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The density, heat capacity and viscosity of two magnetic ionic liquids sharing the same Fe (III)-containing anion, specifically, [C4mim][FeCl4] and [P6 6 6 14][FeCl4], have been determined, along with their volumetric expansivity, and thermal decomposition temperatures. The magnetic properties of the two compounds have been studied using SQUID magnetometry. Both [C4mim][FeCl4] and [P6 6 6 14][FeCl4] are paramagnetic, but while in the first case the magnetic moment value is 5.8 μB/Fe, therefore close to that of Fe3+, for the latter it is only 4.8 μB/Fe. The effective concentration of magnetic sites is almost three times greater for [C4mim][FeCl4] as compared to [P6 6 6 14][FeCl4]. In this latter case, the experimental isothermal magnetization curves do not follow a Brillouin-type of behavior; alternatively, the results were discussed using the Spin Hamiltonian formalism in terms of both the distortion of the Iron site and covalence effects.

Three pyrrolidinium-based ionic liquids—N-dodecyl-N-methylpyrrolidinium bromide, N-butyl-N-octylpyrrolidinium bromide, and N-butyl-N-dodecylpyrrolodinium bromide—were synthesized and characterized by their decomposition temperatures (Td) measured by thermogravimetric analysis, and by their melting point (Tm), glass transition (Tg) and crystallization temperatures (Tcryst) determined by differential scanning calorimetry. Their self-aggregation properties in aqueous solution were studied and their behavior is compared with that of analogous conventional cationic surfactants, namely tetra-alkylammonium bromide salts. The critical micellar concentration, cmcs were obtained by isothermal titration calorimetry (ITC); which were further validated by measurements of interfacial tension, fluorescence and NMR spectroscopy. Enthalpies of micellization were measured at three different temperatures using ITC. The Taylor dispersion method and DOSY NMR were used to determine diffusion coefficients of the ionic liquid surfactants in aqueous solution at 298.15 K. Several correlations between structural features of the surfactant species, such as the number and size of their alkyl chains, and the thermodynamic quantities of micellization—expressed by experimental values of cmc, counter-ion binding fraction, Δ mic G ∘ , Δ mic H ∘ , and Δ mic S ∘ —are established. We could interpret the different contributions of the two alkyl side chains to the aggregation properties in terms of the balance of interactions in homogeneous and micellar phases, contributing to understanding the aggregation behavior of ionic liquids in water and the parallel between these systems and traditional ionic surfactants.

A study comprising the adsorption and frictional behaviour of 1-alkyl-3-methylimidazolium chloride ionic liquids, [C n mim][Cl] (with n = 10,12,14), deposited on gold surfaces at a fixed concentration of 0.07 M was carried out using a quartz crystal microbalance (QCM), a nanotribometer and an atomic-force microscope (AFM). The size of the alkyl side-chain of the cation and the corresponding adsorption and frictional results correlate quite well. AFM morphological images support the reasoning put forward for the observed trends. They also suggest that the alkyl chain length of the cation plays an important role in the definition of the structure of the adsorbed aggregates. The ratio between the working concentrations and the critical micelle concentration of the studied ionic liquids is also an important factor.

The high degree of organisation in the fluid phase of room-temperature ionic liquids has major consequences on their macroscopic properties, namely on their behaviour as solvents. This nanoscale self-organisation is the result of an interplay between two types of interaction in the liquid phase – Coulomb and van der Waals – that eventually leads to the formation of medium-range structures and the recognition of some ionic liquids as composed of a high-charge density, cohesive network permeated by low-charge density regions.

The interactions between ionic liquids and totally fluorinated alkanes are investigated by associating gas solubility measurements with molecular simulation calculations. Experimental values for the solubility of perfluoromethane, perfluoroethane, and perfluoropropane in one ionic liquidtrihexyltetradecylphophonium bis(trifluoromethylsulfonyl)amide [P 6,6,6,14][Ntf 2]are reported between 303 and 343 K and close to atmospheric pressure. All mole fraction solubilities decrease with increasing temperature. From the variation of Henry's law constants with temperature, the thermodynamic functions of solvation were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations, is always better than +/-3%. By the analysis of the differences between the solute-solvent radial distribution functions of perfluoromethane and perfluoropropane obtained by molecular simulation, it was possible to explain why solubility increases with the size of the perfluoroalkane. The trend of solubility is explained on the basis of the location of the solute with respect to the solvent ions as well as on the differences in the solute-solvent energies of interaction.