-
[show abstract]
[hide abstract]
ABSTRACT: The liquid-liquid equilibria of mixtures of cholinum-based ionic liquids (N-alkyl-N,N-dimethylhydroxyethylammonium bis(trifluoromethane)sulfonylimide, [N(11n2OH)][Ntf(2)], n = 1, 2, 3, 4, and 5) plus water or 1-octanol were investigated at atmospheric pressure over the entire composition range. The experiments were conducted between 265 and 385 K using the cloud-point method. The systems exhibit phase diagrams consistent with the existence of upper critical solution temperatures. The solubility of [N(1 1 n 2OH)][Ntf(2)] in water is lower for cations with longer alkyl side chains (larger n values). The corresponding trend in the octanol mixtures is reversed. The ([N(1 1 1 2OH)][Ntf(2)] + water + octanol) ternary system shows triple liquid-liquid immiscibility at room temperature and atmospheric pressure. A combined analytic/synthetic method was used to estimate the corresponding phase diagram under those conditions. Auxiliary molecular dynamics simulation data were used to interpret the experimental results at a molecular level.
The Journal of Physical Chemistry B 07/2012; 116(30):9186-95. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Density and viscosity data of the N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ionic liquids homologous series [N(1 1 n 2(OH))][Ntf(2)] with n=1, 2, 3, 4 and 5 have been measured at atmospheric pressure in the 283<T/K<373 temperature range and the corresponding isobaric thermal expansion coefficients have been calculated. This work studies the effect of increasing the alkyl chain length of the cholinium-based cation on the density, viscosity and related properties of this family of ionic liquids. A volumetric predictive method based on the effective molar volume of cations and anions is used to estimate the effective molar volume of the different cations present in this study. The results agree with data for other cation families that show a molar volume increment per CH(2) group on the alkyl chain of the cation of about 17.2 cm(3) mol(-1), except for [N(1 1 1 2(OH))](+), which exhibits an outlier behaviour. Molecular dynamics simulation results are used to explain the volumetric behaviour along the homologous series from a molecular perspective. The predictive power of group contribution methods for density and viscosity is also tested.
ChemPhysChem 02/2012; 13(7):1902-9. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Molecular dynamics simulations of a 5 nm-thick layer of the ionic liquid 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, [(OH)C2C1im][BF4], over silica, alumina and boro-silicate glass substrates have been performed. The structure of the ionic liquid at the solid-liquid interface has been interpreted taking into account the corresponding normal density profiles, lateral interfacial structure, orientational ordering and planar density contours. Comparisons with experimental data suggest that the adsorption and stratification process of ionic liquids over solid substrates can be correctly modeled using a realistic rendition of a non-uniform amorphous substrate such as a glass material.
Faraday Discussions 01/2012; 154:155-69; discussion 189-220, 465-71. · 5.00 Impact Factor
-
Marisa A. A. Rocha,
Carlos F. R. A. C. Lima,
Lígia R. Gomes,
Bernd Schröder,
João A. P. Coutinho,
Isabel M. Marrucho,
José M. S. S. Esperança,
Luís P. N. Rebelo, Karina Shimizu,
José N. Canongia Lopes,
Luís M. N. B. F. Santos
[show abstract]
[hide abstract]
ABSTRACT: For the first time, two distinct trends are clearly evidenced for the enthalpies and entropies of vaporization along the [Cnmim][Ntf2] ILs series. The trend shifts observed for ΔlgHmo and ΔlgSmo, which occur at [C6mim][Ntf2], are related to structural modifications. The thermodynamic results reported in the present article constitute the first quantitative experimental evidence of the structural percolation phenomenon and make a significant contribution to better understanding of the relationship among cohesive energies, volatilities, and liquid structures of ionic liquids. A new Knudsen effusion apparatus, combined with a quartz crystal microbalance, was used for the high-accuracy volatility study of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series ([Cnmim][Ntf2], where n = 2, 3, 4, 5, 6, 7, 8, 10, 12). Vapor pressures in the (450–500) K temperature range were measured, and the molar standard enthalpies, entropies, and Gibbs energies of vaporization were derived. The thermodynamic parameters of vaporization were reported, along with molecular dynamic simulations of the liquid phase structure, allowing the establishment of a link between the thermodynamic properties and the percolation phenomenon in ILs.
