4. General formalism of gas transfer in dense polymers and material selection criteria

As current industrial applications of gas permeation are almost exclusively based on membranes made from dense polymeric materials, the particularities associated with this type of structure are detailed below.

Since the transport mechanism of a gas in a dense polymer material involves a so-called solution-diffusion process, both processes will contribute to the permeability value of the gas in a given material. Under steady-state transport conditions, the flux J of a compound in a dense polymer will therefore depend on the gas' ability to dissolve in the polymer (a thermodynamic step governed by a sorption coefficientS _i in mol.m ^–3 .Pa ^–1 ) and its diffusion coefficient (D in m ² .s...