Determination of the physical properties of room temperature ionic liquids using a Love wave device

In this work, we have shown that a 100 MHz Love wave device can be used to determine whether room temperature ionic liquids (RTILs) are Newtonian fluids and have developed a technique that allows the determination of the density-viscosity product, ρη, of a Newtonian RTIL. In addition, a test for a Newtonian response was established by relating the phase change to insertion loss change. Five concentrations of a water-miscible RTIL and seven pure RTILs were measured. The changes in phase and insertion loss were found to vary linearly with the square root of the density-viscosity product for values up to (ρη)(1/2) ~ 10 kg m(-2) s(-1/2). The square root of the density-viscosity product was deduced from the changes in either phase or insertion loss using glycerol as a calibration liquid. In both cases, the deduced values of ρη agree well with those measured using viscosity and density meters. Miniaturization of the device, beyond that achievable with the lower-frequency quartz crystal microbalance approach, to measure smaller volumes is possible. The ability to fabricate Love wave and other surface acoustic wave sensors using planar metallization technologies gives potential for future integration into lab-on-a-chip analytical systems for characterizing ionic liquids.     

Responses of a Quartz Crystal Resonator Against Viscosity of Liquid up to 700 MPa

Conductance spectra of a quartz crystal resonator against sweep frequency were obtained in methanol and 1-pentanol up to 700 MPa using a piston-cylinder type cell. A resonance peak around a nominal frequency was observed on the conductance spectra. The frequency shift of the resonance peak increased linearly with pressure. The frequency shift against pressure was represented as the sum of the parts attributed to the viscosity of the liquid and that on the pressure effect of the resonator. The measurements for the resonator immersed in methanol and 1-propanol showed that the part attributed to the compression of the resonator on the frequency shift was similar for the two liquids. An empirical relation was developed on the electrical response of the resonance against the viscosity of the surrounding liquid up to 700 MPa based on these results. It may become possible to estimate the viscosity-density product of various liquids up to this pressure from the frequency shift.     

Electroanalytical determination of trace chloride in room-temperature ionic liquids

The electroanalytical quantification of chloride in [C4mim][BF4], [C4mim][NTf2], and [C4mim][PF6] ionic liquids has been explored using linear sweep and square wave voltammetry. Cathodic stripping voltammetry at a silver disk electrode is found to be the most sensitive. The methodology is based on first holding the potential of the electrode at +2.0 V (vs Ag wire), to accumulate silver chloride at the electrode. On applying a cathodic scan, a stripping wave is observed corresponding to the reduction of the silver chloride. This stripping protocol was found to detect ppb levels of chloride in [C4mim][BF4], [C4mim][NTf2], and [C4mim][PF6]. Although other methods for chloride have been reported for [BF4](-)- and [PF6](-)-based ionic liquids, no methods have been reported for [NTf2](-) ionic liquids.     

[C_4mim][BF_4]粘度的模拟与实验

为了研究离子液体的粘度特性,以1-丁基-3-甲基咪唑四氟硼酸盐([C4mim][BF4])离子液体为研究对象进行模拟计算与实验测试.基于分子动力学原理,编译了离子液体粘度的模拟计算程序,对[C4mim][BF4]离子液体完成了粘度模拟计算.搭建了粘度测试系统,进行离子液体的粘度测试.通过实验数据与模拟数据的对比,验证了模拟结果的准确性.另外,根据模拟粘度值的拟合曲线,分析了离子液体粘度的变化规律.同时,通过与水粘度的比对研究,阐述了[C4mim][BF4]离子液体的粘度特点.     

Ionic liquids: a new class of sensing materials for detection of organic vapors based on the use of a quartz crystal microbalance

A QCM device employing ionic liquids as the sensing materials for organic vapors has been developed and evaluated. The sensing mechanism is based on the fact that the viscosity of the ionic liquid membrane decreases rapidly due to solubilization of analytes in the ionic liquids. This change in viscosity, which varies with the chemical species of the vapors and the types of ionic liquids, results in a frequency shift of the corresponding quartz crystal. The QCM sensor demonstrated a rapid response (average response time of less than 2 s) to organic vapors with an excellent reversibility because of the fast diffusion of analytes in ionic liquids. Furthermore, the ionic liquids, with zero vapor pressure and stable chemical properties, ensure a long-term shelf life for the sensor.     

