High-pressure speed of sound and related thermodynamic properties of N-alkylpyridinium bis(trifluoromethylsulfonyl)imides

The speed of sound was measured in three N-alkylpyridinium bis(trifluoro-methylsulfonyl)imides containing cations with ethyl, butyl and hexyl chains at pressures up to 101 MPa over a temperature range from 293.15 to 323.15 K. This paper is the first reported direct measurement of the speed of sound in N-hexylpyridinium bis (trifluoro-methylsulfonyl)imide as a function of pressure and temperature at two frequencies (1.95 and 6.25 MHz), demonstrating the absence of ultrasonic velocity dispersion under experimental conditions. An acoustic method was used to determine the high-pressure density, isentropic compressibility, isothermal compressibility, isobaric thermal expansion, isobaric and isochoric heat capacities, and internal pressure. For the studied homologous series, the dependence of the speed of sound on the alkyl chain length of the pyridinium cation exhibits a minimum at both atmospheric and high pressures. With increasing pressure, the minimum becomes shallower and is shifted towards homologues with shorter carbon chains in the cation

Acoustic nonlinearity parameter B/A, internal pressure, and acoustic impedance determined at pressures up to 100 MPa for 1-Ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide

The nonlinearity parameter B/A, internal pressure, and acoustic impedance are calculated for a room temperature ionic liquid, i.e. for 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide for tem- peratures from (288.15 to 318.15) K and pressures up to 100 MPa. The B/A calculations are made by means of a thermodynamic method. The decrease of B/A values with the increasing pressure is observed. At the same time B/A is temperature independent in the range studied. The results are compared with corresponding data for organic molecular liquids. The isotherms of internal pressure cross at pressure in the vicinity of 70 MPa, i.e. in this range the internal pressure is temperature independent

Isobaric and Isochoric Heat Capacities of Imidazolium-Based and Pyrrolidinium-Based Ionic Liquids as Function of Temperature: Modeling of Isobaric Heat Capacity

International audienceThe isobaric and isochoric heat capacities of seven 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, two 1-alkyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imides, and two bis(1-alkyl-3-methylimidazolium) tetrathiocyanatocobaltates were determined at atmospheric pressure in the temperature range from 293.15 to 323.15 K. The isobaric heat capacities were determined by means of differential scanning calorimetry, whereas isochoric heat capacities were determined along with isothermal compressibilities indirectly by means of the acoustic method from the speed of sound and density measurements. Based on the experimental data, as expected, the isobaric heat capacity increases linearly with increasing alkyl chain length in the cation of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides and no odd and even carbon number effect is observed. After critical comparison of the obtained data with the available literature data, the most reliable values are recommended. It has been also shown that, although the COSMOthermX calculations underestimated the isobaric heat capacity values whatever the temperature and the ionic liquid structure, the approach used during this work may be applied to estimate physical properties of non-single-charged ions as well. Additionally, based on the speeds of sound the thermal conductivities were calculated using a modified Bridgman relation

Speed of Sound and Ultrasound Absorption in Ionic Liquids

International audienceA complete review of the literature data on the speed of sound and ultrasound absorption in pure ionic liquids (ILs) is presented. Apart of the analysis of data published to date, the significance of the speed of sound in ILs is regarded. An analysis of experimental methods described in the literature to determine the speed of sound in ILs as a function of temperature and pressure is reported, and the relevance of ultrasound absorption in acoustic investigations is discussed. Careful attention was paid to highlight possible artifacts, and side phenomena related to the absorption and relaxation present in such measurements. Then, an overview of existing data is depicted to describe the temperature and pressure dependences on the speed of sound in ILs, as well as the impact of impurities in ILs on this property. A relation between ions structure and speeds of sound is presented by highlighting existing correlation and evaluative methods described in the literature. Importantly, a critical analysis of speeds of sound in ILs vs those in classical molecular solvents is presented to compare these two classes of compounds. The last part presents the importance of acoustic investigations for chemical engineering design and possible industrial applications of ILs

Cytotoxicity of ionic liquids on normal human dermal fibroblasts in the context of their present and future applications

