Vapor Pressure Of Ionic Liquids Research Articles

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]+ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

Ionic Liquids as Alternative Curing Agents for Conductive Epoxy/CNT Nanocomposites with Improved Adhesive Properties

Good dispersion of carbon nanotubes (CNTs) together with effective curing were obtained in epoxy/CNT nanocomposites (NCs) using three different ionic liquids (ILs). Compared to conventional amine-cured epoxy systems, lower electrical percolation thresholds were obtained in some of the IL-based epoxy systems. For example, the percolation threshold of the trihexyltetradecylphosphonium dicyanamide (IL-P-DCA)-based system was 0.001 wt.%. The addition of CNTs was not found to have any significant effect on the thermal or low-strain mechanical properties of the nanocomposites, but it did improve their adhesive properties considerably compared to the unfilled systems. This study demonstrates that ILs can be used to successfully replace traditional amine-based curing agents for the production of electrically conductive epoxy/CNT NCs and adhesives, as a similar or better balance of properties was achieved. This represents a step towards greater sustainability given that the vapor pressure of ILs is low, and the amount needed to effectively cure epoxy resins is significantly lower than any of their counterparts.

An empirical correlation for predicting vapor pressure of ionic liquids

The accuracy of vapor pressure calculations is essential because it is used as a basis to estimate the thermal and equilibrium properties in energy industries. In this research work, a new empirical model for predicting the vapor pressure of ionic liquids is presented. The model was derived from 383 experimental data points of the vapor pressure of 32 different ionic liquids, as a function of temperature, critical pressure, critical temperature, acentric factor, critical compressibility factor, the number of carbons of the second alkyl group of the cation, mass connectivity index and molecular weight. The computational parameters have been determined using extended group contribution methods. The accuracy of the new model has been calculated by the absolute relative deviation percent (AARD%) of 6.82. The comparison between the current study and previous studies indicates that the proposed method provides more accurate results compared to other methods.

An Empirical Correlation for Predicting Vapor Pressure of Ionic Liquids

An Empirical Correlation for Predicting Vapor Pressure of Ionic Liquids

Bio-based, self-adhesive, and self-healing ionogel with excellent mechanical properties for flexible strain sensor.

Bio-based ionogels with versatile properties are highly desired for practical applications. Herein, we designed a novel self-healing, anti-freezing, and self-adhesive ionogel with excellent sensor capability. The ionogel was obtained by cross-linking amino groups (chitosan) and aldehyde groups (dextran oxide) to form Schiff-base bonds in the ionic liquids (EMIMOAc) with TA. Ionogels inherited the superior electrical conductivity of ionic liquids (IG2, 1.1 mS cm−1). Due to the dynamic reaction of Schiff-base bonds, the obtained IG2 possessed self-healing properties (self-healing efficiency = 89%). The presence of TA also provided the ionogel with excellent self-adhesive properties (IG2/TA, adhesive strength to hogskin = 8.05 kPa). Owing to the low freezing point and low vapor pressure of ionic liquids, ionogels were endowed with anti-freeze properties and resistance to solvent volatility. Moreover, the ionogel can act as a strain sensor, and exhibited excellent sensitivity and sensing performance. Our work provided a green and effective method in preparation of the high performance ionogel sensor, which could accommodate future practical industrial applications.

Zero-insertion-loss optical shutter based on electrowetting-on-dielectric actuation of opaque ionic liquid microdroplets

This article reports a broad-band optical shutter based on microdroplet actuation with zero optical insertion loss in the open state. These features are achieved by electrowetting-on-dielectric (EWOD) actuation of opaque ionic liquid microdroplets. The negligible vapor pressure of ionic liquids allows the device to robustly operate in open air, unlike previously proposed EWOD-based systems in which the light crosses several attenuating and reflective layers, preventing broad-band operation and creating insertion losses > 14%. The presented device provides an attenuation of 78 dB in the closed state and a transmission of >99.99999% in the open state and can operate in the visible and mid-infrared wavelength range. Moreover, the switch can sustain larger incoming laser powers (5 mW continuous exposure or up to 3 h of continuous exposure at ∼100 mW) compared to the values reported for other state-of-the-art EWOD-based shutters. Additionally, the proposed device is compact, operates with low voltage (<25 V peak voltage), and features zero static power consumption.

