Trioctylmethylammonium Bis Research Articles

Synthesis, thermal properties, vibrational spectra and computational studies of Trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ionic liquid

In this work, Aliquat 336 ([Aliquat+]) based ionic liquids containing the fluorinated anion bis(trifluoromethylsulfonyl)imide [NTf2−] was successfully prepared by the anionic exchange replacement of the chloride anion. The reaction of lithium bis(trifluoromethylsulfonyl)imide with N-Methyl-N,N,N-trioctylammonium chloride ([N1,8,8,8][Cl] in water lead to the corresponding IL, namely ([Aliquat+][NTf2−]). The obtained ionic liquid was characterized by using infrared and Raman spectra and its structure was confirmed by 1H NMR, 13C NMR, and 19F-NMR. The thermal properties were investigated by two complementary thermal analysis techniques: TGA and DTA. A hexadentate coordination mode between cation-anion was predicted by atoms in molecules (AIM) studies for the [Aliquat+][NTf2−] IL by using B3LYP/6–31G* calculations where three O atoms of the anion in Cis conformation are linked to six H atoms of cation by S-O•••H interactions. Changes in the bond orders of S and O atoms of the cation supported such observations. The predicted cation-anion distances were in the range 2.30–2.60 Å. The harmonic force fields of cation and anion were calculated and the complete assignments were performed for both species while the most important bands observed in the infrared and Raman spectra of the IL were assigned. In addition, the scaled force constants of cation and anion of the IL were also reported.

How Viscous Is the Solidlike Structure at the Interface of Ionic Liquids? A Study Using Total Internal Reflection Fluorescence Spectroscopy with a Fluorescent Molecular Probe Sensitive to High Viscosity.

Aiming at the evaluation of the viscosity of the interfacial solidlike structure of ionic liquids (ILs), we performed total internal reflection fluorescence (TIRF) spectroscopy for N,N-diethyl-N'-phenyl-rhodamine (Ph-DER), a fluorescent probe that is sensitive to viscosity in a high-viscosity range. TIRF spectra at the glass interface of trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide (TOMAC4C4N), a hydrophobic IL, showed that the fluorescence intensity of Ph-DER increases with the decrease of the evanescence penetration depth, suggesting that there exists a high-viscosity region at the interface. In contrast, glycerol, which is a molecular liquid with a bulk viscosity similar to that of TOMAC4C4N, did not show such a fluorescence increase, supporting that the formation of a highly viscous solidlike structure at the interface is intrinsic to ILs. A model analysis suggested that the high viscous region at the glass interface of TOMAC4C4N is at least twice thicker than the ionic multilayers at the air interface, implying that the solid substrate enhances the ordering of the interfacial structure of ILs. The viscosity at the glass interface of TOMAC4C4N was found to be at least 40 times higher than that of the liquid bulk.

Selective liquid-liquid extraction of molybdenum (VI) and rhenium (VII) from a synthetic pregnant leach solution: Comparison between extractants and diluents

A study on the selective solvent extraction (SX) of Molybdenum (Mo) and Rhenium (Re) from a synthetic pregnant leach solution (PLS) has been carried out using two diluents: kerosene and the ionic liquid (IL) 1-octyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide ([omim][Tf2N]) and two extractants: di(ethylhexyl)phosphoric acid (D2EHPA) and the IL trioctylmethylammonium bis(2-ethylhexyl) phosphinate [TOMA][D2EHP].It can be concluded that the D2EHPA extractant in kerosene achieved selective Mo-Re extractions, times was achieved when replacing kerosene with [omim][Tf2N], but this time with low extraction percentages.This work shows how ionic liquids, as extractants or diluents, can improve the selective separations in industrial metal extractions.

