 1 and 900 (g m −3/g m −3) was achieved by this method. Solubility of toluene in PDMS was the best of all tested compounds, followed by trichloroethylene, dimethyl sulphide, ethylene, carbon dioxide and oxygen. This observed sequence can be explained by the penetrant condensability, expressed by its critical temperature ( T c). Only for ethylene, a higher solubility is measured than expected from the correlation between S and T c. This is caused by the relative high interaction of ethylene with the polymer. The Flory–Rehner interaction parameter, χ, for ethylene was calculated 0.004 while the χ values of the other compounds varied between 0.37 and 0.80. The solubility coefficients are shown to be independent on relative air humidity. For the compounds and concentration levels studied, the sorption of dimethyl sulphide is unaffected by the simultaneous sorption of other VOC. This non-competitive behaviour is consistent with the linear partition mechanism.