Viscosity sensor utilizing a piezoelectric thickness shear sandwich resonator

This paper describes a novel quartz crystal sensor for measurement of the density-viscosity product of Newtonian liquids. The sensor element consists of two piano-convex AT-cut quartz crystals vibrating in a thickness-shear mode with the liquid sample in between. This special set-up allows suppression of disturbing resonances in the liquid layer. Such resonances are generated in the common single-plate arrangements due to compressional waves caused by spurious out-of-plane displacements of the shear vibrating finite plate. The primary measurands of the sensor are the fundamental resonance frequency and the associated resonance Q-value, which are influenced by the viscously entrained liquid contacting the quartz surface. The sensor allows the measurement of samples with viscosities from almost zero (air!) up to 200 cP with a sample volume of 130 mul.     

Conditions required to achieve the apparent equivalence of adhered solid- and solution-phase voltammetry for ferrocene and other redox-active solids in ionic liquids

The voltammetry of ferrocene (Fc) and Fc+ in the room-temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM x PF6) has been studied when solid is adhered to glassy carbon or platinum disk electrodes. Due to the slow dissolution kinetics and small diffusion coefficients in the viscous BMIM x PF6 ionic liquid, it is possible to obtain voltammograms of adhered Fc or Fc+ solid that are essentially indistinguishable (except for the current magnitude) from the reversible solution-phase Fc(0/+) process widely employed to provide a reference potential scale. However, the nature of the voltammetry obtained from the adhered solid is governed by the thickness (mass of the solid) of the particle layer. The mechanism proposed to explain the equivalence to solution-phase data involves dissolution at the particle/ionic liquid interface and is supported by electrochemical quartz microbalance measurements and a numerical simulation. Extensive studies on other redox-active solids suggest that voltammograms of solid particles adhered to the electrode surface in contact with ionic liquids frequently exhibit classical behavior associated with solution-phase diffusion-controlled voltammetry. Consequently, the method of adhering microparticles onto an electrode surface can frequently provide an efficient method of establishing ionic liquid solution-phase redox data using extremely small quantities of solid.     

AGET ATRP of acrylonitrile with ionic liquids as reaction medium without any additional ligand

Atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) was carried out for the first time in 1-methylimidazolium acetate ([mim][AT]), 1-methylimidazolium propionate([mim][PT]), and 1-methylimidazolium butyrate ([mim][BT]), respectively. The polymerization was approached by using ascorbic acid (VC) as a reducing agent, ethyl 2-bromoisobutyrate (EBiB) as initiator, only FeBr₃ as catalyst without any additional ligand. Kinetic studies showed that both AGET ATRP of AN in the absence of oxygen and in the presence of air proceeded in a well-controlled manner. Under the same conditions, the polymerization in the presence of air provided rather slower reaction rate and showed better control of molecular weight and its distribution than in the absence of oxygen. The sequence of the apparent polymerization rate constants of AGET ATRP of AN in three ionic liquids was k_app([mim][AT]) > k_app([mim][PT]) > k_app([mim][BT]). The living nature of the polymerization was confirmed by chain end analysis and block copolymerization of methyl methacrylate with polyacrylonitrile as macroinitiator. All the three ionic liquids and FeBr₃ could be recycled and reused and had no effect on the living nature of polymerization.     

Examination of ionic liquids and their interaction with molecules, when used as stationary phases in gas chromatography.

Stable room-temperature ionic liquids (RTILs) have been used as novel reaction solvents. They can solubilize complex polar molecules such as cyclodextrins and glycopeptides. Their wetting ability and viscosity allow them to be coated onto fused silica capillaries. Thus, 1-butyl-3-methylimidazolium hexafluorophosphate and the analogous chloride salt can be used as stationary phases for gas chromatography (GC). Using inverse GC, one can examine the nature of these ionic liquids via their interactions with a variety of compounds. The Rohrschneider-McReynolds constants were determined for both ionic liquids and a popular commercial polysiloxane stationary phase. Ionic liquid stationary phases seem to have a dual nature. They appear to act as a low-polarity stationary phase to nonpolar compounds. However, molecules with strong proton donor groups, in particular, are tenaciously retained. The nature of the anion can have a significant effect on both the solubilizing ability and the selectivity of ionic liquid stationary phases. It appears that the unusual properties of ionic liquids could make them beneficial in many areas of separation science.     

Multifunctional role of an ionic liquid in melt-blended poly(methyl methacrylate)/ multi-walled carbon nanotube nanocomposites

Poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotube (MWNT) nanocomposites with a homogeneous dispersion of MWNTs have been fabricated by a simple melt-mixing method in the presence of a room-temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]. It has been found that the ionic liquid provided multiple functions in the preparation of the nanocomposites: (1)?the ionic liquid acts as an effective compatibilizer to significantly improve the dispersion of MWNTs in the PMMA matrix; (2)?the ionic liquid is an efficient plasticizer for the prepared nanocomposites, inducing a drastically reduced glass transition temperature in the PMMA matrix; (3)?the ionic liquid acts as a processing aid for the melt processing of PMMA/MWNT nanocomposites; (4)?the ionic liquid increases the electrical conductivity as a dopant. This strategy is free of solvents and compatible with industrial applications, which opens new avenues for the larger-scale fabrication of polymer/carbon nanotube nanocomposites.     

