X-ray diffraction and molecular dynamics simulations were used to probe the structures of two families of ionic liquids containing oligoether tails on the cations. Imidazolium and pyrrolidinium bis(trifluoromethylsulfonyl)amide ILs with side chains ranging from 4 to 10 atoms in length, including both linear alkyl and oligo-ethylene oxide tails, were prepared. Their physical properties, such as viscosity, conductivity and thermal profile, were measured and compared for systematic trends. Consistent with earlier literature, a single ether substituent substantially decreases the viscosity of pyrrolidinium and imidazolium ILs compared to their alkyl congeners. Remarkably, as the number of ether units in the pyrrolidinium ILs increases there is hardly any increase in the viscosity, in contrast to alkylpyrrolidinium ILs where the viscosity increases steadily with chain length. Viscosities of imidazolium ether ILs increase with chain length but always remain well below their alkyl congeners. To complement the experimentally determined properties, molecular dynamics simulations were run on the two ILs with the longest ether chains. The results point to specific aspects that could be useful for researchers designing ILs for specific applications. The focus of the ionic liquid (IL) community is shifting beyond the mere measurement of physical properties and identification of trends arising from particular structural moieties. Researchers are delving deeper into the nanostructural interactions between the ions to determine the topographical landscape of the ions within the liquids that influence IL properties.1-3 Such information is valuable when tuning the properties of ILs for particular applications. The ability to tune the properties of ionic liquids for specific applications is a major factor in their allure as remarkable solvents that make it possible to do extreme chemistry without extreme conditions. It has been acknowledged that although ionic liquids have a combination of physical properties that make them attractive alternatives to traditional solvents, they have relatively high viscosities that hamper their practical application in large-scale processes. For example, in the area of electrochemical energy storage devices there is still an urgent need for improved electrolytes exhibiting properties of combustion resistance, high conductivity, and wide electrochemical windows. ILs with improved transport properties (viscosity, conductivity and diffusivity) would be perfect candidates to address this need. Structural modification of the IL cation and anion is a proven tool to dramatically alter IL properties. In particular, substituting ether functionalities for alkyl functionalities on IL cations has been shown to reduce the viscosity of ionic liquids significantly.2,4-6 In this work we examine the effect of incorporating oligoether side chains of varying lengths (1-3 repeating ethoxy units, Figure 1) on the physical properties and structural characteristics of imidazolium and pyrrolidinium NTf 2 ionic liquids in ...

No abstract

The radiolytic production of molecular hydrogen in the ionic liquids N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide ([N1114][Tf2N]) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) has been examined with γ-rays, 2-10 MeV protons, and 5-20 MeV helium ions to determine the functional dependence of the yield on particle track structure. Molecular hydrogen is the dominant gaseous radiolysis product from these ionic liquids, and the yields with γ-rays are 0.73 and 0.098 molecules per 100 eV of energy absorbed for [N1114][Tf2N] and [emim][Tf2N], respectively. These low yields are consistent with the relative insensitivity of most aromatic compounds to radiation. However, the molecular hydrogen yields increase considerably on going from γ-rays to protons to helium ions with [emim][Tf2N] while they remain essentially constant for [N1114][Tf2N]. FTIR and UV-vis spectroscopic studies show slight degradation of the ionic liquids with radiation.

The dodecane radical cation reaction rate constant with CMPO was measured using ps electron pulse radiolysis/ absorption spectroscopy as k = (1.30 ± 0.11) 9 10 10 M -1 s -1 in dodecane/0.10 M CH 2 Cl 2 solution. No reactivity increase occurred when these solutions were pre-contacted with nitric acid, similar to the behavior observed for TODGA. To corroborate these kinetic data with steady-state radiolysis measurements, where acid pre-contacted CMPO showed significantly less degradation, it is proposed that the dodecane radical cation always reacts directly with TODGA, but for CMPO the charge-transfer occurs with the CMPOÁHNO 3 complex formed in the acid contacted solvent.

A variety of imidazolium, quaternary ammonium, and phosphonium cation based ionic liquids were irradiated with -rays, 2-15 MeV protons and 5-20 MeV helium ions in order to examine their relative radiation stability and potential hazards for application in advanced nuclear fuel cycles. Molecular hydrogen production can be taken as an overall indicator of radiation stability, and was found to be considerably lower for the -irradiated aromatic imidazolium based compounds when compared to the other aliphatic based media. Increasing the length of the aliphatic side chain increases the H 2 yields for all the compounds examined. Little difference is found in the production of H 2 between the quaternary ammonium and phosphonium based ionic liquids with similar length side chains. Yields of H 2 increase substantially from rays to 5 MeV He ions for the imidazolium based ionic liquids, but little variation with radiation type is observed for the quaternary ammonium and phosphonium based ionic liquids. The imidazolium based ionic liquids show a darkening with increasing dose and the UV-visible spectra show an increase in absorption from 240 to 400 nm that is probably due to induced changes in the cation. FTIR spectra show little variation with radiolysis, which is consistent with the low H 2 yields. The formation of a new peak at 1658 cm-1 is attributable to the formation of acyclic disubstituted alkene bonds in the irradiated imidazolium based compounds.