Activation Entropy for Diffusion of Gases Through Mixed Matrix Membranes

Diffusion in a polymeric membrane, according to the transition activated complex of Eyring, is described within the thermodynamic frame by two terms; one is the activation energy and the other the activation entropy. Both contributions describe to the membrane as barriers in series. Particularly, the activation energy is the high of such barriers, and is related to the enthalpic selectivity. It depends on the cohesive energy of the polymer and the kinetic radius of the particles. Whereas, the entropic selectivity is related to the necessary change of entropy to surmount the barrier, implying a change in the disorder at both side of the barrier or a change in the internal degree of freedom of the diffusive molecules, as in the example of the dioxide of carbon to go through the barriers of the membrane.