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 ...

Ionic liquids (ILs) with relatively low viscosities and broad windows of electrochemical stability are often constructed by pairing asymmetric cations with bisfluorosulfonylimide (FSI−) or bistriflimide (NTf2 −) anions. In this work, we systematically studied the structures of ILs with these anions and related perfluorobis-sulfonylimide anions with asymmetry and/or longer chains: (fluorosulfonyl)(trifluoromethylsulfonyl)imide (BSI0,1−), bis(pentafluoroethylsulfonyl)imide (BETI−), and (trifluoromethylsulfonyl) (nonafluorobutylsulfonyl)imide (BSI1,4−) using high energy X-ray scattering and molecular dynamics simulation methods. 1-alkyl-3-methylimidazolium cations with shorter (ethyl, Im2,1+) and longer (octyl, Im1,8+) hydrocarbon chains were selected to examine how the sizes of nonpolar hydrocarbon and fluorous chains affect IL structures and properties. In comparison with these, we also computationally explored the structure of ionic liquids with anions having longer fluorinated tails.

Dicationic ionic liquids (DILs) of diverse structural architectures (including symmetrical and asymmetrical ammonium, phosphonium and heterodications and the bis(trifluoromethylsulfonyl)amide (NTf 2 − ) anion) have been prepared and used as additives to N-methyl-N-ethoxyethylpyrrolidinium (P 1 EOE) NTf 2 , a relatively high-performing IL in terms of its transport properties (viscosity 53 mPa s). The three-ion, binary IL mixtures were characterized for their thermal and transport properties using differential scanning calorimetry, temperature dependent viscosity, conductivity and Pulsed Gradient Spin Echo (PGSE) NMR. Variable temperature 1 H, 19 F and 31 P self-diffusion coefficients were determined at 25, 60 and 75 • C. The order of the diffusion coefficients was D(, and the composition of the dication had a strong effect on the degree to which diffusion of all three species is more or less coupled. IL mixtures containing about 30 mol % of the dicationic NTf 2 and 70 mol % of P 1 EOE NTf 2 resulted in a significant decrease in glass transition temperatures and viscosities compared to the pure DIL. The mixtures extended the liquid range and potential for practical applications significantly. The data obtained here provides insight into the future design of dicationic salts tailored to exhibit lower viscosity and higher conductivities.