The skin is the part of the body that is the most exposed to toxic substances; therefore, the impact of chemicals on the skin should be thoroughly studied prior to their implementation in any industrial-scale application. Herein, we examined and analyzed the influence of the structure of both the cation and anion of 31 different ionic liquids (ILs) on their cytotoxicity against normal human dermal fibroblasts in the context of their present and future potential applications. We found that imidazolium-based ILs combined with dialkyl phosphate anions or with the ethyl sulfate anion are the least cytotoxic. Notably, 1,3-diethylimidazolium ethyl sulfate can be potentially used as a hydraulic fluid similar to the commercially available hydraulic medium based on 1-ethyl-3-methylimidazolium ethyl sulfate. Moreover, the dialkyl phosphate-based ILs are considered as an efficient solvent for the utilization of lignocellulose-based biomass and as an extractant in eco-friendly and cost-effective processes for the extraction of bioplastic. Pyrrolidinium-based and cyano-based ILs, often used as heat transfer media and base fluids for ionanofluids, were also identified herein as good candidates based on their relatively low toxicity compared to other ILs

Comparative study of effect of alkyl chain length on thermophysical characteristics of five N-alkylpyridinium bis(trifluoromethylsulfonyl)imides with selected imidazolium-based ionic liquids

International audienceThe series of N-alkylpyridiniumbis(trifluoromethylsulfonyl)imide, [Cnpy][NTf2],where n=2, 3, 4, 6, and 8 havebeen synthesized and the effect of alkyl chain length in cation on their thermophysical properties have been studiedand compared with those observed in analogous imidazolium-based ILs. To drive this comparison, the speedof sound, density, isobaric heat capacity, electric conductivity, TGA for all [Cnpy][NTf2], aswell as, refractive indexof [Cnpy][NTf2] (n = 3, 6) and surface tension of [Cnpy][NTf2] (n = 2, 4, 6, 8) were determined as a function oftemperature at atmospheric pressure. From these experimental data, the isentropic compressibility, isobaricthermal expansion, isothermal compressibility, isochoric heat capacity, internal pressure, as well as, the surfaceentropy and surface enthalpy were calculated. The electric conductivity together with the literature viscositydata are used to obtain the Walden plot for the investigated ionic liquids. The minimum of the speed of sounddependence on the alkyl chain length in the cation is observed for [C6py][NTf2]. The isentropic compressibilityand the isothermal compressibility of [Cnpy][NTf2] increase with increasing alkyl chain length in the cation andthe slope of this dependence is changed around n = 6. These effects were more pronounced than that forimidazolium-based ionic liquids with [NTf2]− anion. Finally, COSMOthermX software was used to further evaluateits predictive capability by comparing calculated density and isobaric heat capacity as a function of the ILstructure and temperature with experimental data for the [Cnpy][NTf2] (n = 2, 3, 4, 6, 8) series. This analysisshows a very good agreement in the case of the Cp with an average absolute relative deviation close to 1.4%while a deviation close to 0.72% is observed in the case of the density of the [Cnpy][NTf2]

An Ultrasonic Relaxation Study of 1-Alkyl-3-Methylmidazolium-Based Room Temperature Ionic Liquids: Probing the Role of Alkyl Chain Length in the Cation

Ultrasound absorption spectra of four 1-alkyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imides were determined as a function of the alkyl chain length on the cation from 1-propyl to 1-hexyl from 293.15 to 323.15 K at ambient pressure. Herein, the ultrasound absorption measurements were carried out using a standard pulse technique within a frequency range from 10 to 300 MHz. Additionally, the speed of sound, density, and viscosity have been measured. The presence of strong dissipative processes during the ultrasound wave propagation was found experimentally, i.e., relaxation processes in the megahertz range were observed for all compounds over the whole temperature range. The relaxation spectra (both relaxation amplitude and relaxation frequency) were shown to be dependent on the alkyl side chain length of the 1-alkyl-3-methylimidazolium ring. In most cases, a single-Debye model described the absorption spectra very well. However, a comparison of the determined spectra with the spectra of a few other imidazolium-based ionic liquids reported in the literature (in part recalculated in this work) shows that the complexity of the spectra increases rapidly with the elongation of the alkyl chain length on the cation. This complexity indicates that both the volume viscosity and the shear viscosity are involved in relaxation processes even in relatively low frequency ranges. As a consequence, the sound velocity dispersion is present at relatively low megahertz frequencies