Towards an empirical model for the prediction of the selectivity of polymer membranes

Polymer membranes are often used in combination with gas sensors for selectivity enhancement, especially with metal-oxide sensors (MOX). We report on the development of an empirical model to predict the gas separation properties of polymer membranes. This model is based on the two parameters sorption and diffusion, represented by the polar fraction of the free surface energy (SFE), and the water absorption combined with the molecule diameter based on Lennard-Jones. We measured the surface tension for a number of common fluoropolymers and used the results to determine their SFE using the graphical method developed by van Oss-Chaudhury-Good, compared them with literature data and further optimized the model. With the optimized model, combined with the information on functional groups in the polymers, we are able to predict the selectivity of polymer membranes.