Electrochemical surface plasmon resonance as a probe of redox reactions at the ionic liquid|gold interface

Electrochemical surface plasmon resonance (ESPR) has been employed as a probe of redox reactions at the interface between gold (Au) and ionic liquid (IL). Two redox couples, ferrocene (Fc)/Fc+ and (ferrocenylmethyl)trimethylammonium (FTA+)/FTA2+, and two ILs, trioctylmethylammonium bis(trifluoromethanesulfonyl)amide ([TOMA+][C1C1N−]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim+][C1C1N−]) have been studied. In the ESPR measurements, the shift of the SPR angle has been recorded simultaneously with cyclic voltammogram (CV). It has been revealed that the SPR angle shift reproduces CV when the former is semi-differentiated or the latter is semi-integrated, and, therefore, that the ESPR response probes the surface concentration of redox couples at the IL|Au interface. Among the four combination of the two redox couples and the two ILs, the case for Fc/Fc+ in [TOMA+][C1C1N−] shows significantly greater ESPR response than the other three cases. A model has been established for the relationship between the SPR angle shift and the surface concentration of redox species. The model predicts that the SPR angle shift becomes pronounced with increasing DR/DO, the diffusion coefficient ratio of the reduced (R) and oxidized (O) species when the reduced species is initially dissolved in the IL as is the case for the present study. Significantly greater DR/DO for Fc/Fc+ in [TOMA+][C1C1N−] than the three other cases has been confirmed from the DR and DO measurements by CV with a microdisk electrode. The trend of the measured DR and DO values agrees with recent findings by researchers that small neutral solutes in ILs composed of large ions diffuse fast beyond the prediction of the Stokes-Einstein relation.

Task-Specific Ionic Liquids as Extractants for the Solvent Extraction of Molybdenum(VI) from Aqueous Solution Using Different Commercial Ionic Liquids as Diluents

In this work, the recovery of molybdenum(VI) (Mo) from aqueous solutions was carried out by solvent extraction (SX) using ammonium and phosphonium-based task-specific ionic liquids (TSILs) as extractants diluted in kerosene and two other hydrophobic room-temperature ionic liquids (RTILs). Four different TSILs were used as extractants: trioctylmethylammonium bis(2-ethylhexyl) phosphate [TOMA][D2EHP]; trioctylmethylammonium benzoate [TOMA][BA]; trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate [P6,6,6,14][D2EHP]; and trihexyltetradecylphosphonium benzoate [P6,6,6,14][BA]. These TSILs were synthesized to assess the effect of the cation and anion on the SX of Mo(VI). Experimental results indicated that high extraction percentages of Mo(VI) were obtained with all the synthesized TSILs. Besides that, the best cation was [TOMA]+ for all the diluents and [BA]− was the best anion when kerosene and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [omim][Tf2N], were the diluents. Furthermore, t...

A Binary Mixture of Ionic Liquids as a New Approach for an Experimental Diffusion Correction in the Study of Activated Processes.

A binary system of two ionic liquids, 1-ethyl-3-methylimidazolium and trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2 ] and [OMA][NTf2 ], respectively), with varying molar fractions, is introduced. It allows the dynamic viscosity to remain constant over a range of almost 60 K; this means that any activated process can be studied independent of the temperature dependence of viscosity itself. This principle is proven upon reinvestigation of electron self-exchange kinetics of tetrathiafulvalene by continuous-wave ESR line-broadening experiments. From these results, it is also confirmed that this process is totally diffusion controlled.

Recovery of Nd and Pr from NdFeB magnet leachates with bi-functional ionic liquids based on Aliquat 336 and Cyanex 272

The separation of neodymium and praseodymium was carried out from a chloride solution containing the similar composition of NdFeB magnet leach liquor. A comparative study between extractants demonstrated that the extraction efficiency of bi-functional ionic liquids (Bif-ILs) tri octylmethylammonium bis(2,4,4-trimethylpentyl)phosphate (R4NCy) and trioctylmethylammonium di(2-ethylhexyl)phosphate (R4ND) was higher than the conventional extractants such as tri-octyl methyl ammonium chloride (Aliquat 336), bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) and di-2-ethylhexyl phosphoric acid (D2EHPA) under same experimental condition. The extraction efficiency of different extractants for Nd and Pr was in the order: R4NCy>R4ND>Cyanex 272>D2EHPA>Aliquat-336. As the extraction of Nd and Pr was maximum with R4NCy Bif-ILs, the McCabe-Thiele diagram was constructed with R4NCy which showed 2 stages at 1:1 phase ratio. A 2-stage counter current simulation study showed 98.97% Nd and 99.02% Pr extraction. The loaded organic phase was stripped with H2SO4 acid and the stripping efficiencies for Nd and Pr were 98.11% and 98.75%, respectively. The extracted species was found to beMCl3⋅3R4NCy. The thermodynamic parameters were also determined for extraction of Nd and Pr with ionic liquid.

