SORPTION AND DIFFUSION OF VOLATILE ORGANIC-COMPOUNDS IN POLYDIMETHYLSILOXANE MEMBRANES

Sorption and diffusion of ethanol, 1,1,1-trichloroethane (TCA), and tr ichloroethylene( TCE) were investigated in polydimethylsiloxane (PDMS) membranes using a gravimetric technique. The thermodynamic equilibriu m and kinetic properties were evaluated at temperatures of 25, 100, an d 150 degrees C. The sorption isotherms for TCA and TCE can be correla ted well using the Flory-Huggins model. However, a three parameter Kon ingsveld-Kleinjtens variation to the Flory-Huggins equation is require d for correlation of the ethanol isotherm. The solubility coefficients of TCA and TCE increase with activity, but it remains almost constant for ethanol. The calculated sorption energies reveal high positive he at of mixing for ethanol. TCA and TCE sorption in PDMS decreases stron gly with temperature as opposed to ethanol. Clustering function analys is is used to explain the anomalous ethanol sorption and diffusion beh avior in PDMS. TCA and TCE diffusivities do not exhibit large variatio ns with volatile organic compound activity. However, ethanol demonstra tes a maxima in its diffusivity at activities where it has minimum clu stering tendencies. (C) 1998 John Wiley & Sons, Inc.