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Raman spectra in the range of the totally symmetric stretching mode of the [PF6]- anion, νs(PF6), have been measured for 1-alkyl-3-methylimidazolium ionic liquids [CnC1im][PF6], for n = 4, 6, and 8, as a function of pressure at room temperature. The ionic liquids [C6C1im][PF6] and [C8C1im][PF6] remain in an amorphous phase up to 3.5 GPa, in contrast to [C4C1im][PF6], which crystallizes above ∼0.5 GPa. Equations of state based either on a group contribution model or Carnahan-Starling-van der Waals model have been used to estimate the densities of the ionic liquids at high pressures. The shifts of the vibrational frequency of νs(PF6) with density observed in [C6C1im][PF6] and in [C8C1im][PF6] have been calculated by a hard-sphere model of a pseudo-diatomic solute under short-range repulsive interactions with the neighboring particles. The stochastic model of Kubo for vibrational dephasing has been used to obtain the amplitude of vibrational frequency fluctuation, <Δω2>, and the relaxation time of frequency fluctuation, τc, as a function of density by Raman band shape analysis of the νs(PF6) mode of [C6C1im][PF6] and [C8C1im][PF6]. [ABSTRACT FROM AUTHOR]

Carbon dioxide absorption by mixtures of two ionic liquids with a common cation―1-butyl-3-methylimidazolium acetate, [C4C1Im][OAc], and 1-butyl-3-methylimidazolium tricyanomethanide, [C4C1Im][C(CN)3]―was determined experimentally at pressures below atmospheric pressure as a function of temperature between 303 K and 343 K, and at 303 K as a function of pressure up to 10 bar. It is observed that the absorption of carbon dioxide decreases with increasing tricyanomethanide anion concentration and with increasing temperature, showing a maximum of 0.4 mole fraction of carbon dioxide in pure [C4C1Im][OAc] at 303 K. At this temperature, the CO2 absorption in the mixtures [C4C1Im][OAc](1−x)[C(CN)3]x is approximately the mole-fraction average of that in the pure ionic liquids. By applying an appropriate thermodynamic treatment, after identification of the species in solution, it was possible to calculate both the equilibrium constant, Keq, and Henry's law constant, KH, in the different mixtures studied thus obtaining an insight into the relative contribution of chemical and physical absorption of the gas. It is shown that chemical sorption proceeds through a 1 : 2 stoichiometry between CO2 and acetate-based ionic liquid. The presence of the C(CN)3− anion does not significantly affect the chemical reaction of the gas with the solvent (Keq = 75 ± 2 at 303 K) but leads to lower Henry's law constants (from KH = 77.8 ± 0.6 bar to KH = 49.5 ± 0.5 bar at 303 K), thus pointing towards larger physical absorption of the gas. The tricyanomethanide anion considerably improves the mass transfer by increasing the fluidity of the absorbent as proven by the larger diffusivities of all the ions when the concentration of the C(CN)3− anion increases in the mixtures. [ABSTRACT FROM AUTHOR]

Carbon dioxide absorption by mixtures of two ionic liquids with a common cation-1-butyl-3-methylimidazolium acetate, [C 4 C 1 Im][OAc], and 1-butyl-3-methylimidazolium tricyanomethanide, [C 4 C 1 Im][C(CN) 3 ]-was determined experimentally at pressures below atmospheric pressure as a function of temperature between 303 K and 343 K, and at 303 K as a function of pressure up to 10 bar. It is observed that the absorption of carbon dioxide decreases with increasing tricyanomethanide anion concentration and with increasing temperature, showing a maximum of 0.4 mole fraction of carbon dioxide in pure [C 4 C 1 Im][OAc] at 303 K. At this temperature, the CO 2 absorption in the mixtures [C 4 C 1 Im][OAc] (1-x) [C(CN) 3 ] x is approximately the mole-fraction average of that in the pure ionic liquids. By applying an appropriate thermodynamic treatment, after identification of the species in solution, it was possible to calculate both the equilibrium constant, K eq , and Henry's law constant, K H , in the different mixtures studied thus obtaining an insight into the relative contribution of chemical and physical absorption of the gas. It is shown that chemical sorption proceeds through a 1 : 2 stoichiometry between CO 2 and acetate-based ionic liquid. The presence of the C(CN) 3 - anion does not significantly affect the chemical reaction of the gas with the solvent (K eq = 75 ± 2 at 303 K) but leads to lower Henry's law constants (from K H = 77.8 ± 0.6 bar to K H = 49.5 ± 0.5 bar at 303 K), thus pointing towards larger physical absorption of the gas. The tricyanomethanide anion considerably improves the mass transfer by increasing the fluidity of the absorbent as proven by the larger diffusivities of all the ions when the concentration of the C(CN) 3 - anion increases in the mixtures.

