Glenn Hefter

The protic ionic liquid ethylammonium nitrate [EtNH3+][NO3–] (EAN) can in some ways be considered as an archetypal IL. Certainly, since its first investigation 100 years ago by Walden, it is one of the best known. The study of the dynamics of EAN, with its relatively simple structure, provides an opportunity to better understand the behaviour of more complex ILs. However, there is another reason why EAN warrants special attention: this is because it has been proposed as an analogue of that truly mysterious but very important substance dihydrogen monoxide (aka water). The basis for this claim is an apparent similarity between various H-bonding modes that are observed in the far-infrared (THz) region of both substances. However, such spectra are difficult to measure and even more difficult to interpret without detailed knowledge of other possible modes that might exist in this spectral region. This talk will describe the dynamics of EAN and some closely-related compounds over the extraordinarily wide frequency range from 200 MHz to 10 THz (~350 cm–1) obtained by using a combination of dielectric relaxation and optical Kerr-effect spectroscopies. Detailed analysis of these spectra shows that the observed intensities are actually a complex combination of overlapping and probably coupled modes, including H-bond vibrations, cation and anion librations and possibly other cooperative effects; the relationships between EAN and water are not clear-cut.

Reliable solubility data for oxides and hydroxides of heavy metals in alkaline solutions are relevant to a number of industrial and geochemical processes, including the production of high-purity alumina in the Bayer process, the formation of ores from geothermal solutions at high pH, hydrometallurgical leaching processes for the extraction of metal values from ores and plant residues, and the storage and processing of certain types of radioactive waste. Recent results obtained for various systems will be reported, including experimental and modelling aspects. A new facility for the storage, handling and processing of solubility data will be outlined.

To exploit the great potential of room-temperature ionic liquids (RTILs) as solvents that offer both low environmental impact and product selectivity, an understanding of the liquid structure, the microscopic dynamics, and the way in which the pertinent macroscopic properties, such as viscosity, thermal conductivity, ionic diffusion, and solvation dynamics depend on these properties, is essential. We have measured the intermolecular dynamics of the 1,3-dialkylimidazoliumbased RTILs [emim][BF4], [emim][DCA], and [bmim][DCA], at 25 °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. In the terahertz region, the signal-to-noise ratio of the OKE spectra is particularly high and the data show that there is a greater number of librational and intermolecular vibrational modes than previously detected. Of greatest interest though, is an intense low frequency (sub-alpha) relaxation that we show is in strong accordance with recent simulations that observe mesoscopic structure arising from aggregates or clusters; structure that explains the anomalous and inconveniently-high viscosities of these liquids.

Accurate values of the pressure and temperature dependence of the static permittivity (dielectric constant), ε, are of great scientific interest, since they are required for the application of various theories. For instance, the pressure dependence of ε needs to be known to model the compression of a solvent by the electric field of an ion via the Drude-Nernst equation,1 or to apply the Debye-Hückel limiting law to heat capacities and volumetric properties.2 However, studies of ε(p,T) of molecular solvents in the literature are scarce.3 A three-lobed re-entrant radio-frequency resonator with vacuum resonance frequencies of approximately (170, 675, and 1130) MHz has been used to measure ε(p,T) for two common solvents N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The permittivity was measured in the temperature range of 5 °C to 55 °C for DMF and 20 °C to 55 °C for DMSO in a pressure range of (1 to 50) bar. However, the first resonance frequency was below the low-frequency limit of the current instrumentation and the third one was overlapped by higher modes for the two solvents. Therefore ε(p,T) was only accessible from the second mode at ~100 MHz. The third resonance was used to cross-check the dε/dp value.