title: Dielectric relaxation and solvation dynamics in a prototypical ionic liquid + dipolar protic liquid mixture: 1-butyl-3-methylimidazolium tetrafluoroborate + water.
abstract: Dielectric and solvation data on mixtures of 1-butyl-3-methylimidazilium tetrafluoroborate ([Im41][BF4]) + water are reported and used to examine the utility of dielectric solvation models. Dielectric permittivity and loss spectra (25 °C) were recorded over the frequency range 200 MHz to 89 GHz at 17 compositions and fit to a 4-Debye form. Dynamic Stokes shift measurements on the solute coumarin 153 (C153), made by combining fluorescence upconversion (80 fs resolution) and time-correlated single photon counting data (20 ns range), were used to determine the solvation response at 7 compositions (20.5 °C). All properties measured here were found to depend upon mixture composition in a simple continuous manner, especially when viewed in terms of volume fraction. Solvation response functions predicted by a simple dielectric continuum model are similar to but ∼7-fold faster than the spectral response functions measured with C153. The solvation data are in better agreement with the recently published predictions of a semimolecular model of Biswas and co-workers [J. Phys. Chem. B 2011, 115, 4011], but these latter predictions are systematically slow by a factor of ∼3.
authors.affiliation: Department of Physics, Nankai University , Tianjin, China.
authors.forename: Xin-Xing
authors.initials: XX
authors.lastname: Zhang
authors.forename: Min
authors.initials: M
authors.lastname: Liang
authors.forename: Johannes
authors.initials: J
authors.lastname: Hunger
authors.forename: Richard
authors.initials: R
authors.lastname: Buchner
authors.forename: Mark
authors.initials: M
authors.lastname: Maroncelli