Using FT-IR Spectroscopy to Measure Charge Organization in Ionic Liquids

A major goal in the field of ionic liquids is correlating transport property trends with the underlying liquid structure of the compounds, such as the degree of charge organization among the constituent ions. Traditional techniques for experimentally assessing charge organization are specialized and not readily available for routine measurements. This represents a significant roadblock in elucidating these correlations. We use a combination of transmission and polarized-ATR infrared spectroscopy to measure the degree of charge organization for ionic liquids. The technique is illustrated with a family of 1-alkyl-3-methylimidazolium trifluoromethanesulfonate ionic liquids at 30 °C. As expected, the amount of charge organization decreases as the alkyl side chain is lengthened, highlighting the important role of short-range repulsive interactions in defining quasilattice structure. Inherent limitations of the method are identified and discussed. The quantitative measurements of charge organization are then correlated with trends in the transport properties of the compounds to highlight the relationship between charge and momentum transport and the underlying liquid structure. Most research laboratories possess infrared spectrometers capable of conducting these measurements; thus, the proposed method may represent a cost-effective solution for routinely measuring charge organization in ionic liquids

Nanoconfinement-Induced Phase Segregation of Binary Benzene–Cyclohexane Solutions within a Chemically Inert Matrix

Binary solutions provide a fertile arena to probe intermolecular and molecular/surface interactions under nanoconfinement. Here, the phase segregation of a solution comprising 0.80 mol fraction benzene and 0.20 mol fraction cyclohexane confined within SiO₂ nanopores was evaluated using small-angle neutron scattering with hydrogen–deuterium contrast matching. It is demonstrated that benzene and cyclohexane are fully miscible at 303 K (30 °C), yet they unambiguously phase segregate by 153 K (−120 °C), which is below their respective freezing points and below the cubic-to-monoclinic phase transition of cyclohexane. Specifically, the cyclohexane and benzene separate into a core|shell morphology with cyclohexane concentrated toward the nanopore centers. Additionally, pure benzene is shown to form a frozen core of bulk density with a thin shell of slightly reduced density immediately adjacent to the SiO₂ nanopore wall at 153 K. Because the SiO₂ matrix is chemically inert to cyclohexane and benzene, the observed radially dependent phase segregation is strong evidence for the effects of confinement alone, with minimal host–wall attraction