Ultraslow relaxation of the structure at the ionic liquid|gold electrode interface to a potential step probed by electrochemical surface plasmon resonance measurements: asymmetry of the relaxation time to the potential-step direction.

The relaxation of the structure in the electrical double layer at the ionic liquid|gold interface to the steps of the electrode potential has been studied using surface plasmon resonance (SPR) measurements. The relaxation of the SPR resonance angle occurs on the order of 100 s, which is distinctively slower than the RC time constant of the cell, about 0.1 s.

Ionic liquid salt bridge with low solubility of water and stable liquid junction potential based on a mixture of a potential-determining salt and a highly hydrophobic ionic liquid.

A new type of ionic liquid salt bridge (ILSB) based on a mixture of pentyltripropylammonium bis(pentafluoroethanesulfonyl)amide, [N(3335)(+)][C(2)C(2)N(-)], and heptadecafluorodecyltrioctylphosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, [TOPH(+)][TFPB(-)], shows a stable phase-boundary potential (Δ(IL)(W)φ) between the ILSB and an aqueous solution of MCl (M = H(+), Li(+), Na(+), and K(+)) over the concentration range from 0.05 mM to 0.5 M with an averaged excursion in 1 h of ±0.

Determination of single-ion activities of H+ and Cl- in aqueous hydrochloric acid solutions by use of an ionic liquid salt bridge.

Single-ion activities of H(+) and Cl(-) in aqueous hydrochloric acid solutions up to 500 mmol·dm(-3) HCl have been determined, independently of each other, with reasonable accuracy, 95% confidence interval of log(10)γ being ±0.012 at 25 °C, by use of an ionic liquid salt bridge inserted in a Harned cell. The geometric averages of those activities agree well with the literature values of the mean ionic activity of HCl determined with a Harned cell up to an ionic strength of 500 mmol·dm(-3).

Potential-dependent adsorption and transfer of poly(diallyldialkylammonium) ions at the nitrobenzene|water interface.

Electrochemically driven adsorption and partition of a series of poly(diallyldialkylammonium) ions (PDADAA(+): alkyl = methyl, ethyl, propyl, and butyl) at the nitrobenzene (NB)|water (W) interface have been studied using voltammetry and electrocapillary measurements. When the phase-boundary potential, Δφ, that is, the inner potential of the W phase referred to that of the NB phase, is negative, poly(diallyldimethylammonium) (PDADMA(+)) shows little surface activity. The scanning of Δφ in the positive direction induces, first, the adsorption of PDADMA(+) at the interface and, then, the desorption of adsorbed PDADMA(+) ions into the NB phase, followed by the diffusion-limited transfer of PDADMA(+) from W to NB.

Temperature dependence of multilayering at the free surface of ionic liquids probed by X-ray reflectivity measurements.

The effect of the temperature on the surface layering of ionic liquids has been studied for two ionic liquids, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide([TOMA(+)][C(4)C(4)N(-)]) and trihexyltetradecylphosphonium bis(nonafluorobutanesulfonyl)amide ([THTDP(+)][C(4)C(4)N(-)]), using X-ray reflectivity measurements at 285, 300, and 315 K. Both [TOMA(+)][C(4)C(4)N(-)] and [THTDP(+)][C(4)C(4)N(-)] develop multilayers at the surface. The structure of the multilayers at the [TOMA(+)][C(4)C(4)N(-)] surface shows little temperature-dependent change, whereas that at the [THTDP(+)][C(4)C(4)N(-)] surface clearly becomes diffused with increasing temperature.

Determination of the activity of hydrogen ions in dilute sulfuric acids by use of an ionic liquid salt bridge sandwiched by two hydrogen electrodes.

The activities of hydrogen ions in 20-200 μmol dm(-3) H(2)SO(4) solution were estimated by use of an ionic liquid salt bridge (ILSB), made of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide (TBMOEPC(2)C(2)N), sandwiched by two hydrogen electrodes. The experimental pH values (pH = -log a(H), where a(H) is the activity of hydrogen ions) were in good agreement, within 0.01 pH unit, with those calculated using the Pitzer model.

