Text

theses

Studies of interfacial and electronic structure properties of Ionic Liquids (ILs) may lead to development of new electrolyte-electrode systems and thin film applications, and optimize the electrochemical performance of ILs. The composition of the cations and anions, and nature of the solid substrate influences ordering at solid-liquid and vacuum-liquid interfaces. The relationship between IL composition and electronic structure may provide new insight into the nature of frontier orbitals. The interface of 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide with Au(111) and Cu(100) was characterized with scanning tunneling microscopy, X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy. The first monolayer of IL on each surface was examined in terms of adsorption strength, ion mobility, ion ordering, molecular orientation, and dissociative products. The IL deposited on Au(111) was weakly interacting and ions were mobile at room temperature. In contrast, the same IL adsorbed on Cu(100) formed a more strongly bound monolayer. The microscopy and spectroscopic methods employed were consistent in proposing an interfacial model where the IL does not decompose on copper, but the attraction was more complex than simple physisorption. The vacuum-liquid interface of silicon functionalized ILs was examined using angle resolved X-ray photoemission spectroscopy. The analysis of IL composition probing different sample depths was used to develop models of their vacuum-liquid interface. The eight ILs with shorter and longer with cation and anion chain length, chain substitution, and ring type (imidazolium or pyrrolidinium cation) were related to enhancement of less-polar groups at the top interface. Most of these novel functionalized ILs preferentially order into non-polar and polar domains at the interface, although their structures were branched and somewhat polar (silyl or siloxy chains). The electronic structure of functionalized ILs was determined using ultraviolet photoemission and inverse photoemission, probing the occupied and unoccupied states. The nature of the energy gap of the frontier orbitals of ILs were determined experimentally and interpreted from density of states calculations of isolated ions and ion pairs. Relatively simple calculations based on a pair of ions produced features that were well represented in the experimental valence band spectra of thick IL films.

ETD_7730

Ph.D.

Includes bibliographical references

by Aleksandra Barbara Biedron

doi:10.7282/T3NP26QJ

ETD doctoral

The author owns the copyright to this work.