Development of the Knudsen effusion methodology for vapour pressure measurements of low volatile liquids and solids based on a quartz crystal microbalance

The principle of operation, concepts and recent developments of the Knudsen effusion methodology for the vapour pressure measurement of ionic liquids and other low volatile liquids and solids are presented. A new version of a Knudsen effusion apparatus, coupled with a quartz crystal microbalance, which is used for a reliable measurement of the mass flow from a Knudsen effusion cell, is described in detail. In the new system, designed and optimized for the vapour pressure measurement of ionic liquids, it is possible to measure the vapour pressure of small samples using very short effusion time over a wide temperature range. This apparatus allows the vapour pressure measurements using step-temperature and continuous-temperature modes that have the advantage of reducing the measurement time interval and minimize the effect of a sample degradation. A significant number of improvements on the performance and capability for the vapour pressure measurements of ionic liquids has been implemented: in situ temperature control of the vacuum chamber for a better stability of background signal; a new design of a stainless steel effusion cell to decrease the reactivity and sample decomposition; dual temperature control ensuring a positive temperature gradient between bottom and top of the cell in order to avoid the ionic liquids condensation on the effusion cell lid and significantly improved stability of the time frequency derivative at high temperatures; Installation and test of a mass flow tube, on the top of the outlet of the cell lid oven block in order to increase the mass sensitivity coefficient of QCM. The tests and benchmarking concerning the measurement of vapour pressures of ionic liquids performed with [C2mim][NTf2] indicate that the described Knudsen effusion apparatus and methodology is able to produce reproducible and reliable experimental vapour pressure data with an accuracy and quality similar than the achieved in the measurements with low volatile solids. The effect of the improvements on the performance of the Knudsen effusion apparatus was tested and evaluated by the comparison of the vapour pressure results of 1,3,5-triphenylbenzene and 1-ethyl-3-methylimidazolium with the available literature data.

Reaction-Based Detection of Chemical Warfare Agent Mimics with Affinity Ionic Liquids.

We are demonstrating here the successful development of an ionic liquid device based on affinity ionic liquids AIL 1-6 tailored for chemoselective detection of gaseous chemical warfare agent (CWA) mimics on a quartz crystal microbalance (QCM) as well as on disposable filter papers. In the QCM platform, the negligible vapor pressure of ionic liquids ensures that AILs do not dry out on quartz chips and are used free of leakage during the measurements. This lack of vapor pressure makes these ionic liquid devices highly attractive for gas analysis. In the present study, chemoselective CWA mimic vapor detection by QCM occurs when gas rapidly diffuses into the AIL thin film and accordingly the nucleophilic substitution reaction emerges under the experimental conditions developed. Our initial results give credence to three important conclusions: (i) AILs could be prepared in short synthetic steps and are remarkable in detecting CWA mimics, (ii) the analysis of gaseous CWA mimics on QCM is label-free and chemoselective, and (iii) the detection of CWA mimic vapor by AILs on filter paper discs is colorimetric and portable, and, once used, the paper disc can be disposed. To the best of our knowledge, this is the first report in the literature based on the CWA mimic vapor detection in ionic liquids on a QCM.

SEM as a Facile Tool for Real-Time Monitoring of Microcrystal Growth during Electrodeposition: The Merit of Ionic Liquids.

Due to the extremely low vapor pressure of ionic liquids (ILs), electrochemical deposition/dissolution of hexagonal hollow CuSn alloy tubes in IL can be real-time observed with a scanning electron microscope (SEM). Two specially made electrochemical cells are used for the top-view and side-view observations. A series of clear SEM images reveals the hexagonal cones are formed prior to further developing hexagonal tubes. At the beginning, many small nuclei are formed on the electrode surface. Due to the electrodeposition rate being slow enough for the nuclei to crystallize into hexagonal structures, the electrodeposition rate is faster on the periphery than the inside of the structures. As the electrodeposition progresses, the tube wall will grow thicker, and a secondary tube emerges inside the primary tube. Finally, shell-by-shell hexagonal tubes are formed. Furthermore, the in situ SEM observation also reveals that the dissolution of tube starts from its inner wall followed by a sudden collapse of its wall. In this paper, we establish a simple and convenient method, which can be broadly applied to the study of metal, alloy, and semiconductor growth in real time.

