Effect of acetonitrile on the solubility of carbon dioxide in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide

The effect of the addition of acetonitrile on the solubility of carbon dioxide in an ionic liquid, the 1-ethyl-3- methylimidazolium bis(trifluoromethanesulfonyl)amide, [C(2)mim][NTf2], was studied experimentally at pressures close to atmospheric and as a function of temperature between 290 and 335 K. It was observed that the solubility of carbon dioxide decreases linearly with the mole fraction of acetonitrile from a value of 2.6 x 10(-2) in the pure ionic liquid at 303 K to a mole fraction of 1.3 x 10(-2) in the mixture [C(2)mim][NTf2] + CH3CN with x(CH3CN) = 0.77 at the same temperature. The gas solubility decreases with temperature, and the thermodynamic properties of solvation could be calculated. The vapor pressures of the [ C2mim][ NTf2] + CH3CN mixtures were measured in the same temperature range, and strong negative deviations from Raoult's law were obtained: up to 36% for a mixture with x(CH3CN) = 0.46 at 334 K. Negative excess molar volumes of approximately -1 cm(3) mol(-1) at equimolar composition could also be calculated from density measurements of the pure components and of the mixtures. These observations are confirmed by neutron diffraction studies and are compatible with the existence of strong ion-dipole interactions in the mixed liquid solvent.

Phase Behaviour, Interactions, and Structural Studies of (Amines+Ionic Liquids) Binary Mixtures

We present a study on the phase equilibrium behaviour of binary mixtures containing two 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide-based ionic liquids, [Cnmim] [NTf2] (n=2 and 4), mixed with diethylamine or triethylamine as a function of temperature and composition using different experimental techniques. Based on this work, two systems showing an LCST and one system with a possible hourglass shape are measured. Their phase behaviours are then correlated and predicted by using Flory–Huggins equations and the UNIQUAC method implemented in Aspen. The potential of the COSMO-RS methodology to predict the phase equilibria was also tested for the binary systems studied. However, this methodology is unable to predict the trends obtained experimentally, limiting its use for systems involving amines in ionic liquids. The liquid-state structure of the binary mixture ([C2mim] [NTf2]+diethylamine) is also investigated by molecular dynamics simulation and neutron diffraction. Finally, the absorption of gaseous ethane by the ([C2mim][NTf2]+diethylamine) binary mixture is determined and compared with that observed in the pure solvents.

Tuning solute redox potentials by varying the anion component of room temperature ionic liquids

The electrode potentials for the two one electron oxidations of 1,2-diferrocenylethylene (bisferrocene, BF) were studied relative to that of the one electrode oxidation of decamethylferrocene in a variety of RTILs. The difference in these potentials was found to be very sensitive to the anion component of the ionic liquid showing the scope of these solutes as 'designer media' to tune the thermodynamic properties of solutes dissolved in them.

Rheological and heat transfer behaviour of the ionic liquid, [C(4)mim][NTf2]

Systematic experiments have been carried out on the thermal and rheological behaviour of the ionic liquid, 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl} imide, [C(4)mim][NTf2], and, for the first time, on the forced convective heat transfer of an ionic liquid under the laminar flow conditions. The results show that the thermal conductivity of the ionic liquid is similar to 0.13 W m(-1) K-1, which is almost independent of temperature between 25 and 40 degrees C. Rheological measurements show that the [C(4)mim][NTf2] liquid is a Newtonian fluid with its shear viscosity decreasing with increasing temperature according to the exponential law over a temperature range of 20-90 degrees C. The convective heat transfer experiments demonstrate that the thermal entrance length of the ionic liquid is very large due to its high viscosity and low thermal conductivity. The convective heat transfer coefficient is observed to be much lower than that of distilled water under the same conditions. The convective heat transfer data are also found to fit well to the convectional Shah's equation under the conditions of this work. (C) 2007 Elsevier Inc. All rights reserved.

