Eutectic solvents (ESs) are a relatively new class of solvents that have been arousing a lot of attention due to their easy preparation and great tunability of their thermophysical properties, which has been granting their application in a wide range of areas. The aim of this work is to present a new ES based on the mixture of an organic sodium salt, sodium hexanoate and dodecanoate, and a long alkyl chain carboxylic acid, octanoic, nonanoic, and decanoic acids, and to infer about the effect of introducing a sodium atom. The solid–liquid phase diagrams of these new sodium salt-based ES were determined to evaluate the liquid window where they can be confidently used as solvents. Other important properties of solvents have also been studied, and in particular, density and viscosity, at atmospheric pressure and in the temperature range between 293.15 and 353.15 K, were measured. In addition, the polarity of these new sodium salt-based deep eutectic solvents (DESs) was evaluated in terms of the Kamlet–Taft α, β, and π* and E TN parameters. The obtained results were compared with those of other commonly used hydrophilic and hydrophobic DESs and conclusions were taken.

Novel functionalized ionic liquid (IL) combining an imidazolium‐based cation with branched alkyl chain bearing silyl group, 1‐methyl‐3‐(2‐methyl‐3‐(trimethylsilyl)propyl)imidazolium ([Si−C1−C3‐mim]+), and bis(trifluoromethylsulfonyl)imide ([NTf2]−) anion was synthesized and its thermophysical properties (density, viscosity, surface tension, surface entropy and enthalpy, thermal stability) were studied in a wide temperature range and compared with those of ILs having linear alkyl ([Cn‐mim][NTf2]) and siloxane ([(SiOSi)C1mim][NTf2]) side chains. It was found that at 25 °C [Si−C1−C3‐mim][NTf2] is a liquid with dynamic viscosity of 224 cP (224 mPa s) and density of 1.32 g cm−3. The presence of side branched alkyl chain with trimethylsilyl end‐group prevents crystallization of IL and leads to higher viscosities and lower densities in comparison with commonly known [Cn‐mim][NTf2] (n=2–4). As surface excess enthalpy was found to be in the lower end of the usual range of values for ILs, the interactions between silyl‐functionalized cation and [NTf2] anion can be considered as relatively weak. Finally, [Si−C1−C3‐mim][NTf2] was used for the preparation of polymer supported ionic liquid membranes (SILMs) and their CO2 and N2 permeation properties at 20 °C and 100 kPa were determined: permeability PCO2=311, PN2=12 Barrer, diffusivity DCO2=115×1012, DN2=227×1012 m2 s−1 and CO2/N2 permselectivity αCO2/N2=25.3.

This work aims to explore the gas permeation performance of two newly-designed ionic liquids, [C2mim][CF3BF3] and [C2mim][CF3SO2C(CN)2], in supported ionic liquid membranes (SILM) configuration, as another effort to provide an overall insight on the gas permeation performance of functionalized-ionic liquids with the [C2mim]+ cation. [C2mim][CF3BF3] and [C2mim][CF3SO2C(CN)2] single gas separation performance towards CO2, N2, and CH4 at T = 293 K and T = 308 K were measured using the time-lag method. Assessing the CO2 permeation results, [C2mim][CF3BF3] showed an undermined value of 710 Barrer at 293.15 K and 1 bar of feed pressure when compared to [C2mim][BF4], whereas for the [C2mim][CF3SO2C(CN)2] IL an unexpected CO2 permeability of 1095 Barrer was attained at the same experimental conditions, overcoming the results for the remaining ILs used for comparison. The prepared membranes exhibited diverse permselectivities, varying from 16.9 to 22.2 for CO2/CH4 and 37.0 to 44.4 for CO2/N2 gas pairs. The thermophysical properties of the [C2mim][CF3BF3] and [C2mim][CF3SO2C(CN)2] ILs were also determined in the range of T = 293.15 K up to T = 353.15 K at atmospheric pressure and compared with those for other ILs with the same cation and anion’s with similar chemical moieties.