J. Phys. Chem. B. 08/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: INTRODUCTION Thin liquid wetting films have been under investigation during the past decades because of their importance from both practical and theoretical points of view. 1,2 A number of authors have studied films of aqueous solutions of electrolytes and surfactants with the objective of understanding the nature of forces within the film. Liquid films obtained from solutions of biomolecules deserved special attention because of their relevance in biomedical and pharmacological applications. The problem of thin film stability involving liquid crystals and lubricants has also been addressed. Wetting films can provide information on the equilibrium surface forces in the liquid film bounded by two different bulk phases, a solid substrate and a gas phase. The force of interaction of film interfaces equals the disjoining pressure acting within the film. The disjoining pressure derives from several contributions, namely, London dispersion forces, electrostatic double layer forces, and structural forces. The relative importance of each component depends on the nature of the system. Most investiga-tions have been carried out with aqueous systems where the dispersion forces are negligible in comparison with the electrical double layer forces. However, for nonaqueous systems, the dispersion forces are known to control the stability of the liquid film. The confinement of a liquid between two walls induces a molecular layering that is responsible for oscillatory forces designated by structural forces. In a recent review, Boinovich 3 summarized different theoretical approaches to explain the nature of hydration, solvation, or structural repulsive forces as well as hydrophobic attractive forces as a result of deviations of various structural parameters of the thin interlayer from the corresponding values in the bulk. Room-temperature ionic liquids (RTILs) present a rare opportunity to study the interplay among a wide range of molecular interactions such as Coulombic, van der Waals, dipoleÀ dipole, hydrogen-bonding, and solvation forces. Furthermore, they are strongly promising materials in applied science because of the possibility of tuning their physicochemical properties according to the pretended application. Although the vast majority of processes in applications of RTILs involve solidÀliquid interfaces, the amount of research in this area is still scarce. Previous studies were based on sum-frequency vibrational spec-troscopy (SFVS), 4 X-ray reflectivity, 5À7 atomic force microscopy (AFM), 8À12 and also molecular simulations. 13À15 These studies had as a common objective the determination of the structure of the ionic liquid near the solid surface. To our knowledge, there are no studies in the literature concerning the interactions in thin ionic liquid films and the kinetics of thinning and rupture. The objective of the present work was to investigate the stability of wetting films of two well-known ionic liquids, 1-octyl-3-methy-limidazolium tetrafluoroborate, [C 8 mim][BF4], and 1-ethanol-3-methylimidazolium tetrafluoroborate, [C 2 OHmim][BF 4 ], in a wide
The Journal of Physical Chemistry C 08/2011; 115:16116-16123. · 4.80 Impact Factor
-
Marisa A A Rocha,
Carlos F R A C Lima,
Lígia R Gomes,
Bernd Schröder,
João A P Coutinho,
Isabel M Marrucho,
José M S S Esperança,
Luís P N Rebelo, Karina Shimizu,
José N Canongia Lopes,
Luís M N B F Santos
[show abstract]
[hide abstract]
ABSTRACT: For the first time, two distinct trends are clearly evidenced for the enthalpies and entropies of vaporization along the [Cnmim][Ntf2] ILs series. The trend shifts observed for Δ(l)(g)H(m)(o) and Δ(l)(g)S(m)(o), which occur at [C6mim][Ntf2], are related to structural modifications. The thermodynamic results reported in the present article constitute the first quantitative experimental evidence of the structural percolation phenomenon and make a significant contribution to better understanding of the relationship among cohesive energies, volatilities, and liquid structures of ionic liquids. A new Knudsen effusion apparatus, combined with a quartz crystal microbalance, was used for the high-accuracy volatility study of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series ([Cnmim][Ntf2], where n = 2, 3, 4, 5, 6, 7, 8, 10, 12). Vapor pressures in the (450–500) K temperature range were measured, and the molar standard enthalpies, entropies, and Gibbs energies of vaporization were derived. The thermodynamic parameters of vaporization were reported, along with molecular dynamic simulations of the liquid phase structure, allowing the establishment of a link between the thermodynamic properties and the percolation phenomenon in ILs.