On the prediction of the vapor pressure of ionic liquids based on the principle of corresponding states

The complexity, coupled with the high cost of the experimental determination of the vapor pressure of pure ionic liquids (ILs), which at moderate temperatures typically assume values below 0.1(Pa), make the development of predictive models for this important thermophysical property crucial. Employing 309 experimental data points belonging to 20 ILs of different classes and based on the truncated Pitzer expansion, in the current work a simple analytical expression has been developed for the prediction of the vapor pressure of pure ILs. In doing so, all the required critical properties have been estimated using a well-known group contribution method. Subsequently, utilizing the Clausius-Clapeyron equation, a very simple expression has been derived for the prediction of the enthalpy of vaporization of ILs. Total AARDs of 6.97% in the prediction of the available experimental vapor pressure data, and of 5.89% in the prediction of the molar heat of vaporization of 62 ILs demonstrate the satisfactory accuracy and predictive performance of the model developed in the current study. A thorough comparison has also been made with two previously published generalized expressions based on the zero-pressure liquid fugacity approach, through which the superiority of the proposed model has been established.

Preparation and Properties of C═X (X: O, N, S) Based Distillable Ionic Liquids and Their Application for Rare Earth Separation

The negligible vapor pressure of ionic liquids prevents the separation of ionic liquids from other nonvolatile substances by distillation. Most distillable ionic liquids have been reported are protic ionic liquids, and the aprotic ionic liquids are still scarce. In this work, we designed and synthesized a series of unsaturated bond (C═X; X is O, N, S) based ionic liquids and some of them could be distilled at a mild condition. Moreover, [MDMF]TfO shows a high efficiency for separation of EuCl3 from the mixture of EuCl3 and NdCl3.

Improved Electrocatalytic Oxidation of Urea Using Ru-Ni Binary Nanoparticles Prepared By an Ionic Liquid/Metal Sputtering Technique

Introduction Direct urea fuel cells are attracting as next generation power sources due to the high energy density, safety, and ease of transportation of urea in comparison with other candidate sources for fuel cells, such as hydrogen, alcohols and ammonia. Botte and co-workers reported that nickel electrodes exhibited electrocatalytic activity for urea oxidation in basic aqueous solution.[1] However further improvement in stability and activity for catalysts is necessary to achieve practical use. Recently we have reported the facile preparation of metal and alloy nanoparticles in ionic liquids without additional stabilizing agents using metal sputter deposition technique.[2]The extremely low vapor pressure of ionic liquids enables the sputter deposition of metal species onto the ionic liquids under reduced pressure. Noble metal nanoparticles of several nanometers in size, such as Au, Pd, and Pt, were successfully prepared by sputtering the corresponding metal targets, while simultaneous sputter deposition of different metals produced alloy nanoparticles such as AuPd and AuPt. Alloy nanoparticles exhibited unique physicochemical properties distinct from those of monometallic counterparts, and their catalytic activities could be modified by the control of chemical composition of nanoparticles. Here we report the preparation of Ru-Ni binary nanoparticles by sequential sputter deposition of Ru and Ni onto ionic liquids followed by heat treatment. Furthermore the electrocatalytic activity of thus-obtained nanoparticles is investigated for urea oxidation in alkaline media. Experimental Ru-Ni binary nanoparticles were synthesized by the sequential sputter deposition of Ru and Ni metals onto ionic liquids of 1-ethyl-3-methylimidazolium tetrafuloroborate using a sputter coater (SC-701HMCII, Sanyu Electron). A portion of acetonitrile solution dispersed with carbon black (CB) particles was mixed with thus-obtained ionic liquids, followed by heat treatment at 300 ˚C for 30 min. Thus-obtained Ru-Ni nanoparticles-immobilized CB particle catalyst (Ru-Ni/CB) were isolated by centrifugation. The Ni/Ru ratio in the catalyst was controlled by changing the amount of Ru sputter-deposited in the ionic liquid. Nanoparticles of Ru and Ni, loaded on CB in a similar manner, were also prepared for comparison. The electrocatalytic activity for urea oxidation was investigated with use of grassy carbon electrodes modified with Ru-Ni/CB catalyst particles in 0.1 mol dm-3 NaOH aqueous solution containing 0.1 mol dm-3 urea. Results and discussions TEM observation of Ru-Ni/CB revealed that small Ru-Ni binary nanoparticles with average diameter of 3.9 ± 2.1 nm were densely immobilized on the surface of CB particles without formation of large aggregation as shown in the inset of Fig. 1. The chemical condition of particles loaded on CB was investigated by XPS. Ni/CB showed a single peak of Ni 2p at 856.1 eV attributable to Ni2+, indicating that Ni was completely oxidized during preparation procedure of catalyst. In contrast, the Ni 2p signals of Ru-Ni/CB appeared at 854.2 and 860.1 eV, which were assigned to Ni0 and Ni3+, respectively. This suggests that Ni oxidation was partially prevented in Ru-Ni/CB probably due to the electronic interaction between Ni and Ru atoms. Figure 1 shows cyclic voltammograms of Ru-Ni/CB, Ni/CB, and Ru/CB for urea oxidation in 0.1 mol dm-3NaOH aqueous solution. As reported previously, Ni/CB exhibited the electrocatalytic activity for urea oxidation, in which anodic current for urea oxidation was increased at the potential more positive than 0.5 V vs Ag/AgCl, though no current was observed for Ru/CB. On the other hand, urea oxidation also occurred with use of Ru-Ni/CB at the potential more positive than 0.5 V vs Ag/AgCl, the intensity being about 2 times larger than that of Ni/CB at a constant potential. These results indicated that the electrocatalytic activity for urea oxidation was higher for Ru-Ni binary particles than pure Ni particles, in spite that Ru particles had no activity. The chemical composition of Ru-Ni/CB catalyst was found to influence the catalytic activity: Volcano-type dependence was observed between Ru content in Ru-Ni/CB and the current density at 0.6 V vs. Ag/AgCl. Consequently, we concluded that electrocatalytic activity for urea oxidation of Ni particles was improved by preparing Ru-Ni binary nanoparticles in which Ru and Ni were probably mixed in atomic or nanometer scales. REFERENCES [1] Botte, et al., Electrochimica Acta, 2012, 81, 292. [2] M. Hirano, et al., Phys. Chem. Chem. Phys., 2013, 15, 7286. Figure 1

