title: Supramolecular structure fluctuations of an imidazolium-based protic ionic liquid.
abstract: At 20, 25, 30, and 40 °C, the ultrasonic absorption spectra of the protic ionic liquid 3-(butoxymethyl)-1H-imidazol-3-ium salicylate have been measured between 0.6 and 900 MHz. Below 250 MHz, the absorption coefficient decreases with temperature, potentially indicating a major effect of the viscosity and/or a relaxation time. Essentially the broad spectra can be favorably represented by two relaxation terms in addition to an asymptotic high-frequency contribution. One term reflects an asymmetric relaxation time distribution. It is described by a model of noncritical fluctuations in the structure and thermodynamic parameters of the liquid in order to yield the fluctuation correlation length and the mutual diffusion coefficient. Applying the Stokes-Einstein-Kawasaki-Ferrell relation, these quantities can be used to show that the effective shear viscosity controlling the fluctuations is substantially smaller than the steady-state shear viscosity. This result is consistent with dispersion in the shear viscosity as revealed by viscosity measurements at 25, 55, and 81 MHz. The other term can be well described by a Debye-type relaxation function. It has been tentatively assigned to a structural isomerization of the butoxymethyl chain of the imidazole molecule. However, it cannot be completely excluded that this term reflects, at least in parts, a Brønstedt acid-base equilibrium or a specific association process.
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Edward
authors.initials: E
authors.lastname: Zorębski
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Michał
authors.initials: M
authors.lastname: Zorębski
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Marzena
authors.initials: M
authors.lastname: Dzida
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Lodowski
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kowalska-Szojda
authors.forename: Joanna
authors.initials: J
authors.lastname: Feder-Kubis
authors.affiliation: Department of Engineering Physics, Tashkent State Technical University, Do'rmon Yuli 33, 100125 Tashkent, Uzbekistan.
authors.forename: Sirojiddin Z
authors.identifier: 0000000322969624
authors.initials: SZ
authors.lastname: Mirzaev
authors.affiliation: Universität Göttingen, Drittes Physikalisches Institut, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany.
authors.forename: Udo
authors.initials: U
authors.lastname: Kaatze