(30d) Impacts of Aminopolymer-Support Interaction on CO2 Sorption Performance Probed By Neutron Scattering Techniques

Composites of poly(ethyleneimine) (PEI) and mesoporous silica are highly effective, reversible sorbents for CO₂, both from flue gas and in direct air-capture applications. The morphology of the PEI phase and its dynamic behavior (e.g. self-diffusion) within the silica can strongly impact both the kinetics and overall carbon capture efficiency of these sorbents. Here, we directly probe the shape of the supported polymer phase as a function of fill fraction using small-angle neutron scattering (SANS) and further investigate the mobility of PEI within this phase using quasi-elastic neutron scattering (QENS). Corroborated by textural characterization from physisorption analysis, the SANS data indicate that PEI forms a conformal coating on silica pore walls at low fill fraction, while at higher fillings the polymer aggregates and forms plugs that span the pore diameter. QENS additionally indicates that interaction with the silica surface dramatically decreases center-of-mass diffusion of PEI relative to the bulk phase and, to a lesser extent, also slows side-chain mobility. Hydrophobic functionalization of the silica leads to an increase of the PEI mobility above that in native silanol-terminated silica, and is also found to yield higher CO₂ capture efficiency (amine efficiency) as well as improved sorption kinetics. Thus, this work supports the existence of a link between the affinity of the support for PEI and the accessibility of active sorbent functional groups.