Pressure-dependent permeation of noble gases (He, Ne, Ar, Kr, Xe) through thin membranes of oriented polypropylene (OPP) studied by mass spectrometry.

Abstract

A mass spectrometric method has been used to study transmission of noble gases (He, Ne, Ar, Kr, Xe) through thin polymer membranes of OPP and PET. The transmission of gas originating from a confined volume in a gas cell through the membrane is measured by a mass spectrometer. Due to depletion of gas inside the gas cell, transmission decreases as a function of time, which is taken as a measure for permeation. For the smaller noble gases helium and neon gas transmission is found to be an exponential function of time indicating a pressure independent permeability for PET and OPP. For the permeation of heavier noble gases xenon, krypton and — to a lesser extent — argon through OPP a pressure dependent permeability was found. A model takes into account the higher solubility for bigger gas atoms as they have a higher probability to condense in cavities of the free volume of the polymer. There is good agreement between experimental and calculated data. Sensitivity of the mass spectrometric method is discussed for argon isotopes 40Ar, 38Ar and 36Ar and shows an instrumental detection limit of less than 0.1%.