The present study analyses the large structural differences, first observed using X-ray diffraction, between 1-alkyl-3-methylimidazolium-based ionic liquids, [C_nmim][Ntf₂] (n = 3, 6, 9), and their counterparts with ether-substituted alkyl side chains, [(C₁OC₁)_(n/3)mim][Ntf₂] (n = 3, 6, 9). The MD simulations—obtained using a non-polarizable atomistic force-field to model the ionic liquids under discussion—demonstrate that the suppression of the nanostructured nature in the ionic liquids with ether chains is persistent along the entire series and it is not due to any modification of the polar network of the ionic liquid but rather due to the different morphologies of the non-polar regions that surround it. The modification of the non-polar regions—shift from bulky segregated domains in [C_nmim][Ntf₂] to thin enveloping ones in [(C₁OC₁)_(n/3)mim][Ntf₂]—are caused by the inability of the oxygen-substituted alkyl side chains to pack effectively side by side, the existence of kinks along the chain that lead eventually to intra-molecular, scorpion-like interactions between the chains and the imidazolium ring, and by their stronger interactions with the cations of the polar network via the lone electron pairs of the ether oxygen atoms.

Herein, seven anions including four imide-based, namely bis[(trifluoromethyl)sulfonyl]imide (TFSI), bis(fluorosulfonyl)imide (FSI), bis[(pentafluoroethyl)sulfonyl]imide (BETI), 2,2,2-trifluoromethylsulfonyl-N-cyanoamide (TFSAM) and 2,2,2-trifluoro-N-(trifluoromethylsulfonyl) acetamide (TSAC), and two sulfonate anions, trifluoromethanesulfonate (triflate, TF) and nonafluorobutanesulfonate (NF), are considered and compared. The volumetric mass density and dynamic viscosity of five ionic liquids containing these anions combined with the commonly used 1-ethyl-3-methylimidazolium cation (C₂C₁im), [C₂C₁im][FSI], [C₂C₁im][BETI], [C₂C₁im][TFSAM], [C₂C₁im][TSAC] and [C₂C₁im][NF] are measured in the temperature range of 293.15 ≤ T/K ≤ 353.15 and at atmospheric pressure. The results show that [C₂mim][FSI] and [C₂mim][TFSAM] exhibit the lowest densities and viscosities among all the studied ionic liquids. The experimental volumetric data is used to validate a more consistent re-parameterization of the CL&P force field for use in MD simulations of ionic liquids containing the ubiquitous bis[(trifluoromethyl)sulfonyl]imide and trifluoromethanesulfonate anions and to extend the application of the model to other molten salts with similar ions.

This work explores the possibility of increasing the ionicity of ionic liquids via the solubilization of inorganic salts in their midst. The resulting purely ionic media—distinct ionic liquid plus inorganic salt mixtures—are liquid in an extensive concentration range and can be aptly denominated High Ionicity Ionic Liquids (HIILs).