Modelling phase equilibria of pure ionic liquids from a new equation of state

A perturbed hard-trimer (PHT) equation of state (EOS) has been employed to model densities and some derived thermodynamic properties of 39 ionic liquids (ILs) considering a trimer expression obtained from the statistical associating fluid theory as the reference physical model. The van der Waals dispersion forces were applied as perturbation term. The proposed model was tested using ILs containing imidazolium, pyrrolidinium, pyridinium, phosphonium and piperidinium cations. Two parameters appeared in the PHT EOS which are temperature-dependent, reflecting the dispersive energy parameters among trimers, e and the hard-core diameter, σ, were determined based on the molecular scaling parameters. The performance of the proposed PHT EOS has been evaluated by predicting the volumetric and first and second derivatives thermodynamic properties in the pressure and temperature ranges within 0.1–200 MPa and 273–472.6 K, respectively. From 6331 data points examined, the average absolute deviation (AAD) of the correlated (at 0.1 MPa) and predicted (at high pressures) densities from the experimental ones was found to be 0.18 %. Furthermore, the isothermal compressibilities and thermal expansion coefficients as well as the heat capacities were estimated through the PHT EOS with uncertainties of the order of ±11.09, ±11.76 and ±3.34 %, respectively. Further, the vapour pressures of ILs are also predicted by the proposed model. The trend of the predicted vapour pressure is in accord with those reported in literature.

Vapor pressure of ionic liquids at low temperatures from AC-chip-calorimetry.

The very low vapor pressure of ionic liquids is challenging to measure. At elevated temperatures the liquids might start to decompose, and at relatively low temperatures the vapor pressure becomes too low to be measured by conventional methods. In this work we developed a highly sensitive method for mass loss determination at temperatures starting from 350 K. This technique is based on an alternating current calorimeter equipped with a chip sensor that consists of a free-standing SiNx-membrane (thickness <1 μm) and a measuring area with lateral dimensions of the order of 1 mm. A small droplet (diameter ca. 600 μm) of an ionic liquid is vaporized isothermally from the chip sensor in a vacuum-chamber. The surface-to-volume-ratio of such a droplet is large and the relative mass loss due to evaporation is therefore easy to monitor by the changing heat capacity (J K(-1)) of the remaining liquid. The vapor pressure is determined from the measured mass loss rates using the Langmuir equation. The method was successfully tested for the determination of the vapor pressure and the vaporization enthalpy of an archetypical ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2]). The data set created in this way in an extremely broad temperature range from 358 K to 780 K has allowed the estimation of the boiling temperature of [EMIm][NTf2]. The value (1120 ± 50) K should be considered as the first reliable boiling point of the archetypical ionic liquid obtained from experimental vapor pressures measured in the most possible close proximity to the normal boiling temperature.

