Curvature Effect in Polydimethylsiloxane Interaction with CO₂. Insights from Theory

In this study we employ density functional theory to investigate the binding interaction between polydimethylsiloxane and CO₂ for application in gas separation membranes. The binding strength has been studied systematically as a function of the monomer conformational rotations in the polymer chain. Our work identified major differences between the CO₂ interaction with the helical conformation and the linear conformation of polydimethylsiloxane polymer chains. We have further estimated dependence between the CO₂ binding strength and the polydimethylsiloxane polymer chain curvature by systematically evaluating the CO₂ binding to cyclic polydimethylsiloxane oligomers. The enhanced CO₂ interaction with helical chains and cyclic oligomers was attributed to cooperative, confinement effects, and local electron density distribution at the Si-O-Si fragments. The binding modes were identified using vibration frequency analysis.