Use of 1-alkyl-3-methylimidazolium l-lactates as both ligand and reaction media for AGET ATRP of acrylonitrile

Chiral ionic liquids, [C₂mim][LLA], [C₄mim][LLA] and [C₆mim][LLA] were firstly applied as both ligand and reaction media for atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) with ascorbic acid (VC) as reducing agent in the presence of air. A small but clear increase of polyacrylonitrile (PAN) isotacticity was observed for AGET ATRP of AN in [C₆mim][LLA] than in [C₆mim][BF₄]. PAN isotacticity markedly increased with the content of [C₆mim][LLA]. Compared with in [C₂mim][LLA] and [C₄mim][LLA], the rate of AGET ATRP of AN in [C₆mim][LLA] was fastest and the polymerization was best controlled. Well-defined PAN with molecular weight at 76,590, relatively narrower distribution at 1.27 and higher isotacticity at 0.37 was successfully prepared in [C₆mim][LLA].     

Determination of water in room temperature ionic liquids by cathodic stripping voltammetry at a gold electrode

An electrochemical method based on cathodic stripping voltammetry at a gold electrode has been developed for the determination of water in ionic liquids. The technique has been applied to two aprotic ionic liquids, (1-butyl-3-ethylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate), and two protic ionic liquids, (bis(2-hydroxyethyl)ammonium acetate and triethylammonium acetate). When water is present in an ionic liquid, electrooxidation of a gold electrode forms gold oxides. Thus, application of an anodic potential scan or holding the potential of the electrode at a very positive value leads to accumulation of an oxide film. On applying a cathodic potential scan, a sensitive stripping peak is produced as a result of the reduction of gold oxide back to gold. The magnitude of the peak current generated from the stripping process is a function of the water concentration in an ionic liquid. The method requires no addition of reagents and can be used for the sensitive and in situ determination of water present in small volumes of ionic liquids. Importantly, the method allows the determination of water in the carboxylic acid-based ionic liquids, such as acetate-based protic ionic liquids, where the widely used Karl Fischer titration method suffering from an esterification side reaction which generates water as a side product.     

Phase Behavior of N2O and CO2 in Room-Temperature Ionic Liquids [bmim][Tf2N], [bmim][BF4], [bmim][N(CN)2], [bmim][Ac], [eam][NO3], and [bmim][SCN]

The gas solubility of nitrous oxide (N₂O) in room-temperature ionic liquids, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium thiocyanate, and ethylammonium nitrate has been measured at isothermal conditions from about (283 to 348)K using a gravimetric microbalance. The observed pressure–temperature composition (PTx) data have been analyzed by use of a generic Redlich-Kwong equation-of-state (EOS) model, which has been successfully applied in our previous works. The interaction parameters have been determined using our measured vapor–liquid equilibrium data. Vapor–liquid–liquid equilibrium measurements have been made and validate EOS model predictions which suggest that these systems demonstrate Type III and Type V phase behavior, according to the classification of van Konynenburg and Scott. The global phase behavior of N₂O has also been compared with both the measured data from this study and literature data for carbon dioxide (CO₂) in each ionic liquid and Henry’s law constants are compared at room temperature (298.15 K).     

Organic vapor sensing with ionic liquids entrapped in alumina nanopores on quartz crystal resonators

We report on a concept for vapor sensing with the quartz crystal microbalance where the vapor phase is absorbed into small droplets of an ionic liquid. The liquid is contained in the pores of a nanoporous alumina layer, created on the front electrode of the quartz crystal by anodization. Ionic liquids are attractive for vapor sensing because--being liquids--they equilibrate very fast, while at the same time having negligible vapor pressure. Containing the ionic liquids inside cylindrical cavities of a solid matrix removes all problems related to the liquid's softness as well as the possibility of dewetting and flow. The absence of viscoelastic effects is evidenced by the fact that the bandwidth of the resonance remains unchanged during the uptake of solvent vapor. The Henry constants for a number of solvents have been measured.     