Ionic Liquid|Water Interface As an Electrochemical Reaction Field for the Formation of Novel Metal Nanostructure

Electrochemistry at interface between two immiscible electrolyte solutions (ITIES) has been explored in the novel liquid-liquid two-phase system of water (W) and ionic liquids (ILs) since more than a decade ago [1,2]. One of several characteristics of ILs is the ability to disperse and stabilize metal nanostructures in ILs without addition of any capping reagents, which seems to result from the existence of ionic multilayers [3,4], a rigid interfacial structure, formed on the metal surface. This characteristic motivated us to study electrochemical deposition of metal at the IL|W interface utilizing electron transfer across the interface. When we used AuCl4 - as the metal source dissolved in W and a reducing reagent dissolved in trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, which is a highly hydrophobic IL, spontaneous and simultaneous electron transfer-ion transfer reaction occurred and dendritic Au nanofibers were formed at the interface [5]. Similar dendritic nanofibers were formed at the IL|W interface of other highly hydrophobic ILs, although the fiber diameter depended on the ionic species of the ILs. On the other hand, when we used a conventional organic solvent, dichloromethane, instead of ILs, we obtained not nanofibers but micro-scale burr-like structures. In the present paper, the mechanism of the formation of such highly anisotropic nanostructure will be discussed and the application of this system to other nanostructures such as metal-polymer composites will be introduced. [1] T. Kakiuchi and N. Nishi, Electrochemistry, 74 (2006) 942-948. [2] Z. Samec, J. Langmaier, T. Kakiuchi, Pure Appl. Chem., 81 (2009) 1473-1488. [3] N. Nishi, Y. Yasui, T. Uruga, H. Tanida, T. Yamada, S. Nakayama, H. Matsuoka, T. Kakiuchi, J. Chem. Phys., 132 (2010) 164705(1-6). [4] N. Nishi, T. Uruga, H. Tanida, J. Electroanal. Chem., 759 (2015) 129-136. [5] N. Nishi, T. Kakinami, T. Sakka, Chem. Commun., 51 (2015) 13638-13641.

Solvent extraction of plutonium(IV) in monoamide – ammonium ionic liquid mixture

Abstract The extraction behavior of plutonium(IV) was studied in the room temperature ionic liquid, trioctylmethylammonium bis(trifluoromethanesulfonyl)imide ([N 1888 ][NTf 2 ]) containing a monoamide, N,N- dihexyloctanamide (DHOA). The unusual extraction of Pu(IV) observed in this ionic liquid system was reported in this paper. The extraction behavior of plutonium(IV) was investigated as a function of various parameters, such as feed acid concentration, extractant and ionic liquid concentration, type of the extractants, equilibration time and temperature. Changing the extractant from DHOA to tri- n -butyl phosphate reduced the distribution ratio of Pu(IV). The extraction trend of Pu(IV) in neat [N 1888 ][NTf 2 ] was compared with those observed in other ionic liquids such as 1-alkyl-3-methylimidazolium bistriflimide ([C n mim][NTf 2 ]). Pu(IV) extraction in [N 1888 ][NTf 2 ] was found to follow a combination of anion exchange mechanism and neutral solvation pathway at feed acidities above 2 M HNO 3 . The extraction of Pu(IV) in DHOA/[N 1888 ][NTf 2 ] was also compared with those observed in a molecular diluent system, DHOA/ n -DD. All thermodynamic parameters governing the extraction of plutonium(IV) in [N 1888 ][NTf 2 ] was determined and discussed in detail. Stripping of Pu(IV) from the loaded ionic liquid phase was performed using dilute nitric acid.

