Jerzy Szydłowski

A detailed thermodynamic analysis of [C4mim][BF4]+ water as a case study to model ionic liquid aqueous solutions

Since determining experimentally a wide variety of thermophysical properties—even for a very small portion of the already known room temperature ionic liquids (and their mixtures and solutions)—is an impossible goal, it is imperative that reliable predictive methods be developed. In turn, these methods might offer us clues to understanding the underlying ion–ion and ion–molecule interactions. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of the most thoroughly investigated ionic liquids, together with water, the greenest of the solvents, have been chosen in this work in order to use their mixtures as a case study to model other, greener, ionic liquid aqueous solutions. We focus our attention both on very simple methodologies that permit one to calculate accurately the mixtures molar volumes and heat capacities as well as more sophisticated theories to predict excess properties, pressure and isotope effects in the phase diagrams, and anomalies in some response functions to criticality, with a minimum of information. In regard to experimental work, we have determined: (a) densities as a function of temperature (278.15 < T/K < 333.15), pressure (1 < p/bar < 600), and composition (0 < xIL < 1), thus also excess molar volumes; (b) heat capacities and excess molar enthalpies as a function of temperature (278.15 < T/K < 333.15) and composition (0 < xIL < 1); and (c) liquid–liquid phase diagrams and their pressure (1 < p/bar < 700) and isotopic (H2O/D2O) dependences. The evolution of some of the aforementioned properties in their approach to the critical region has deserved particular attention.

Changing from an unusual high-temperature demixing to a UCST-type in mixtures of 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide and arenes

Upper critical solution temperature (UCST) combined with a high-temperature demixing type of phase diagrams are reported for binary liquid mixtures containing the ionic liquids, 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide ([Cnmim][NTf2], where n = 2, 4, 6, 8, 10) and benzene, toluene, or α-methylstyrene (PhC(Me)CH2), at atmospheric and moderately high pressure. The phase diagrams were determined either using a dynamic method with visual detection of phase transitions or a laser light scattering technique. In our investigations, as the imidazolium alkyl chain length of the ionic liquid increases, the mixtures containing an arene evolve from a rarely found high-temperature demixing behaviour, to “hour-glass”, to the common phase splitting as temperature diminishes (UCST, whenever a critical point was found). For the three systems containing specifically [C10mim][NTf2] with benzene, toluene, or α-methylstyrene, data were also collected up to 5 MPa using a high-pressure laser light scattering apparatus. For all phase diagrams, the critical compositions correspond to low concentrations of the ionic liquid. This fact underlies the possibility that ionic liquids, even in relatively dilute solutions, tend to form multiple-ion aggregates. This was corroborated by electro-spray mass spectrometry.

Miscibility of Ionic Liquids with Polyhydric Alcohols

Liquid-liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by ionic liquids ([bmim][BF(4)], [bmim][PF(6)], [emim][Tf(2)N], [bmim][Tf(2)N], [hmim][Tf(2)N]) and polyhydric alcohols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, 1,2-butanediol). The impact of ionic liquid and di- or three-hydroxy alcohol characteristics focusing on the effect of the ILs anion nature, cation alkyl chain length, and alcohol structure (number of hydroxyl groups, position of the hydroxy groups in the molecule, and number of carbon atoms in the diols) is presented. It appears that all systems exhibit upper critical solution temperatures. For dihydroxy alcohols mentioned above, miscibility with 1-butyl-3-methylimidazolium ionic liquids follows the order [BF(4)](-) > [Tf(2)N](-) > [PF(6)](-) and is dependent on the hydrogen-bond basicity of the anion. Analysis of these findings leads us to conclude that the miscibility of ionic liquids is likely related to the hydrogen-bond acceptor strength of the anion. Comparing the miscibility of 1,2-ethanediol with 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, it can be seen that surprisingly, T(c)([emim](+)) < T(c)([bmim](+)) < T(c)([hmim](+)). This arrangement of critical temperatures is opposite to that observed earlier for systems with monohydroxy alcohols. Analyzing the influence of the polyhydroxy alcohol structure, we also noticed that the miscibility of the polyhydroxy alcohols with [bmim][Tf(2)N] or [bmim][BF(4)] decreases when the polarity of the alcohol rises.

Isotope effect on miscibility of acetonitrile and water

Abstract The miscibility of four binary liquid mixtures containing acetonitrile (ACN, ACN-d3) and water (H2O, D2O) has been studied. All the measured systems present solubility curves characterized by slight asymmetry and the presence of an upper critical solution temperature (UCST). It is found that all systems have approximately the same critical composition and approximately the same shape of the phase diagrams. There is also no influence on the critical exponent. However, it has been found that isotope substitution diminishes solubility in each case independently of the site of deuterium substitution. This observation is accounted for in terms of the specific interactions of acetonitrile and water.

Excess enthalpies of mixing, effect of temperature and composition on the density, and viscosity and thermodynamic properties of binary systems of {ammonium-based ionic liquid + alkanediol}.