Contributions of amplitude measurement in QCM sensors

The characteristics of the amplifier and the feedback loop of a quartz crystal series oscillating circuit are investigated. The fact that the change of the vibration amplitude of the quartz crystal is proportional to the change of its motional resistance is derived. The concept of a characteristic damping coefficient is introduced and the behavior of a quartz crystal vibrating in liquids is analyzed. The experiment shows that the effect of mass loading can be distinguished from that of the liquid damping of a quartz crystal microbalance (QCM) sensor in liquids by simultaneously measuring the amplitude and the frequency change     

Direct-on-barrier copper electroplating on ruthenium from the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

The "direct-on-barrier" electroplating of copper on ruthenium from a 1 mol dm⁻³ solution of CuCl in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide, [C₂mim][N(CN)₂], is reported. Continuous layers of copper with a preferential Cu(111) orientation were obtained from this electrolyte. The copper coatings were investigated by top view scanning electron microscopy (SEM), X-ray diffraction (XRD), and focused ion beam transmission electron microscopy (FIB-TEM). The nucleation density was both theoretically and experimentally evaluated by the Scharifker-Hills model and transmission electron microscopy, respectively. The direct plating of copper on resistive substrates for advanced interconnects and package is a promising new application of ionic liquids.     

A new class of magnetic fluids: bmim[FeCl/sub 4/] and nbmim[FeCl/sub 4/] ionic liquids

The responses to a magnet of two room-temperature ionic liquids containing tetrachloroferrate(III) ions, 1-butyl-3-methylimidazolium tetrachloroferrate (bmim[FeCl/sub 4/]) and 1-butyronitrile-3-methylimidazolium tetrachloroferrate (nbmim[FeCl/sub 4/]) are compared. Although their magnetic susceptibilities are similar, the observed responses are distinct from each other, suggesting that the response is determined not only by the magnetic susceptibility but also by the other factors including density, viscosity, and surface tension. The two magnetic ionic liquids constitute a new class of magnetic fluids that hold many attractive physical properties for practical applications.     

Volumetric and Isentropic Compressibility Behavior of Ionic Liquid, 1-Propyl-3-Methylimidazolium Bromide in Acetonitrile,Dimethylformamide, and Dimethylsulfoxide at <Emphasis Type="Italic">T</Emphasis> = (288.15 to 308.15) K

Density and speed-of-sound data for 1-propyl-3-methylimidazolium bromide ([C₃mim][Br]) + acetonitrile (MeCN), [C₃mim][Br] + dimethylformamide (DMF), and [C₃mim][Br] + dimethylsulfoxide (DMSO) binary mixtures in the dilute concentration region are reported at T = (288.15 to 308.15) K. From these data, apparent molar volume, isentropic compressibility, excess molar volume, and isentropic compressibility deviation values have been calculated. Negative deviations from the ideal behavior of both molar volume and isentropic compressibility have been observed for all systems investigated in this study. It has been found that deviations from ideal behavior for the [C₃mim][Br] + MeCN system are larger than those for the [C₃mim][Br] + DMF system which, in turn, are larger than those for the [C₃mim][Br] + DMSO system. The results have been interpreted in terms of ion–dipole interactions and structural factors of the ionic liquid and investigated organic solvents.     

Memory effect in an ionic liquid matrix containing single-walled carbon nanotubes and polystyrene

We report the use of an ionic liquid (IL) gel matrix containing a blend of single-walled carbon nanotubes (SWNTs) and polystyrene (PS) as a memory device. SWNTs and PS beads were mixed in a room-temperature IL, 1-butyl-3-methyl-hexafluorophosphate ([BMIM][PF(6)]). The composite gel was sandwiched between a bottom ITO glass and a top aluminium electrode. By merely changing the concentrations of SWNTs in the inert insulating PS matrix, we observed several distinct electrical properties of the device, such as an insulator, a memory in terms of switching and negative differential resistance (NDR), and a conductor. The electric bistable switching hops between a higher impedance (OFF) state and a lower impedance (ON) state which is approximately equal to five orders of current decays.     

Analysis of piezoelectric bulk-acoustic-wave resonators as detectors in viscous conductive liquids

An analytical solution for the resonance condition of a piezoelectric quartz resonator with one surface in contact with a viscous conductive liquid is presented. The characteristic equation that describes the resonance condition and accounts for all interactions including acoustoelectric interactions with ions and dipoles in the solution is obtained in terms of the crystal and liquid parameters. A simple expression for the change in the resonance frequency is obtained. For viscous nonconductive solutions, the frequency change is reduced to a relationship in terms of the liquid density and viscosity. For dilute conductive liquid, the change in frequency is derived in terms of the solution conductivity and dielectric constant. The boundary conditions for the problem are defined with and without the electrical effects of electrodes. Experiments were conducted with various viscous and conductive chemical liquids using a fabricated miniature liquid flow cell containing an AT-cut quartz crystal resonator. The results, which show good agreement with the theory, on the use of quartz crystal resonators as conductivity and/or viscosity sensors are reported.