Evaluation of ionic liquids as dispersed phase during the production of lactones with E. coli in a three phase partitioning bioreactor

The aim of this work was to experimentally and theoretically evaluate the performance of four ionic liquids (ILs) used in the three-phase (air–water–IL) partitioning bioreactor (TPPB) for the production of bicyclic lactone (1S,5R)-2-oxabicyclo[3.3.0]oct-6-en-3-one from bicyclic ketone bicyclo[3.2.0]hept-2-en-6-one over Escherichia coli strain TOP10 pQR239. In particular, partition coefficients of the substrate and product, mass-transfer coefficients of the substrate, product and oxygen, as well as the deactivation parameters related to the loss of cell viability, owing to the presence of the IL, were determined. To the best of our knowledge, cell viability was described, for the first time, using a power law equation model. The operation of the biphasic system without inhibitory conditions led to a substrate conversion of 100%, whereas the conversion was approximately 25% under inhibitory conditions. Besides, when the IL was used as the dispersed phase in the TPPB, the substrate conversion under inhibitory conditions was between 20% and 85%. All evaluated ILs were thermodynamically suitable for use as the dispersed phase; however, all of them provoked a loss in cell viability. When trioctylmethylammonium bis (trifluoromethylsulfonyl)imide [OMA][BTA] was used in the three-phase system, the highest substrate conversion (ca. 85%) and the lowest loss of cell viability (ca. 55%) were observed, even though this IL presented lower partition coefficients for the substrate and product as well as the lowest oxygen, substrate and product mass-transfer coefficients compared to the other ILs under the studied operating conditions. These results indicate that the effect of the IL on the cell viability is an essential parameter that must be considered before the application of an IL in TPPB technology.

Mathematical model of a three phase partitioning bioreactor for conversion of ketones using whole cells

Abstract In this study we developed a pseudo heterogeneous mathematical model for the oxidation of bicyclic ketone bicyclo[3.2.0]hept-2-to-6-one to bicyclic lactone (1S,5R)-(-)-2-oxabiciclo[3.3.0]oct-6-en-3-ona using whole cells of E. coli strain TOP10 pQR239 in a three-phase partitioning bioreactor (TPPB). The pseudo heterogeneous TPPB model accounted for mass transfer mechanisms occurring in the air–water and water–ionic liquid phases along with bioconversion and loss of cell viability caused by ionic liquid – trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ([OMA][BTA]). The development of the model was based on reactor engineering principles and, hence, experiments with and without bioconversion were carried out in order to characterize thermodynamic ( K ps and K pp ), transport ( k s , k p and A ) and kinetic ( k i and k i ′ ) parameters along with the loss of cell viability ( k in ) parameter for the mechanisms involved. The model described adequately the bioconversion of experimental data with two different ionic liquid fractions, namely 5% (v/v) and 12.5% (v/v). A parametric sensitivity analysis of the model was conducted to obtain information on the effect of oxygen transport rate on bioconversion. The development of the TPPB model led to the following findings: (i) 5% (v/v) ionic liquid fraction caused less cell deactivation; (ii) presence of ionic liquid decreased the oxygen transport rate; and (iii) a higher oxygen transport rate lead to a higher bioconversion but also cell inactivation.

Highlighting a Solid-Like Behavior in RTILs: Tri-octylmethylammonium Bis(trifluoromethanesulfonyl)imide TOMA-TFSI

Careful measurements of the dynamic response of the room -temperature ionic liquid (RTIL) trioctylmethylammonium bis(trifluoromethanesulfonyl)imide reveal that it exhibits actually a (low-frequency) solid-like response when solicited at the submillimeter scale with a low shear strain. The solid-like response is measured away from the glass transition (at around 100 °C above Tg), ruling out reminiscent transitional effects but suggesting that the dynamic properties of the RTIL are governed by long-range elastic intermolecular interactions.

Developing microwave-assisted ionic liquid microextraction for the detection and tracking of hydrophobic pesticides in complex environmental matrices

In the present study, we have developed a novel dispersive liquid–liquid microextraction (DLLME) based on microwave-assisted DLLME (MADLLME) using ionic liquids for the separation of environmentally-relevant pyrethroid pesticides from various aqueous milieux. High-performance liquid chromatography (HPLC) was employed for the detection and quantitative tracking of the pesticides. Six different ILs were preliminarily tested as extraction solvents against four representative model pyrethroids. The optimization of the current method was derived by consideration of the dispersal solvent, ionic liquid choice, extraction container material, aqueous-phase pH, and microwave conditions (particularly, the applied power and irradiation time). Optimal results were achieved using methanol as a dispersal solvent with trioctylmethylammonium bis(trifluoromethylsulfonyl)imide ([N8881][Tf2N]) as the extraction solvent at a microwave power of 200 W for 60 s. A number of spiked food samples (e.g., honey, milk, assorted fruits) were also tested using MADLLME, with excellent recoveries achieved from these complex matrices as compared to DLLME alone.

