Doctor of Philosophy (PhD)
Deep Eutectic Solvents (DES) are liquid mixtures prepared from solids. As a new class of green solvents, DES not only share many properties with ionic liquids, such as low volatility, conductivity, tailorable constituents, but also have some advantages over ionic liquids, like easier preparation, safe and inexpensive materials, biodegradability, low toxicity, and excellent solubility. Because of those attractive properties, DES has been studied in many scientific and engineering fields. However, compared with the great number of studies of the application, many questions about structure and dynamics of DES are unanswered. To shed light on the mystery of solvent or solvation structure and dynamics, we investigated the DES systems with Fourier Transform Infrared (FTIR) and Two-Dimensional Infrared spectroscopy (2DIR). Vibrational transitions measured by infrared spectroscopy serve as sensitive probes to report the local environment and dynamics. We studied the solvation structure and dynamics of choline chloride-based DESs with thiocyanate probe. The interactions between solute and solvation shell were assigned by use of FTIR and confirmed by Molecular Dynamics (MD) simulation. The vibrational mode of infrared probes allowed detection of the solvation dynamics in choline chloride-based DESs as in-place and inter-solvation shell motions within picosecond timescale. Assignments were confirmed by the analysis of MD simulation. In another project, we studied the effects of the molecular structure of hydrogen bond acceptor on the structure and dynamics of acetamide based DES. Our studies show that symmetry of the HBA cation will affect the contribution of slow molecular motion of the environment. The overall dynamics is rationalized in terms of a microscopic heterogeneous structure of the DESs, where the heterogeneities create domains that slow making and breaking of the hydrogen bond. Heterogeneity was further supported by the use of MD simulation. Lastly, we investigated the interactions and solvent structure of a non-ionic DES composed of N-methylacetamide and lauric acid. The interactions among the components were observed with FTIR and temperature-dependent experiments. Finally, the heterogeneous structure of DES with polar and non-polar domains was proposed, and verified by observed confined dynamics of amide band and probes, which is similar to reported water dynamics in reverse micelles.
Cui, Yaowen, "Investigation of Structure and Dynamics of Deep Eutectic Solvent Using Infrared Spectroscopy" (2018). LSU Doctoral Dissertations. 4616.