By combining experiments and computation, our studies of bulk ILs and their interactions at vacuum and solid interfaces will provide valuable information for materials design. The primary relevance may be to energy storage materials for next generation studies batteries and electrical double-layer capacitors. Recent work in our labs and with our collaborators includes experimental and computation studies of ionic liquids (ILs). Results include measurements of the liquid structure functions S(q) using high-energy X-ray scattering, which are quantitatively compared with the same observable calculated from molecular dynamics simulations. Our focus is on understanding liquid with less common functionalities, such as hydrophobic branched alkyl chains on the cations, or substitution of these branched side groups with more polar alkylsiloxy groups. Studies of the liquid order at the vacuum-IL interface are accomplished by molecular simulations that are compared with angle-resolved X-ray photoelectron spectroscopy (XPS) measurements. By detecting the photoelectrons at steep emergence angles up to 85°, surface profiling of the top 1 nm of the vacuum-IL is achieved. Use of a combination of electron spectroscopies permits detailed studies of ultrathin IL films ranging from 1 monolayer to 10 or more multilayers. XPS measurements provide the core electron binding energies, while the HOMO, LUMO and vacuum energies are obtained by combining ultraviolet photoelectron and inverse photoelectron spectroscopies.

Molecular geometries and electronic structures of ionic liquids: Bulk, vacuum interfaces, and ultrathin films

253rd National Meeting (2017)

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