Modeling Adsorption and Transport Properties of Gases in Amorphous Polymers

Developing greener and more cost-effective polymer membranes for gas separation is of major interest within the industry of gas purification, in particular with regard to H₂ separation. Present findings suggest that fluorinated membranes are a promising medium for H₂ gas selective separations. In this work, molecular modeling was used to aid experimental efforts to optimize fluorinated polymer membranes for high H₂ permeability selectivity. Permeability is comprised of the product of solubility and diffusivity, both of which are easily accessible computationally. To guide a detailed understanding of this behavior a molecular-level approach has been applied with both Monte Carlo and molecular dynamics simulation. Gibbs-Ensemble Monte Carlo was used to calculate gas solubility and allowed for the determination of preferred adsorption sites within the polymer systems. Molecular dynamics simulation was then used to calculate rates of gas self-diffusion with each polymer studied. The fluorinated polymers examined in this study also possess differing tacticities whose unique structures were examined in hopes that they may offer an additional degree of freedom for polymer optimization. Gaining an understanding of these processes on a molecular level will help guide the optimization of polymer structures and conditions needed to develop efficient separation membranes.