Surface Structure of a Hydrophobic Ionic Liquid Probed by Spectroscopic Ellipsometry

The surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl) amide ([TOMA+][C4C4N–]) has been studied using spectroscopic ellipsometry at 300 K. The values for delta, which is the phase difference between p-polarized and s-polarized reflection coefficients, deviate from zero to positive values, suggesting that spectroscopic ellipsometry detects surface structures such as surface roughness and surface layers at the [TOMA+][C4C4N–] surface. A model taking into account not only the surface roughness estimated using the capillary wave theory but also ionic multilayers, which was found to exist at the [TOMA+][C4C4N–] surface by a recent X-ray reflectivity study, well reproduces the experimental delta values. Spectroscopic ellipsometry is demonstrated to be a complementary technique to X-ray reflectometry to detect surface structures at ionic liquid interfaces.

Mass transfer coefficient determination in three biphasic systems (water–ionic liquid) using a modified Lewis cell

Baeyer–Villiger bioconversion productivity of the cyclic ketone (±)-cis-bicyclo [3.2.0] hept-2-en-6-ona by the biocatalyst Escherichia coli TOP10 pQR239 in a multiphase system can be limited by mass transport. Mass transfer rates through the liquid–liquid interface depend on the volumetric mass transfer coefficient (kA) and the substrate and product partition coefficients. In situ experimental determination of the volumetric mass transfer coefficient in a partitioning bioreactor is complex. In this work, the substrate (kS) and product (kP) global mass transfer coefficients were determined in a modified Lewis cell in three water–ionic liquids systems. The ionic liquids used were butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide [MeBuPyrr][BTA], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][BTA] and 1-butyl-3-metyl-imidazolium hexafluorophosphate [BMIM][PF6]. The maximum kS and kP values obtained were 4.35×10−5 and 1.21×10−5ms−1 for water-[MeBuPyrr][BTA] system; 1.53×10−5 and 7.84×10−6ms−1 for water-[OMA][BTA] system, respectively; and kS values up to 1.01×10−5ms−1 were found for the water-[BMIM][PF6] system. The association among the mass transfer coefficients and the physicochemical properties (interfacial tension, viscosity and density) and the thermodynamics (partition coefficients) are analysed and discussed. Finally, the volumetric mass transfer coefficients (kSA and kPA) were calculated using interfacial areas (A) of the dispersed ionic liquid phase estimated from the “Sauter” mean drop diameter (d32) in a one litre stirred tank partitioning bioreactor.

Charging current probing of the slow relaxation of the ionic liquid double layer at the Pt electrode

Abstract The slow relaxation of the electrical double layer on the ionic liquid (IL) side of the electrified interface, which was recently found at the IL|water interface, is detected voltammetrically also at a polycrystalline Pt electrode in two ionic liquids, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA + ][C 4 C 4 N − ]) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C 2 mim + ][C 1 C 1 N − ]). The potential-step transients at the Pt electrode show exponential decays, in which the slower relaxation time is on the order of 0.1–0.4 s in both [TOMA + ][C 4 C 4 N − ] and [C 2 mim + ][C 1 C 1 N − ]. The slow relaxation commonly seen at the Pt electrode in highly viscous [TOMA + ][C 4 C 4 N − ] (2.0 Pa s) and much less viscous [C 2 mim + ][C 1 C 1 N − ] (0.0325 Pa s), which was also seen at the IL|water interface, suggests the presence of a common origin of the slow relaxation on the ionic liquid side of the electrified interface, possibly the slow rearrangement of ions in the electrical double layer that consists of an ionic liquid. An even slower mode of the relaxation was detected in cyclic voltammograms as the time-dependent double layer capacitance.