Excess molar volumes and excess molar enthalpies in binary systems N-alkyl-triethylammonium bis(trifluoromethylsulfonyl)imide plus methanol

In the present paper, a study on the influence of the alkyl chain length in N-alkyl-triethylammonium bis(trifluoromethylsulfonyl)imide ionic liquids, [N_R,222][Tf₂N] (R   = 6, 8 or 12), on the excess molar enthalpy at 303.15 K and excess molar volume within the temperature interval (283.15–338.15 K) of ionic liquid + methanol mixtures is carried out. Small excess molar volumes with highly asymmetric curves (i.e. S-shape) as a function of mole fraction composition were obtained, with negative values showing in the methanol-rich regions. The excess molar volumes increase with the increase of the alkyl-chain length of the ammonium cation of the ionic liquid and decrease with temperature. The excess enthalpies of selected binary mixtures are positive over the whole composition range and increase slightly with the length of the alkyl side-chain of the cation on the ionic liquid. Both excess properties were subsequently correlated using a Redlich–Kister-type equation, as well as by using the ERAS model. From this semipredictive model the studied excess quantities could be obtained from its chemical and physical contribution. Finally, the COSMOThermX software has been used to evaluate its prediction capability on the excess enthalpy for investigated mixtures at 303.15 K and 0.1 MPa. From this work, it appears that COSMOThermX method predicts this property with good accuracy of approx. 10%, providing at the same time the correct order of magnitude of the partial molar excess enthalpies at infinite dilution for the studied ILs,

On the scaling behavior of electric conductivity in [C(4)mim][NTf2]

In this work we examine, for the first time, the molar conductivity behavior of the deeply supercooled room temperature ionic liquid [C₄mim][NTf₂] in the temperature, pressure and volume thermodynamic space in terms of density scaling (TV^γ)⁻¹ combined with the equation of state (EOS). The exponent γ_σ determined from the Avramov model analysis is compared with the coefficient obtained from the viscosity studies carried out at moderate temperatures. Therefore, the experimental results presented herein provide the answer to the long-standing question regarding the validity of thermodynamic scaling of ionic liquids over a wide temperature range, i.e. from the normal liquid state to the glass transition point. Finally, we investigate the relationship between the dynamic and thermodynamic properties of [C₄mim][NTf₂] represented by scaling exponent γ and Grüneisen constant γ_G, respectively.

An Energy Descriptor To Quantify Methane Selectivity in Fischer-Tropsch Synthesis:A Density Functional Theory Study

Selectivity is a fundamental issue in heterogeneous catalysis. In this study, the CH(4) selectivity in Fischer-Tropsch synthesis is chosen to be investigated: CH4 selectivity on Rh, Co, Ru, Fe, and Re surfaces is computed by first-principles methods. In conjunction with kinetic analyses, we are able to derive the effective barrier difference between methane formation and chain growth (Delta E(eff)) to quantify the CH(4) selectivity. By using this energy descriptor, the ranking of methane selectivity predicted from density functional theory (DFT) calculations is consistent with experimental work. Moreover, a linear correlation between Delta E(eff) and the chemisorption energy of C + 4H (Delta H) is found. This fundamental finding possesses the following significance: (i) it shows that the selectivity, which appears to have kinetic characteristics, is largely determined by thermodynamic properties; and (ii) it suggests that an increase of the binding strength of C + 4H will suppress methane selectivity.

Artificial Neural Network for Compositional Ionic Liquid Viscosity Prediction

Being a new generation of green solvents and high-tech reaction media of the future, ionic liquids have increasingly attracted much attention. Of particular interest in this context are room temperature ionic liquids (in short as ILs in this paper). Due to the relatively high viscosity, ILs is expected to be used in the form of solvent diluted mixture with reduced viscosity in industrial application, where predicting the viscosity of IL mixture has been an important research issue. Different IL mixture and many modelling approaches have been investigated. The objective of this study is to provide an alternative model approach using soft computing technique, i.e., artificial neural network (ANN) model, to predict the compositional viscosity of binary mixtures of ILs [C _n-mim][NTf ₂] with n=4, 6, 8, 10 in methanol and ethanol over the entire range of molar fraction at a broad range of temperatures from T=293.0-328.0K. The results show that the proposed ANN model provides alternative way to predict compositional viscosity successfully with highly improved accuracy and also show its potential to be extensively utilized to predict compositional viscosity taking account of IL alkyl chain length, as well as temperature and compositions simultaneously, i.e., more complex intermolecular interactions between components in which it would be hard or impossible to establish the analytical model. This illustrates the potential application of ANN in the case that the physical and thermodynamic properties are highly non-linear or too complex. © 2012 Copyright the authors.