The Journal of Physical Chemistry B 08/2011; 115(37):10919-26. · 3.70 Impact Factor
-
Marisa A. A. Rocha,
Carlos F. R. A. C. Lima,
Lígia R. Gomes,
Bernd Schröder,
João A. P. Coutinho,
Isabel M. Marrucho,
José M. S. S. Esperança,
Luís P. N. Rebelo, Karina Shimizu,
José N. Canongia Lopes,
Luís M. N. B. F. Santos
[show abstract]
[hide abstract]
ABSTRACT: For the first time, two distinct trends are clearly evidenced for the enthalpies and entropies of vaporization along the [Cnmim][Ntf2] ILs series. The trend shifts observed for ΔlgHmo and ΔlgSmo, which occur at [C6mim][Ntf2], are related to structural modifications. The thermodynamic results reported in the present article constitute the first quantitative experimental evidence of the structural percolation phenomenon and make a significant contribution to better understanding of the relationship among cohesive energies, volatilities, and liquid structures of ionic liquids. A new Knudsen effusion apparatus, combined with a quartz crystal microbalance, was used for the high-accuracy volatility study of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series ([Cnmim][Ntf2], where n = 2, 3, 4, 5, 6, 7, 8, 10, 12). Vapor pressures in the (450–500) K temperature range were measured, and the molar standard enthalpies, entropies, and Gibbs energies of vaporization were derived. The thermodynamic parameters of vaporization were reported, along with molecular dynamic simulations of the liquid phase structure, allowing the establishment of a link between the thermodynamic properties and the percolation phenomenon in ILs.
The Journal of Physical Chemistry B 08/2011; 115:10919. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The stability of wetting films of two ionic liquids, 1-octyl-3-methylimidazolium tetrafluoroborate, [C8mim][BF4], and 1-ethanol-3-methylimidazolium tetrafluoroborate, [C2OHmim][BF4], on alumina was assessed through the measurement of disjoining pressure isotherms, which represent the dependence of the disjoining pressure on the film thickness. Two experimental techniques were used at low and high disjoining pressure, respectively: captive bubble and modified thin film pressure balance. Theoretical predictions of the disjoining pressure isotherms were made using the microscopic approach of London and Hamaker based on the van der Waals contribution to the disjoining pressure. Good agreement was found between the experimental and the theoretical isotherms for [C8mim][BF4], whereas in the case of [C2OHmim][BF4], the experimental data are slightly shifted toward larger thickness, especially at higher disjoining pressures. An interpretation of these results is given in terms of a corresponding-states principle argument applied to the surface tension and the use of auxiliary molecular dynamics data. The conclusion is that although both Coulomb and dispersion interactions contribute to determine the bulk properties of these ionic liquids the surface properties are mainly related to the dispersive forces.
07/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The vaporization of a dicationic ionic liquid at moderate temperatures and under reduced pressures--recently studied by line-of-sight mass spectrometry--was further analyzed using an ion-cyclotron resonance mass spectroscopy technique that allows the monitoring of the different species present in the gas phase through the implementation of controlled ion-molecule reactions. The results support the view that the vapour phase of an aprotic dicationic ionic liquid is composed of neutral ion triplets (one dication attached to two anions). Molecular dynamics simulations were also performed in order to explain the magnitude of the vaporization enthalpies of dicationic ionic liquids vis-à-vis their monocationic counterparts.
ChemPhysChem 11/2010; 11(17):3673-7. · 3.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Despite many previous important contributions to the characterization of the liquid-liquid phase behavior of ionic liquids (ILs) plus water systems, a gap still exists as far as the effect of isomers (of ILs) is concerned. Therefore, in this work, a comprehensive study of the liquid-liquid equilibria between water and isomeric pyridinium-based ionic liquids has been performed. Atmospheric pressure mutual solubilities between water and pyridinium-based ionic liquids combined with the common anion bis[(trifluoromethyl)sulfonyl]imide were experimentally determined between (288.15 and 318.15) K. The main goal of this work is to study the isomeric effects on the pyridinium-based cation, namely, the structural and positional isomerism, as well as the alkyl side chain length. To the best of our knowledge, the influence of both structural and positional isomerism on the liquid-liquid behavior in ionic-liquid-water-containing systems is an unexplored field and is here assessed for the first time. Moreover, from the experimental solubility data, several infinite dilution molar thermodynamic functions of solution, namely, the Gibbs energy, the enthalpy, and the entropy, were estimated and discussed. In addition, aiming at gathering a broader picture of the underlying thermodynamic solvation phenomenon, molecular dynamics simulations were also carried out for the same experimental systems.