In the present work the excess enthalpies of butyltrimethylammonium bis(trifluoromethyl-sulfonyl)imide, [N1114][NTf2], with 1,2-propanediol, or 1,2-butanediol, or 2,3-butanediol have been measured at T = 298.15 K. Additionally, the density, ρ, and dynamic viscosity, η, for binary solutions containing ionic liquids (ILs) and alkanedioles, {butyltrimethylammonium bis(trifluoromethyl-sulfonyl)imide, [N1114][NTf2], + 1,2-propanediol, 1,2-butanediol, 2,3-butanediol} and {(2-hydroxyethyl)trimethylammonium bis(trifluoro-methylsulfonyl)imide, [N1112OH][NTf2], + 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol}, at wide temperature and composition ranges at ambient pressure have been investigated. From experimental values of the density, ρ, and dynamic viscosity, η, the excess molar volumes, V(E), and dynamic viscosity deviations, Δη, were calculated and correlated using the Redlich-Kister polynomial equation. The temperature dependence of density and viscosity for the tested binary systems was described by an empirical second-order polynomial and by the Vogel-Fucher-Tammann equation, respectively. The variation of density and viscosity as a function of composition has been described by the polynomial correlations. Comparison of the experimental results for the binary mixtures tested in this work allows us to determine the influence of alkanediol carbon chain length, the position of the hydroxyl group in the alcohol, and the influence of the structure of the cation of the ionic liquid on the presented properties.

Thermodynamic Study of Binary Mixtures of 1-Butyl-1-methylpyrrolidinium Dicyanamide Ionic Liquid with Molecular Solvents: New Experimental Data and Modeling with PC-SAFT Equation of State

This work is concerned with thermodynamic properties of binary mixtures composed of 1-butyl-1-methylpyrrolidinium dicyanamide ionic liquid (IL) and the following molecular solvents: n-heptane, benzene, toluene, ethylbenzene, thiophene, 1-butanol, 1-hexanol, and 1-octanol. This is the very first time when experimental data on liquid-liquid equilibrium (LLE) phase diagrams and excess enthalpies of mixing (H(E)) for these systems are reported. An impact of the molecular solvent structure on LLE and H(E) is discussed. Furthermore, modeling of the properties under study is presented by using perturbed-chain statistical associating fluid theory (PC-SAFT). The equation of state is used in purely predictive and semipredictive mode. The latter one involves temperature-dependent binary corrections to combining rules employed in the PC-SAFT model determined on the basis of infinite dilution activity coefficients. The results shown indicate that such an approach can serve as an interesting modern thermodynamic tool for representation of thermodynamic data for complex ILs-based systems.

Solvent H/D isotope effects on miscibility and Θ-temperature in the polystyrene–cyclohexane system

High-accuracy cloud-point temperatures for polystyrene–cyclohexane (PS–CH) and polystryrene–deuterated cyclohexane (PS–CH-d) solutions were measured over a broad range of molecular weights: 2.5 × 104 ≤ Mw ≤ 1.32 × 107. All polystyrene samples were characterized by low polydispersity indexes. Deuterium substitution in cyclohexane shifts the UCSTs to higher values and this isotope shift increases with increasing molecular weight, reaching at the limit of infinite Mw the value 4.53 K. No isotope effect on the critical concentration has been detected. Using different methods, Θ-temperatures for both PS–CH and PS–CH-d systems were determined. All approaches generate consistent results and a remarkable isotope effect on the Θ-temperature is observed. It is shown that isotopic shifts on UCST and Θ-temperature translate as a red shift of the C–H stretching frequency of cyclohexane on its transfer from a pure liquid to polymer solution at infinite dilution. The effect of pressure on the Θ-temperature has also been analyzed and it appears to mimic that of the pressure dependence of the critical temperatures of polystyrene–cyclohexane solution. It is also shown that the frequency shift of C–H vibrations changes with pressure in a similar fashion.

Isotope effects on phase equilibria in hydrogen bonded systems, especially vapor pressure and miscibility isotope effects

Abstract Vapor pressure and miscibility isotope effects in hydrogen bonded systems are reviewed. It is shown that the changes caused by H/D substitution reflect the molecular structure. Condensed phase isotope effects are therefore suggested to be a valuable tool for the investigation of intermolecular interactions in liquids and solutions.

Deuterium isotope effect on miscibility of some binary mixtures containing acetonitrile or nitromethane

Abstract The liquid–liquid miscibility temperatures as a function of composition and deuterium substitution have been determined experimentally for the binary systems formed by acetonitrile or nitromethane with decanol and tetrachloroethylene including their deuterated forms. The following deuterated compounds were used: acetonitrile-d 3 , nitromethane-d 3 and decanol-d 1 . It appears that deuteration of the methyl group in acetonitrile or nitromethane leads to the significant upward shift of the upper critical solution temperature. This effect is discussed on the basis of the intermolecular interaction emphasizing the role of the strong dipole–dipole interaction between acetonitrile (or nitromethane) molecules. Deuterium substitution in OH group of decanol generates a weak downward shift of the upper critical solution temperature. It is believed that in this particular case the better miscibility upon deuterium substitution results from hydrophobic action of the large alkyl group obscuring the OH(D) group and restricting hydrogen bonding formation with this group.

NH2/ND2-vapour pressure isotope effect of cyclopropylamine

The NH2/ND2-vapour pressure isotope effect has been determined between 283 and 333 K for cyclopropylamine, an amine with a strong ring strain. The measurements are represented by the relation ln[P(C3H5N2H2)/P(C3H5NH2)] = −(8821.73 ± 68.949) (K/T)2 + (23.379 ± 0.223)K/T and correspond to a normal (PD/PH < 1) effect. They suggest an association that is slightly weaker than that of propylamine and nearly agrees with that of isopropylamine. The differences are discussed in terms of acidities and steric factors.