The polarities of a wide range of ionic liquids have been determined using the Kamlet-Taft empirical polarity scales α, β and π*, with the dye set Reichardt's Dye, N,N-diethyl-4-nitroaniline and 4-nitroaniline. These have been compared to measurements of these parameters with different dye sets and to different polarity scales. The results emphasise the importance of recognising the role that the nature of the solute plays in determining these scales. It is particularly noted that polarity scales based upon charged solutes can give very different values for the polarity of ionic liquids compared to those based upon neutral probes. Finally, the effects of commonplace impurities in ionic liquids are reported.

In this paper we use ab initio theoretical methods in combination with experimental studies to investigate ion-pairs of the ionic liquid (IL) 1-methyl-3-pentamethyldisiloxymethylimidazolium chloride [(SiOSi)C(1)C(1)im]Cl, in order to deepen our understanding of the effects of functionalisation on an IL. In addition, we focus on the effect of the siloxy group on the viscosity. We establish that the ion-pairing energies of [(SiOSi)C(1)C(1)im]Cl are similar to those of 1-butyl-3-methylimidazolium chloride [C(4)C(1)im]Cl, because the anion interacts primarily with the imidazolium ring. A large range of ion-pair structural configurations is possible with different anion positions and chain orientations, contributing to a significant entropy. A H-bonded network forms, however the siloxy chain can shield the Cl(-) or key C-H sites thus introducing defects. Despite a significant increase in mass relative to [C(4)C(1)im](+), the combined barriers to rotation within the substituent chain are substantially reduced in [(SiOSi)C(1)C(1)im](+), this is primarily due to the flexibility of the siloxane linkage, and free rotation of the Si-Me methyl groups. The most important effect is a coupling of rotational motions within the chain which leads to dynamic inter-conversion of cation conformers, and facilitates movement of the anion around the cation, these will contribute to enhanced transport properties and a reduced viscosity. In addition, a longer charge arm is expected to enhance rotational and rotational-translational coupling in electric fields. Thus, for [(SiOSi)C(1)C(1)im]Cl ion-pair association is very similar to that of [C(4)C(1)im]Cl, but "dynamic" properties relating to torsional motion, a dynamic H-bonded network, and cation response to an external electric field are enhanced.

Two new ionic liquids (ILs) with siloxane-functionalized cations and the weakly coordinating tetraalkoxyaluminate [Al(hfip)(4)](-) (hfip=hexafluoroisopropoxy) are prepared and characterized by nuclear magnetic resonance (NMR), infrared (IR) and Raman spectroscopy. With melting points below 0 °C they qualify as room temperature ILs (RTILs). Their temperature-dependent viscosities and conductivities, together with those of two [Tf(2)N](-) ILs with the same cations and a further siloxane-functionalized [Tf(2)N](-) IL, are measured between 0 and 80 °C, and all are described by the Vogel-Fulcher-Tammann (VFT) equations. We note that the [Al(hfip)(4)](-) ILs have lower viscosities than their [Tf(2)N](-) analogues at all measured temperatures and higher conductivities at room temperature.

The potential use of volatile methylsiloxanes (VMSs) as solvents for chemicals synthesis has been explored.Assessment of the environmental impact of these VMS solvents is made and found to be significantly lower than those of the non-polar organic solvents that they have the potential to replace. The polarities of the VMSs, as expressed by empirical polarity measurements, and miscibilities with other liquids are found to be similar to those of alkane solvents. Finally, some uses of VMSs as solvents for both organic and inorganic transformations are described. The VMSs provide environmentally more sustainable (greener) alternatives to the nonpolar solvents that they have the potential to replace. † Electronic supplementary information (ESI) available. See

Non-flammable electrolytes have been extensively studied to improve the safety of energy storage devices. In this study, a new ionic liquid polymer electrolyte (ILPE) prepared by a cast technique using poly(vinyl chloride) (PVC) as the host polymer was examined for sodium secondary batteries. The ILPE containing 50 wt% of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [C 2 C 1 im][FSA] ionic liquid showed an ionic conductivity of 5.6 mS cm −1 at 318 K. It remains stable up to 517 K based on 5 wt% loss. Stable sodium metal electrodeposition/dissolution was observed at the cathodic limit of the electrochemical window for the ILPE containing Na [FSA] Lithium secondary batteries are used in various applications such as portable electronics, consumer electronics, and auto motives. 1,2However, the uneven distribution of lithium resources might limit their feasibility in large scale energy storage systems. Consequently, sodium secondary batteries have become one of the most promising alternatives to lithium secondary batteries.3 The key advantages of using sodium-based energy storage devices are the low cost, and the abundant resources and low redox potential of sodium (E o Na + /Na = −2.71 vs. SHE; which is ∼0.3 V higher than E o Li + /Li ). While organic electrolytes are currently used in researching sodium secondary batteries, 4,5 ionic liquids (ILs) offer great advantages in terms of safety, such as low vapor pressure, low flammability, high thermal stability, high conductivity, and wide electrochemical window. 6,7 The physical and electrochemical properties of ILs in Na secondary batteries have been studied in recent works. [8][9][10][11][12] In real application, polymerization of the IL is one important technique to retain the advantages of ILs and avoid leakage. As a type of gel polymer electrolytes (GPE), the resulting "ionic liquid polymer electrolytes (ILPEs)" consists of ILs, the host polymer, and another component for electrochemical reactions (e.g alkali metal salt). 13,14 In ILPE, it is assumed that the IL phase is trapped within the polymer matrix, forming a self-standing polymer electrolyte with the ions moving in the liquid phase. The advantages of ILPE are high processability, high flexibility, and high dimensional stability that lead to the elimination of the separator. In comparison with the conventional separator, ILPE offers better capacity to trap liquid electrolytes, 15 and acts as the separator and electrolyte at the same time.One of the most challenging issues for ILPEs is improving the compatibility among the IL, the host polymer, and the third component (e.g. alkali metal salt). Most studies of ILPE for lithium secondary batteries are based this ternary system; using poly(ethylene oxide) (PEO) as a host polymer. [16][17][18][19][20][21] For sodium ion conducting ILPE, only a few candidate host polymers have been demonstrated, including poly(vinylidene difluoride) (PVdF) and poly(vinylidene fluoridehexafluoropropylene) (PVdF-HFP). 22,23 Very recent research also focused on PEO-based I...