Ultrafast Vibrational Spectroscopy of Carbon Dioxide in Polymers and Ionic Liquid-Polymer Composite MaterialsKelsheimer, C. J. (2021) Ultrafast Vibrational Spectroscopy of Carbon Dioxide in Polymers and Ionic Liquid-Polymer Composite Materials. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractUltrafast two-dimensional infrared spectroscopy enables measurement of frequency dynamics and inter- and intramolecular kinetics which report motions on femto- to picosecond timescales, and angstrom length scales. These measurements are used herein to investigate carbon dioxide's interaction with ionic liquids, polymers and ionic liquid-polymer composite materials. These systems are of interest for carbon capture and storage utility, an important step of curbing greenhouse gas emissions. In an investigation of carbon dioxide in a poly(ethylene glycol) diacrylate gel an unexpected hot ground state is reproducibly measured, and the model used to describe the intramolecular landscape of carbon dioxide is expanded as a result. Polarization-controlled ultrafast experiments are used to measure anisotropy and investigate the two-dimensional frequency dependence in a representative composite material. Spectra are taken of carbon dioxide in a pair of structurally isomeric, high molecular weight polymers. Poly(vinyl acetate) and Poly(methyl acrylate) show different cloud point behavior despite being nearly identical. While their frequency fluctuation dynamics were not meaningfully different, their intramolecular kinetics were distinctly different, lending weight to direct interaction with the polymer side chains as the cause of different cloud point behavior. Finally, carbon dioxide in a volume percent series of ion gels is measured. These show a nonlinear, non-monotonic relationship between the timescales of structural reorganization and the percent by volume ionic liquid. A three-regime, core-shell-matrix type model is proposed and suggested as an explanation for this odd behavior, which reproduces the pattern of the data well. This work offers a perspective on the question of carbon dioxide's interaction with carbon capture media, and identifies important intra- and intermolecular processes that may govern this relationship. The work herein lays groundwork for further studies of ultrafast two-dimensional vibrational spectroscopy in composites, gels, polymers, and other solid materials, along with expanding the analytical tools to understand these interactions. Share
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