CO ₂ Transport Behavior in Perfluoropolyether Elastomers for Gas Separation Applications

Fluoropolymer membranes offer exceptional chemical stability for gas separation but face a fundamental permeability-selectivity trade-off that limits their performance in applications such as CO2 capture and natural gas purification. This study systematically examines CO2 transport behavior in perfluoropolyether (PFPE) elastomers─a class of high-permeability fluoropolymers─and their silica-filled composites to understand how filler incorporation can overcome this limitation. Using time-resolved attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and quartz crystal microbalance (QCM), we quantified CO2 diffusivity and solubility across a range of concentrations. The neat PFPE elastomer exhibits exceptionally high CO2 permeability (1218 Barrer) characteristic of rubbery fluoropolymers with low glass transition temperature (−52 °C). The results reveal that silica incorporation (8.5 wt %) increases CO2 sorption capacity by 21% (from 15.10 to 18.35 mg/g·atm) while simultaneously improving CO2/N2 selectivity from 5.8 to 7.2 with only a 4.4% reduction in CO2 permeability (to 1164 Barrer). The enhancement in selectivity is attributed to increased tortuosity that preferentially impedes N2 diffusion, while the improved sorption results from interfacial free volume created by well-dispersed silica nanoparticles. These findings demonstrate a viable strategy for tuning PFPE-based membrane performance for CO2/N2 separation applications.