Structural Investigation of Quaternary Ammonium-Functionalized Networks for Gas Capture Applications

As society moves to reduce the effects of climate change, there is a growing needfor the use of polymer science in technologies to mitigate the emission of carbon dioxide. Networks containing quaternary ammonium groups with corresponding HCO3 ions providing the mobile counter-charge in the networks have been reported to capture carbon dioxide directly from the atmosphere through a moisture swing mechanism, among other mechanisms. In this work, microstructural analysis of synthesized polystyrene-based anion exchange networks is conducted using known characterization techniques to better understand if variations in sorbent microstructure adjust the distances between the quaternary ammonium groups. Additional surface morphology studies of these sorbents are conducted. X-Ray Diffraction (XRD) spectra reveal the amorphous structure of these polymers and the ability to adjust the distance between quaternary ammonium groups by introducing different spacer groups and various anions into the networks, which may affect the spontaneity of the CO2 to chemisorb to these sorbents. However, Wide Angle X-Ray Scattering (WAXS) conflicts with the XRD data, indicating a change in distance between these groups is not achieved. Additionally, WAXS data indicates an ability to increase the homogeneity of structure in these materials by introducing larger counterions into the networks. Small Angle X-Ray Scattering (SAXS) reveals no obvious large morphological features in these sorbents, which is supported by Scanning Electron Microscopy (SEM) images. In conclusion, XRD and WAXS experiments exhibit conflicting data regarding the ability to adjust the distances between the quaternary ammonium groups in these networks. Proposed actions to resolve this conflict are presented. Finally, SEM sheds light on particle size and morphological features of these materials.