Thermodynamic Behavior of Binary Mixtures of 1-Butyl-1-methylpyrrolidinium Iodide and Alcohols

In this work, the osmotic properties of the binary mixtures of 1-butyl-1-methylpyrrolidinium iodide ([BmPr][I]) with isopropanol and n-butanol were studied by using vapor pressure osmometry (VPO) technique at 323.15 K at atmospheric pressure. It was found that the values of osmotic coefficient, mean molal activity coefficient, and vapor pressure decrease with increasing molality. We observed that the change in vapor pressure of ionic liquid in n-butanol is smaller compared to ionic liquid in isopropanol. The excess Gibbs free energy of ionic liquid in isopropanol has a higher value as compared to an ionic liquid + n-butanol mixture. The binary mixture of ionic liquid with alcohols shows noticeable deviation from the Debye–Huckel limiting law. We have used the pseudophase separation model on the experimental osmotic coefficient value to estimate the critical aggregation concentration of ionic liquid in alcohols. We have showed the structural effect of the solvent on the preceding thermodynamic parameters a...

New Analytical Expression for the Prediction of Vapour Pressures of Ionic Liquids

Ionic liquids (IL), considered as green solvents, are useful in different industrial applications. Vapour pressure is one of the key properties of IL for designing different processes. Recently, the zero pressure fugacity approach was proposed to predict the vapour pressures of IL using cubic equations of state. In the present work, this approach was improved by fitting the vapour pressure data of ten ILs using six different cohesion factor models. New analytical expressions are proposed in the present work for predicting vapour pressure of IL using acentric factor and Mass Connectivity Index. It was shown that one of the proposed models (Model J) predicts vapour pressure with global %AAD of 7.3%. The model compared with the models based on COSMO-RS theory and PC SAFT-equation of state (EOS), and it was found that the proposed models work well compared to others. It is shown that the proposed models predict vapour pressure with greater accuracy and consistency.

Are ionic liquids extremophiles cell wall breakers? Esther Gutiérrez, M. Ángeles Sanromán, Ana Rodríguez, Francisco J. Deive * Department of Chemical Engineering, University of Vigo, 36310, Vigo, Spain * Corresponding author: Tel.: +34986818723; E-mail address: deive@uvigo.es

Are ionic liquids extremophiles cell wall breakers? Esther Gutiérrez, M. Ángeles Sanromán, Ana Rodríguez, Francisco J. Deive * Department of Chemical Engineering, University of Vigo, 36310, Vigo, Spain * Corresponding author: Tel.: +34986818723; E-mail address: deive@uvigo.es

An analytical expression for the vapor pressure of ionic liquids based on an equation of state

An analytical expression for the vapor pressure of ionic liquids based on the Peng–Robinson equation of state is proposed. The method uses the concept of zero-pressure fugacity previously presented in the literature and that has been found to work well in the range of low vapor pressures (lower than 0.1Pa), where the values of vapor pressure of ionic liquids, up to moderate temperatures, are found. The parameters of the equation of state are generalized in terms of ionic liquid properties and results are compared with experimental data, showing average absolute deviations below 8%. The advantage of the proposed analytical expression is its solid thermodynamic foundation, the generalization of the model parameters, and its acceptable accuracy for engineering calculations.

Determination of mutual solubilities of ionic liquids and water

Two simple and universal methods for determination of solubility of ionic liquids in water are introduced in this work. The first one, which utilizes negligible vapour pressure of ionic liquids, is based on controlled evaporation of water from a sample of saturated aqueous mixture. The second one utilizes the ionic character of ionic liquids and its principle consists in measurements of electrical conductivity for series of aqueous mixtures. The methods were used for determination of aqueous solubility of five ionic liquids. Namely, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide, 1-hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and ethyl-dimethyl-propylammonium bis(trifluoromethylsulfonyl)imide. The aqueous solubility data were completed by the measurement of solubility of water in the studied ionic liquids so that full-valued data on liquid–liquid equilibrium in the temperature range from 288 to 343K are reported in the article. The obtained experimental data were correlated by the NRTL equation with temperature dependent parameters.

Performance evaluation of supported ionic liquid membrane for removal of phenol

This work evaluates the performance of ionic liquid in supported liquid membrane (SLM) for the removal of phenol from wastewater. Ionic liquids are organic salts entirely composed of organic cations and either organic or inorganic anions. Due to the fact that the vapor pressure of ionic liquid is not detectable and they are sparingly soluble in most conventional solvents, they can be applied in SLM as the organic phase. In this work, 1- n-alkyl-3-methylimidazolium salts, [C n MIM] +[X] − have been investigated so as to determine an optimal supported ionic liquid membrane. The effect of operational parameters such as pH, stirring speed and the concentration of stripping agent has been studied, and an evaluation of different membrane supports were also carried out. With a minimal amount of the ionic liquid 1-Butyl-3-methylimidazolium hydrogensulfate, 85% phenol removal could be achieved by using polytetrafluoroethylene hydrophobic membrane filter in the SLM.