Gas Transport Properties of Vinylidene Fluoride-Tetrafluoroethylene Copolymers

Abstract

The influence of the content of tetrafluoroethylene (TFE) groups on the gas transport properties of vinylidene fluoride (VDF) and tetrafluoroethylene copolymers has been studied. Experimental values of the permeability coefficients P and diffusion coefficients D for gases H2, He, N2, O2, CO2, as well as lower hydrocarbons CH4, C2H4 and C2H6 were measured and their solubility coefficients S were calculated. The values of the solubility coefficients of CO2 and C2H4 were found to deviate from the linear correlation of lg S on the Lennard-Jones potential. An explanation of this effect was proposed based on facilitated transport models. It was demonstrated that an increase in the content of TFE groups leads to a significant increase in the permeability coefficients of the penetrants studied mainly due to an increase in their diffusion coefficients. So, the permeability coefficient of helium and hydrogen increases approximately in 2.5 times, for carbon dioxide in 3 times, for argon, oxygen, methane and ethylene in 3.5 times, and for nitrogen and ethane in 4.4 times, respectively. These gas separation parameters in combination with good film-forming properties and commercial availability allows us to consider the studied VDF-TFE copolymers as promising materials for the fabrication of composite gas separation membranes.