On the magnetic channels in polymer membranes

Abstract

In recent years we have proposed magnetic membranes (membranes with dispersed granules of a permanent magnet) for the separation of oxygen and nitrogen in the air mixture. The idea was to utilize oxygen's paramagnetic properties which are absent in the nitrogen. The experimental results were promising but they demanded a theoretical description which is given in the present paper. By a detailed analysis of the available data we arrive at four important conclusions: (1) magnetic channels are formed around the magnetic granules, (2) the channels provide high permeability “highways” for the diffusion of permeating molecules, (3) the oxygen molecules, due to their paramagnetic properties, stick to these “highways” for a longer time than the nitrogen, which is probably based on the interaction with the Weiss molecular field of the permanent magnet, (4) the magnetic field induces aggregation between oxygen and nitrogen which enhances the transport of both nitrogen and oxygen by prolonging their residence in the channel. In addition to these findings, the most suggestive theory of magnetic membrane operation is ruled out: the forcing of the oxygen molecules due to the gradients of magnetic field generated by the granules is too weak to account for the observed effects.