Effect of Film Thickness and Temperature on the CO₂ Sorption in Poly(ethyleneimine)

Poly(ethyleneimine) (PEI) is an attractive material for CO₂ soprtion due to its high amine content (1 nitrogen for every 2 carbons). Hyperbranched PEI, specifically, is appealing due to its low glass transition temperature (T_g), which facilitates diffusion of CO₂ through the polymer. However, due to its low T_g hyperbranched PEI is typically imbibed into porous silicates to form a solid sorbent material. This coating process, while practical, leads to poorly defined PEI film thickness and local variations in PEI concentrations within the porous support. In an effort to understand fundamental aspects of CO₂ uptake and release, we proposed to study planar PEI thin films, which allows us to explore the effect of film thickness on CO₂ sorption. In this presentation, I will discuss our measurements of adsorption/desorption at a function of temperature, humidity, and CO₂ concentration for different PEI film thicknesses using tandem quartz crystal microbalance (QCM) and polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS). Coupling these techniques allows for quantification of mass uptake via QCM and spectral identification of reaction products via FTIR.