title: Effect of water on the structure of a prototype ionic liquid.
abstract: The influence of water on the structure of a prototype ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate (C8mimBF4) is examined in the IL-rich regime using high-energy X-ray diffraction (HEXRD) and molecular dynamics (MD) simulations. A many-body polarizable force field APPLE&P was developed for C8mimBF4-water mixture. It predicts structure factors of pure IL and IL-water mixture in excellent agreement with the HEXRD experiments. The MD results provide detailed insights into the structural changes from the partial structure factors, 2-D projections of the simulation box and 3-D distribution functions. Water partitioning with IL and its competition with BF4(-) for complexing the imidazolium rings was examined. The added water molecules occupy a diffuse coordination shell around the imidazolium ring but are not present around the alkyl tail. The strong coordination of the fluorine atoms of the BF4(-) anions to the imidazolium ring is not significantly changed by the addition of water. A complementary packing of water and imidazolium around BF4(-) was found. These results are consistent with the very small differences in the average structure between the pure IL and the mixture.
authors.affiliation: Electrochemistry Branch, Sensor and Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, MD 20783, USA.
authors.forename: Oleg
authors.initials: O
authors.lastname: Borodin
authors.forename: David L
authors.initials: DL
authors.lastname: Price
authors.forename: Bachir
authors.initials: B
authors.lastname: Aoun
authors.forename: Miguel A
authors.initials: MA
authors.lastname: González
authors.forename: Justin B
authors.initials: JB
authors.lastname: Hooper
authors.forename: Maiko
authors.initials: M
authors.lastname: Kofu
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohara
authors.forename: Osamu
authors.initials: O
authors.lastname: Yamamuro
authors.forename: Marie-Louise
authors.initials: ML
authors.lastname: Saboungi