CO₂ 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.