title: Dynamics of imidazolium ionic liquids from a combined dielectric relaxation and optical Kerr effect study: evidence for mesoscopic aggregation.
abstract: We have measured the intermolecular dynamics of the 1,3-dialkylimidazolium-based room-temperature ionic liquids (RTILs) [emim][BF(4)], [emim][DCA], and [bmim][DCA] at 25 degrees C from below 1 GHz to 10 THz by ultrafast optical Kerr effect (OKE) spectroscopy and dielectric relaxation spectroscopy (DRS) augmented by time-domain terahertz and far-infrared FTIR spectroscopy. This concerted approach allows a more detailed analysis to be made of the relatively featureless terahertz region, where the higher frequency diffusional modes are strongly overlapped with librations and intermolecular vibrations. Of greatest interest though, is an intense low frequency (sub-alpha) relaxation that we show is in accordance with recent simulations that have reported mesoscopic structure arising from aggregates or clusters--structure that explains the anomalous and inconveniently high viscosities of these liquids.
authors: Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, UK. david.turton@phys.strath.ac.uk
authors: David A
authors: DA
authors: Turton
authors: Johannes
authors: J
authors: Hunger
authors: Alexander
authors: A
authors: Stoppa
authors: Glenn
authors: G
authors: Hefter
authors: Andreas
authors: A
authors: Thoman
authors: Markus
authors: M
authors: Walther
authors: Richard
authors: R
authors: Buchner
authors: Klaas
authors: K
authors: Wynne