Gas Transport Properties of Vinylidene Fluoride-Tetrafluoroethylene Copolymers

Effect of the content of tetrafluoroethylene groups on the gas transport properties of vinylidene fluoride-tetrafluoroethylene copolymers has been studied. The experimental values of permeability coefficients P and diffusion coefficients D for gases H₂, He, N₂, O₂, and CO₂ as well as lower hydrocarbons CH₄, C₂H₄, and C₂H₆ are measured, and their solubility coefficients S are calculated. It is shown that the values of the solubility coefficients of СО₂ and С₂Н₄ deviate from the direct correlation dependence of lоg S on the Lennard-Jones potential, and this effect is explained in terms of facilitated transport models. It is demonstrated that an increase in the content of TFE groups leads to a significant rise in the permeability coefficients of the studied penetrants mainly due to an increase in their diffusion coefficients. For example, the permeability coefficient of helium and hydrogen increases by almost 2.5 times, carbon dioxide by 3 times, argon, oxygen, methane and ethylene by 3.5 times, and nitrogen and ethane by 4.4 times, respectively. These gas separation parameters in combination with good film-forming properties and commercial availability make it possible to consider the studied VDF-TFE copolymers to be promising materials for the fabrication of composite gas separation membranes.