Gas Permeability Measurements Of Membranes Using The Difference Method

The investigation of gas permeation through different membranes is of great interest. Several issues existed in commercial testing, such as the influence of the background pressure, the uniformity of measured gas, and so on.This paper presents a new permeation measurement facility based on the difference method, which is shown to be capable of measuring gas fluxes through different polymeric membranes. The experiments have demonstrated that the residual pressure difference between two chambers is lower than 0.1Pa and the tolerance caused by outgassing can be neglected due to the introduction of the reference chamber, which helped to decrease deviation in the measurement of permeation.This paper aims to propose a new gas permeability test facility based on the difference method, transmission cell, hardware and software system of data acquisition. The permeation flux was examined by measuring the pressure difference between the reference and measurement chambers. Pure nitrogen, helium, oxygen permeation was performed through polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET) membranes using this method. The gas permeability of the same penetrant decreased in the following order based on the membrane material type comparison:kPMDS>kPI>kPET The gas permeability of the same membranes decrease in the following order:kO2> kN2> kHe.Thus, the gas permeability in the membrane decreases with increasing glassy transition temperature and increases with increasing critical temperature. The results from the experiments are even more convincing compared with the data obtained with the leak detector. Finally, the key parameter (the volume of the reference chamber and the measurement chamber) was measured using the static expansion method. The uncertainty of the permeability was evaluated, and the total uncertainty of the permeability is about 5.87%The results show that the introduction of reference chamber can mitigate the influence of the residual pressure in the measurement chamber. This new method allows simplified and visualized measurement of the permeation fluxes.