INS11-1014
Measurements of CO2 Capture in Hyperbranched PEI Thin Films
Topic
S11. PMSE–PSK50 Anniversary Symposium: Advancing Polymer Science for a Sustainable and Intelligent Future
When and Where
Sep 29, 2026
16:40 - 17:05
Room 110
Session Chairs
Myungeun SEO
Presenter(s)
Christopher M Stafford (National Institute of Standards and Technology)
Co-Author(s)
Abstract
Hyperbranched polyethyleneimine (hPEI) is a popular material for direct air capture (DAC) of CO2 (ambient pressure, 400 ppm CO2) using polymer-based solid sorbents. A deep understanding of the capture efficiency and CO2 capacity of hPEI is critically needed to optimize DAC system designs. We are developing and applying techniques to probe chemical interactions during CO2 uptake and release in PEI thin films. Specifically, we combine quartz crystal microbalance (QCM) and polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS) in a tandem cell design such that we simultaneously measure both the total mass uptake of sorbate molecules (CO2, H2O, etc.) and the chemical speciation of the resulting sorbent products, respectively, within hPEI thin films. Using this tandem cell, we investigate the effect of hPEI film thickness, temperature, CO2 concentration, and the presence of humidity on the amine efficiency of the material (mol CO2/mol N). We also hypothesize that CO2 binding to the hPEI might slow down the polymer mobility (e.g., ionic crosslinking due to carbamate groups) and thus impact further diffusion of CO2 to available amine sites. Using quasi-elastic neutron scattering (QENS) and QCM with dissipation (QCM-D), we assess the effect of CO2 binding on the extent of plasticization or densification of the polymer film upon exposure to different atmospheres. QENS, which probes local motions, shows less mobility restriction upon CO2 binding, while QCM-D, which probes large length scales, shows macroscopic polymer stiffening. Finally, we use spectroscopic ellipsometry (SE) to measure the CO2 uptake in hPEI as manifest by changes in film thickness (swelling) as a function of initial film thickness and CO2 concentration, with and without humidity. In combination, we believe that these measurements provide critical insight into the length-scale dependent CO2 capture behavior of hPEI.