Differential pulse stripping voltammetry of moderately hydrophobic ions based on hydrophobic ionic liquid membranes supported on the Ag/AgCl electrode

Differential pulse stripping voltammetry (DPSV) based on the ion transfer across the hydrophobic ionic liquid and an aqueous sample solution has been achieved for the analysis of moderately hydrophobic ions. The ionic liquid membrane was made of the double layers of gelled trioctylmethylammonium bis(nona-fluorobutanesulfonyl)amide ([TOMA +][C 4C 4N −]), a hydrophobic ionic liquid. The first [TOMA +][C 4C 4N −] layer containing trioctylmethylammonium chloride (TOMACl) was in contact with a AgCl layer of a planar Ag/AgCl electrode, and the second [TOMA +][C 4C 4N −] layer without containing TOMACl was in contact with a sample solution. The linearity between the DPSV peak and the concentration of analytes, tetrapropylammonium and tridecafluoroheptanoate, was found between 5 μmol dm −3 and 200 μmol dm −3 of these ions.

Voltammetric Manifestation of the Ultraslow Dynamics at the Interface between Water and an Ionic Liquid

The ultraslow relaxation (on the order of minutes) of the electrical double-layer structure, related to a change in the phase-boundary potential across the interface between water (W) and the ionic liquid (IL) trioctylmethylammonium bis(nonafluorobutanesufonyl)amide ([TOMA(+)][C(4)C(4)N(-)]) (Y. Yasui et al., J. Phys. Chem. B. 2009, 113, 3273), appears to be invisible in the transfer of tetrapropylammonium ions across the [TOMA(+)][C(4)C(4)N(-)]|W interface, provided that the charging current, which shows an unusual dependence on the voltage scan rate, is subtracted to obtain the faradaic current. This counterintuitive observation can be explained by the differences in the timescales of the fast and slow components of the relaxation dynamics of the electrical double layer on the IL side (ms and min). In contrast, the effect of the slow dynamics becomes surfaced in ion-transfer voltammetry when the ion is surface-active. The transfer of pentadecafluorooctanoate across the [TOMA(+)][C(4)C(4)N(-)]|W interface is irreversible, which is attributable to the self-inhibition of pentadecafluorooctanoate ions transferred to the IL phase. This process is likely to be affected by the ultraslow structural change of the IL side of the interface.

A comparison of the ultraslow relaxation processes at the ionic liquid|water interface for three hydrophobic ionic liquids

The ultraslow relaxation, on the order of a few seconds or longer, of the structure of the electrical double layer in response to the change in the phase-boundary potential across the ionic liquid (IL)|water(W) interface, which was recently reported for trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, has been confirmed in two new hydrophobic ionic liquids, trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide and trihexyltetradecylphosphonium tetrakis(pentafluorophenyl)borate. A comparison of the degree of the hysteresis in electrocapillary curves for these ILs with those for trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide demonstrates that the degree of the hysteresis is not correlated with the viscosity of these ILs. The ultraslow relaxation of the electrical double layer seems to be a general feature of ILs at electrified interfaces.

Electrocapillarity under Ultraslow Relaxation of the Ionic Liquid Double Layer at the Interface between Trioctylmethylammonium Bis(nonafluorobutanesulfonyl)amide and Water

Electrocapillarity has been studied in detail at the interface between a hydrophobic ionic liquid (IL), trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, and water, where the ultraslow relaxation of the structure of the electrical double layer on the IL side of the interface exists. The response of the interfacial tension and that of the charging current to the potential step can be fitted by a double exponential model having the relaxation time constants of a few seconds and 100 s. The hysteresis in the interfacial tension in the IL diluted with nitrobenzene persists even in an almost 1:1 mixture of the IL and nitrobenzene. The thermodynamically definable double layer capacitance (C(dl)) estimated from the equilibrated electrocapillary curve, that is, the interfacial tension versus potential curve, at the IL|water interface has a maximum value of about 60 microF cm(-2) in the vicinity of the potential of zero charge (pzc) when the aqueous phase is 0.1 mol dm(-3) LiCl. The C(dl) versus the potential plot shows a characteristic camelback shape, showing a shallow minimum at the pzc, where the C(dl) value is 42 microF cm(-2). This minimum seems to reflect the contribution of C(dl) on the aqueous side of the interface to the total capacitance.