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.