The Journal of Physical Chemistry B 11/2010; 114(48):15925-34. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Our previous simulation studies on the nanostructuration of ionic liquids are extended to the homologous series of trialkylmethylammonium bis(trifluoromethanesulfonyl)amide ionic liquids-[N(1 n n n)][NTf(2)] (n = 4, 6, and 8)-recently studied by Pott and Méléard using small-angle X-ray scattering. Comparisons between experimental and simulation results allowed us to conclude that ionic liquids of this and other homologous series with sufficiently large alkyl side chains are nanostructured media composed by polar and nonpolar domains and that their complex structure can be further subdivided according to different classes of morphology (globular, filamentous, stratified). These different topologies are a result of the specific ionic frames and interactions, characteristics of each type of cation and anion present in the homologous series.
The Journal of Physical Chemistry B 11/2010; 114(47):15635-41. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this study we have used molecular dynamics simulations to understand at the molecular level the causes for the quasi-ideal behavior of mixtures of two ionic liquids having two cations of the same homologous series and a common anion. For this purpose, we have modeled an equimolar mixture of 1-ethyl-3-methylimidazolium and 1-hexyl-3-methylimidazolium bistriflamide, ([C 2 mim][NTf 2 ] +[C 6 mim][NTf 2 ]) at 303 K and p = 0.1 MPa and analyzed its structure using the corresponding pair radial distribution functions obtained from the simulation trajectories. For comparison purposes we have also carried-out simulations under the same conditions of the two pure ionic liquids used in the mixture and also of the ionic liquid 1-butyl-3-methylimidazolium bistriflamide, [C 4 mim][NTf 2 ]. The estimated excess volume of the mixture, showing a very small deviation, agrees with experimental results.
Journal of Molecular Liquids 08/2010; 153:52-56. · 1.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Molecular dynamics simulations were used to calculate the density and the cohesive molar internal energy of seventeen different ionic liquids in the liquid phase. The results were correlated with previously reported experimental density and molar refraction data. The link between the dispersive component of the total cohesive energy of the fluid and the corresponding molar refraction was established in an unequivocal way. The results have shown that the two components of the total cohesive energy (dispersive and electrostatic) exhibit strikingly different trends and ratios along different families of ionic liquids, a notion that may help explain their diverse behavior toward different molecular solutes and solvents.
The Journal of Physical Chemistry B 04/2010; 114(17):5831-4. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this article, the fifth of a series that describes the parametrization of a force field for the molecular simulation of ionic liquids within the framework of statistical mechanics, we have modeled cations belonging to the hydroxyethylimidazolium, dimethoxy-2-methylimidazolium, and fluoroalkylimidazolium families and anions of the bis(fluorosulfonyl)amide, perfluoroalkanesulfonylamide, and fluoroalkylfluorophosphate families. The development of the force field, created in the spirit of the OPLS-AA model in a stepwise manner and oriented toward the calculation of equilibrium thermodynamic and structural properties in the liquid and crystalline phases, is discussed in detail. Because of the transferability of the present force field, the ions studied here can be combined with those reported in our four previous publications to create a large variety of ionic liquids that can be studied by molecular simulation. The present extension of the force field was validated by comparison of simulation results with experimental crystal structure and liquid density data.
The Journal of Physical Chemistry B 02/2010; 114(10):3592-600. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The concept that ionic liquids are nano-segregated fluids has allowed the rationalization at a molecular level of many of their complex and unusual properties, either as pure substances or as solvents. In this work we will use molecular dynamics simulation results to discuss in a semi-quantitative manner differ-ent aspects of such segregation: how it varies within a homologous ionic liquid family; the influence of the nature of the ions in the morphology of the segregated domains; and the interactions of those domains with molecular solutes or solvents.
