Permeability of Polymers

Virtually all the membrane processes realized for separation of gases and vapors employ non‐porous polymeric membranes. The solution–diffusion mechanism provides an overall principle of the mass transfer through non‐porous polymer membranes. However, in depth understanding of the mechanism of gas transport is impossible without more detailed, desirably atomistic models of what occurs when gas molecules are dissolved in polymers and diffuse through polymer films or membranes. Two approaches can serve for this aim: transition‐state model and free volume model Gas sorption is the driving force of transport in non‐porous polymer membranes, so thermodynamics of gas sorption in polymers is very important issue. When the concentration of dissolved penetrants in a polymer is low, they only weakly influence the properties of the polymer matrix. The solubility coefficients in the absence of specific interactions between the diffusing molecules and polymer matrix are determined by the van der Waals interactions.