Ultrafast Vibrational Spectroscopy (2D-IR) of Carbon Dioxide in Ionic Liquid-Polymer Composite Materials

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AbstractIn this project, funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program of the Chemistry Division, Professor Sean Garrett-Roe’s laboratory at the University of Pittsburgh is using lasers to study how new types of materials could be used to filter out unwanted carbon dioxide that is given off by power plants, before it reaches the atmosphere. This could be much less expensive than other current methods. These materials could, for example, contain salts that are liquid at room temperature (ionic liquids) within the structure of plastic membranes. One of the aims of Professor Garrett-Roe’s project is to understand how to optimize the interactions of carbon dioxide molecules with the new materials. The project is determining the structures of the ionic liquids within the plastic membranes and using that information to model the chemical features that control how carbon dioxide moves through the materials. Parallel to the research, the grant supports the training of graduate students in interdisciplinary scientific areas. Two undergraduates per year from a historically black undergraduate institution visit for summer research opportunities. In addition, the project develops teaching infrastructure, specifically an online platform for teachers to develop, share, and get feedback on new POGIL (Process Oriented Guided Inquiry Learning) activities.The specific goal of this project is to understand carbon dioxide solvation in composites of ionic liquids and cross-linked poly(ethylene glycol) diacrylate (PEGDA). The project uses ultrafast vibrational spectroscopy (2D-IR) on the antisymmetric stretch of the carbon dioxide to report the structure and dynamics of carbon dioxide's local solvation environment. The work tests the hypothesis that the solvation environment of carbon dioxide is dominated by the anions of the ionic liquid, and that the polymer matrix slows dynamics by increasing the entropy of activation for reorganizing a solvent shell. The test of the hypothesis has three components: (1) to determine the structures of the ionic liquid in the ionic liquid - PEGDA ion gels with a suite of tools, including atomic force microscopy, polarized light microscopy, and scanning electron microscopy, covering length scales from tens of nanometers to microns; (2) to test a core-shell-matrix model of solvation dynamics by recording 2D-IR spectra as a function of ionic liquid volume percent; and (3) to determine the activation energies of bulk thermodynamics and transport (solubility, diffusivity, and permeability) as well as specific molecular dynamics (structural and rotational spectral diffusion). This project advances 2D-IR spectroscopy by demonstrating a temperature- and polarization-resolved approach to separate the activation energies related to motion of the vibrational chromophore and the surrounding solvent. The research supports important goals in advancing the nation's ability to compete in the global, high-technology economy by providing the fundamental understanding needed to develop next generation materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.