Journal of Molecular Structure THEOCHEM 01/2010; 946:70-76. · 1.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The temperature-composition phase diagrams of 40 binary mixtures composed of a haloalkane dissolved in either 1-ethyl-3-methylimidazolium ethylsulfate or 1-ethyl-3-methylimidazolium ethylsulfonate were measured from ambient temperature to the boiling point temperature of the solute. The coexistence curves corresponding to liquid-liquid equilibria (LLE) boundaries were visually determined and the experimental results have been correlated using either the nonrandom two-liquid (NRTL) model or a set of empirical equations capable of describing the corresponding upper critical solution temperatures (UCSTs) loci. The different types of LLE behavior were discussed in terms of the type of ionic liquid solvent, the alkyl-chain length of the solute, and the type and pattern of halogen substitution present in the haloalkane. Auxiliary simulation data (obtained by ab initio or by molecular dynamics methods) were used to corroborate some of the experimental findings. Also, they correlate in a semiquantitative way the observed LLE behavior with the dipole moments of the different solutes.
The Journal of Physical Chemistry B 01/2010; 114:7329-7337. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this study we have used molecular dynamics simulations to understand at the molecular level the causes for the quasi-ideal behavior of mixtures of two ionic liquids having two cations of the same homologous series and a common anion. For this purpose, we have modeled an equimolar mixture of 1-ethyl-3-methylimidazolium and 1-hexyl-3-methylimidazolium bistriflamide, ([C 2 mim][NTf 2 ] +[C 6 mim][NTf 2 ]) at 303 K and p = 0.1 MPa and analyzed its structure using the corresponding pair radial distribution functions obtained from the simulation trajectories. For comparison purposes we have also carried-out simulations under the same conditions of the two pure ionic liquids used in the mixture and also of the ionic liquid 1-butyl-3-methylimidazolium bistriflamide, [C 4 mim][NTf 2 ]. The estimated excess volume of the mixture, showing a very small deviation, agrees with experimental results.
Journal of Molecular Liquids 08/2009; · 1.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The diverse dipole and quadrupole moments of benzene and its 12 fluorinated derivatives are correlated to their solubility in the ionic liquid 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide. Albeit empirical, the correlation was built taken into account molecular insights gained from ab initio calculations of the isolated aromatic solute molecules and molecular dynamics simulations of all 13 aromatic solute plus ionic liquid solvent binary mixtures. This type of molecular-assisted approach unveiled a simple correlation between the dipole and quadrupole moments of the solutes and the ionic liquid solvent. It also revealed the complex nature of the interactions between aromatic compounds and ionic liquids, with the charge density functions of the former acting as a sort of molecular template that promotes the segregation of the ions of the latter and defines the fluid phase behavior (liquid-liquid demixing) of the corresponding binary mixtures. Such an approach can be extended to other systems involving the interactions of different types of solutes with ionic liquid solvents.
The Journal of Physical Chemistry B 08/2009; 113(29):9894-900. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This work extends the scope of previous studies on the phase behavior of mixtures of ionic liquids with benzenes or its derivatives by determining the solid-liquid and liquid-liquid phase diagrams of mixtures containing an ionic liquid and a fluorinated benzene. The systems studied include 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide plus hexafluorobenzene or 1,3,5-trifluorobenzene and 1-ethyl-3-methylimidazolium triflate or N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide plus benzene. The phase diagrams exhibit different kinds of solid-liquid behavior: the (usual) occurrence of eutectic points; the (not-so-usual) presence of congruent melting points and the corresponding formation of inclusion crystals; or the observation of different ionic liquid crystalline phases (polymorphism). These different types of behavior can be controlled by temperature annealing during crystallization or by the nature of the aromatic compound and can be interpreted, at a molecular level, taking into account the structure of the crystals or liquid mixtures, together with the unique characteristics of ionic liquids, namely the dual nature of their interactions with aromatic compounds.
The Journal of Physical Chemistry B 06/2009; 113(21):7631-6. · 3.70 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The red flavylium cations of anthocyanins form ground-state charge-transfer complexes with several naturally occurring electron-donor copigments, such as hydroxylated flavones and hydroxycinnamic or benzoic acids. Excitation of the 7-methoxy-4-methyl-flavylium-protocatechuic acid complex results in ultrafast (240 fs) internal conversion to the ground state of the complex by way of a low-lying charge-transfer state. Thus, both uncomplexed anthocyanins, whose excited state decays by fast (5-20 ps) excited-state proton transfer, and anthocyanin-copigment complexes have highly efficient mechanisms of deactivation that are consistent with the proposed protective role of anthocyanins against excess solar radiation in the vegetative tissues of plants.
Chemistry 01/2009; 15(6):1397-402. · 5.93 Impact Factor