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 (T(d)) measured by thermogravimetric analysis, and by their melting point (T(m)), glass transition (T(g)) and crystallization temperatures (T(cryst)) 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 298.15K. 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)°, 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., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The solubility of halogen gases--fluorine, chlorine and bromine--has been determined experimentally in several fluorinated solvents between 283 and 323 K at atmospheric pressure. The solubility of chlorine was studied in perfluorooctane, perfluorohexane, perfluorohexylethane, perfluoromethylcyclohexane, perfluoro-1,3-dimethylcyclohexane, perfluoro-2-butyltetrahydrofuran, and perfluoroperhydrophenanthrene and was found to be on the order of 10(-2) in mole fraction. The solubility of fluorine in the studied fluorinated solvents at 298 K is 1 order of magnitude lower than the solubility of chlorine. The solubility of bromine was studied as a function of temperature in perfluorooctane, and it was found to be higher than that of chlorine but of the same order of magnitude. The experimental studies were complemented by molecular simulation calculations. The molecular force fields used for the halogen gases and for the fluorinated solvents were taken, when possible, from the literature. An intermolecular potential model had to be developed for perfluoro-2-butyltetrahydrofuran, with a functional form of the Lennard-Jones plus point charges type. The solubility of the three gases was calculated by molecular simulation using Widom test-particle insertion. Dissimilar interaction parameters of 0.89 and 0.75 in the Lennard-Jones well depths between the solute and the solvent had to be introduced to reach agreement with the experimental results for chlorine and fluorine solubilities, respectively. The structure of the solutions was studied by analysis of solute-solvent radial distribution functions. It was found that the preferential solvation sites for the halogen gases are the terminal CF3 groups of the different fluorinated solvents.

New data on the aqueous solubility of n-octane, 1-chlorooctane and 1-bromooctane are reported between 1 degree C and 45 degrees C. Henry's law constants, K(H), and air/water partition coefficients, K(AW), were calculated by associating the measured solubility values to vapor pressures taken from literature. The mole fraction aqueous solubility varies between (1.13-1.60)x10(-7) for n-octane with a minimum at approximately 23 degrees C, (3.99-5.07)x10(-7) for 1-chlorooctane increasing monotonically with temperature and (1.60-3.44)x10(-7) for 1-bromooctane with a minimum near 18 degrees C. The calculated air-water partition coefficients increase with temperature and are two orders of magnitude lower for the halogenated derivatives compared to octane. The precision of the results, taken as the average absolute deviations of the aqueous solubility, the Henry's law constants, or the air/water partition coefficients, from appropriate smoothing equations as a function of temperature is of 3% for n-octane and of 2% and 4% for 1-chlorooctane and 1-bromooctane, respectively. A new apparatus based on the dynamic saturation column method was used for the solubility measurements. Test measurements with n-octane indicated the capability of measuring solubilities between 10(-6) and 10(-10) in mole fraction, with an estimated accuracy better than +/-10%. A thorough thermodynamic analysis of converting measured data to air/water partition coefficients is presented.