Ionic liquid interfaces: an X-ray photoemission spectroscopy perspective
Date
2018
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Publisher
University of Delaware
Abstract
The evolution of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) in recent years has allowed for the investigation of ionic liquid interfaces in the presence of a gas phase. In this thesis the vacuum structure and effects of water vapor on the interface of ionic liquids of interest are examined. There are three systems considered in this dissertation, namely, water interactions with a hydrophobic ionic liquid, water interactions with a hydrophilic system, and lastly the unique structuring that exists within an ionic liquid mixture containing both hydrophobic and hydrophilic anions with the same imidazolium-based cation. The total electron scattering cross-section at various kinetic energies was calculated from the hydrophobic ionic liquid [EMIM][Tf2N]. For the hydrophilic ionic liquid system, the mole fraction of water and its inherent enhancement on the interface relative to the bulk was quantitatively assessed. In regard to the ionic liquid mixture the partitioning behavior of the hydrophobic anion at the surface was quantitatively calculated via angle resolved XPS (AR-XPS) using a simple methodology to probe vacuum-compatible liquids at a surface-sensitive grazing angle. Furthermore, the effect of water vapor on the ionic liquid mixture surface structure was quantitatively explored.