Monte Carlo simulation of properties of monolayers and metal islands adsorbed on metallic (111) surfaces

To obtain the surface stress changes due to the adsorption of metal monolayers onto metallic surfaces, a new model derived from thermodynamic considerations is presented. Such a model is based on continuum Monte Carlo simulations with embedded atom method potentials in the canonical ensemble, and it is extended to consider the behavior on different islands adsorbed onto (111) substrate surfaces. Homoepitaxial and heteroepitaxial systems are studied. Pseudomorphic growth is not observed for small metal islands with considerable positive misfit with the substrate. Instead, the islands become compressed upon increase of their size. A simple model is proposed to interpolate between the misfits of atoms in small islands and the pseudomorphic behavior of the monolayer.

Neutral and Charged 1-Butyl-3-methylimidazolium Triflate Clusters: Equilibrium Concentration in the Vapor Phase and Thermal Properties of Nanometric Droplets

Ground state energy, structure, and harmonic vibrational modes of 1-butyl-3-methylimidazolium triflate ([bmim][Tf]) clusters have been computed using an all-atom empirical potential model. Neutral and charged species have been considered up to a size (30 [bmim][Tf] pairs) well into the nanometric range. Free energy computations and thermodynamic modeling have been used to predict the equilibrium composition of the vapor phase as a function of temperature and density. The results point to a nonnegligible concentration of very small charged species at pressures (P ~ 0.01 Pa) and temperatures (T 600 K) at the boundary of the stability range of [bmim][Tf]. Thermal properties of nanometric neutral droplets have been investigated in the 0 T 700 K range. A near-continuous transition between a liquidlike phase at high T and a solidlike phase at low T takes place at T ~ 190 K in close correspondence with the bulk glass point Tg ~ 200 K. Solidification is accompanied by a transition in the dielectric properties of the droplet, giving rise to a small permanent dipole embedded into the solid cluster. The simulation results highlight the molecular precursors of several macroscopic properties and phenomena and point to the close competition of Coulomb and dispersion forces as their common origin.

Thermodynamic Studies of Ionic Interactions in Aqueous Solutions of Imidazolium-Based Ionic Liquids [Emim][Br] and [Bmim][Cl]

Experimental measurements of density at different temperatures ranging from 293.15 to 313.15 K, the speed of sound and osmotic coefficients at 298.15 K for aqueous solution of 1-ethyl-3-methylimidazolium bromide ([Emim][Br]), and osmotic coefficients at 298.15 K for aqueous solutions of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) in the dilute concentration region are taken. The data are used to obtain compressibilities, expansivity, apparent and limiting molar properties, internal pressure, activity, and activity coefficients for [Emim][Br] in aqueous solutions. Experimental activity coefficient data are compared with that obtained from Debye-Hückel and Pitzer models. The activity data are further used to obtain the hydration number and the osmotic second virial coefficients of ionic liquids. Partial molar entropies of [Bmim][Cl] are also obtained using the free-energy and enthalpy data. The distance of the closest approach of ions is estimated using the activity data for ILs in aqueous solutions and is compared with that of X-ray data analysis in the solid phase. The measured data show that the concentration dependence for aqueous solutions of [Emim][Br] can be accounted for in terms of the hydrophobic hydration of ions and that this IL exhibits Coulombic interactions as well as hydrophobic hydration for both the cations and anions. The small hydration numbers for the studied ILs indicate that the low charge density of cations and their hydrophobic nature is responsible for the formation of the water-structure-enforced ion pairs.

