Molecular dynamics simulations of the interactions between CO2 and branched unreacted and reacted polyethylenimine films

One of the most promising technologies to capture CO2 molecules directly from ambient air involves a polyethylenimine (PEI) layer deposited on a microporous solid support. The CO2 adsorption is achieved through a chemisorption process in which CO2 molecules react with amine groups of the polymer. This process was widely investigated from an experimental front point of view and accordingly once the reaction occurred, the further diffusion of CO2 molecules within this layer is heavily hindered. The aim of this study is to elucidate this phenomenon from a nanoscale perspective through molecular dynamics simulations. Starting from a branched unreacted PEI chain and a branched reacted PEI chain, three different systems were generated by arranging these two compounds in different configurations. Simulation results highlighted that the CO2 molecules are more prone to interact with the branched reacted PEI chains because of the higher electrostatic attraction. As a consequence, their further diffusion towards the unreacted region, where Coulombic interactions are weaker, is strongly hindered and it remains unexploited.