Computational Verification of Two Universal Relations for Simple Ionic Liquids. Kinetic Properties of a Model 2:1 Molten Salt

Two semianalytical relations [Nature, 1996, 381, 137 and Phys. Rev. Lett. 2001, 87, 245901] predicting dynamical coefficients of simple liquids on the basis of structural properties have been tested by extensive molecular dynamics simulations for an idealized 2:1 model molten salt. In agreement with previous simulation studies, our results support the validity of the relation expressing the self-diffusion coefficient as a Function of the radial distribution functions for all thermodynamic conditions such that the system is in the ionic (ie., fully dissociated) liquid state. Deviations are apparent for high-density samples in the amorphous state and in the low-density, low-temperature range, when ions condense into AB(2) molecules. A similar relation predicting the ionic conductivity is only partially validated by our data. The simulation results, covering 210 distinct thermodynamic states, represent an extended database to tune and validate semianalytical theories of dynamical properties and provide a baseline for the interpretation of properties of more complex systems such as the room-temperature ionic liquids.

Microstructure and mechanical properties of low nickel maraging steel

Austenitization with lower temperature and intercritical annealing were introduced in the treatment of a maraging steel with a composition of Fe–12.94Ni–1.61Al–1.01Mo–0.23Nb (wt.%). Scanning electron microscopy was employed to study the microstructure after austenitization at 950 °C and intercritical annealing, followed by aging at 485 and 600 °C. X-ray diffraction (XRD) analysis was applied to evaluate the formation of retained or reverted austenite. Thermodynamic calculation was employed to calculate equilibrium phase mole fractions. Hardness and Charpy impact toughness of the steel were measured. Intercritical annealing treatments did not result in significant increase of hardness either before or after aging. The Charpy impact toughness of the alloy in aged condition was enhanced after austenitization at 950 °C. No austenite was observed in XRD. However, suspected reverted austenite was found after austenitization at 950 °C followed by aging at 600 °C for 4 h. Relationships among heat treatment, microstructure and mechanical properties are discussed.

Thermophysical properties, low pressure solubilities and thermodynamics of solvation of carbon dioxide and hydrogen in two ionic liquids based on the alkylsulfate anion

Densities and viscosities of the ionic liquid 1-butyl-3-methylimidazolium octylsulfate, [C4C1Im][C8SO4] were measured as a function of temperature between 313 K and 395 K. Solubilities of hydrogen and carbon dioxide were determined, between 283 K and 343 K, and at pressures close to atmospheric in [C4C1Im][C 8SO4] and in another ionic liquid based on the alkylsulfate anion-1-ethyl-3-methylimidazolium ethylsulfate, [C 2C1Im][C2SO4]. Density and viscosity were measured using a vibrating tube densimeter from Anton Paar and a rheometer from Rheometrics Scientific with accuracies of 10-3 g cm -3 and 1%, respectively. Solubilities were obtained using an isochoric saturation technique and, from the variation of solubility with temperature, the partial molar thermodynamic functions of solvation, such as the standard Gibbs energy, the enthalpy, and the entropy, are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations, is better than ±1%. © The Royal Society of Chemistry.

Infection-Responsive Drug Delivery from Urinary Biomaterials Controlled by a Novel Kinetic and Thermodynamic Approach

Purpose. The pH-dependent physicochemical properties of the antimicrobial quinolone, nalidixic acid, were exploited to achieve ‘intelligent’ drug release from a potential urinary catheter coating, poly(2-hydroxyethylmethacrylate) (p(HEMA)), in direct response to the elevated pH which occurs at the onset of catheter infection.
Methods. p(HEMA) hydrogels, and reduced-hydrophilicity copolymers incorporating methyl methacrylate, were loaded with nalidixic acid by a novel, surface particulate localization method, and characterized in terms of pH-dependent drug release and microbiological activity against the common urease-producing urinary pathogen Proteus mirabilis.
Results. The pH-dependent release kinetics of surface-localized nalidixic acid were 50- and 10-fold faster at pH 9, representing the alkaline conditions induced by urease-producing urinary pathogens, compared to release at pH 5 and pH 7 respectively. Furthermore, microbiological activity against P. mirabilis was significantly enhanced after loading surface particulate nalidixic acid in comparison to p(HEMA) hydrogels conventionally loaded with dispersed drug. The more hydrophobic methyl methacrylate-containing copolymers also demonstrated this pH responsive behavior, but additionally exhibited a sustained period of zero-order release.
Conclusions. The paradigm presented here provides a system with latent, immediate infection-responsive drug release followed by prolonged zero-order antimicrobial delivery, and represents an ‘intelligent’, infection-responsive, self-sterilizing biomaterial.