Ionic liquid salt bridge based on tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide for stable liquid junction potentials in highly diluted aqueous electrolyte solutions.

A moderately hydrophobic ionic liquid, tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide ([TBMOEP(+)][C(2)C(2)N(-)]), shows a very stable liquid junction potential upon contact with an aqueous solution whose ionic strength is as low as 1 μ mol dm(-3). The stability with the maximum excursion of the potential within ± 0.5 mV for 30 min is very promising for accurate determination of pH and other single ion activities potentiometrically.

Stability of a Ag/AgCl reference electrode equipped with an ionic liquid salt bridge composed of 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)-amide in potentiometry of pH standard buffers.

The stability of a Ag/AgCl reference electrode equipped with a gelled ionic liquid, 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)amide (C(8)mimC(1)C(1)N), as a salt bridge, was examined in the potentiometry of pH standard solutions. The variation in the liquid junction potential (LJP) of the ionic liquid (IL)-type reference electrode, measured with respect to a double junction-type KCl reference electrode, was within 1 mV when one standard solution was replaced by another, except for the phthalate standard. The time course of the potential of the IL-type reference electrode showed a standard deviation of ±0.

Kinetics of ion transfer at the ionic liquid/water nanointerface.

Ion transfer (IT) processes in ionic liquids (ILs) are essential for their applications in electrochemical systems and chemical separations. In this Article, the first measurements of IT kinetics at the IL/water interface are reported. Steady-state voltammetry was performed at the nanometer-sized polarizable interface between water and ionic liquid, [THTDP(+)][C(4)C(4)N(-)], immiscible with it that was formed at the tip of a nanopipet.

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.

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.

Ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, probed by x-ray reflectivity measurements.

The presence of ionic multilayers at the free surface of an ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide ([TOMA(+)][C(4)C(4)N(-)]), extending into the bulk from the surface to the depth of approximately 60 A has been probed by x-ray reflectivity measurements. The reflectivity versus momentum transfer (Q) plot shows a broad peak at Q approximately 0.4 A(-1), implying the presence of ionic layers at the [TOMA(+)][C(4)C(4)N(-)] surface.

Orientation correlation of sulfosuccinate-based room-temperature ionic liquids studied by polarization-resolved hyper-Rayleigh scattering.

Hyper-Rayleigh scattering (HRS) of sulfosuccinate-based room-temperature ionic liquids (RTILs), tetraalkylammonium salts of bis(2-ethylhexyl)sulfosuccinate (BEHSS(-)) and di(isobutyl)sulfosuccinate (DIBSS(-)), shows strong orientation correlation between sulfosuccinate ions for both BEHSS(-)-based and DIBSS(-)-based RTILs. The hyperpolarizability and polarization resolved HRS, giving information at the dipolar electric order and at the quadrupolar electric order, respectively, have been measured as a function of the distance between sulfosuccinates by changing the size of the tetraalkylammonium ions constituting the ionic liquids. The variations obtained for the dipolar electric and quadrupolar electric components of the HRS intensity show the orientation correlation between sulfosuccinate ions.

Imaging of the liquid-liquid interface under electrochemical instability using confocal fluorescence microscopy.

The onset of the electrochemical instability has been imaged at the 1,2-dichloroethane (DCE)|water (W) interface modified with a fluorescent phospholipid using confocal fluorescence microscopy (CFM). Heterogeneously fluorescent images are recorded successively under the transfer of dodecyl sulfate ions (DS-) across the interface, which induces the irregularly increased current in a voltammogram. The commencement of the hydrodynamic movement of the solutions due to the electrochemical instability has been detected as the appearance of dark domains at the edge of the interface, that is, the three-phase contact of the DCE-W-glass wall confining the interface.

Phase transition of a binary room-temperature ionic liquid composed of bis(pentafluoroethanesulfonyl)amide salts of tetraheptylammonium and N-tetradecylisoquinolinium and its surface properties at the ionic liquid|water interface.

A binary room-temperature ionic liquid (RTIL) composed of bis(pentafluoroethanesulfonyl)amide (C(2)C(2)N(-)) salts of tetraheptylammonium (THpA(+)) and N-tetradecylisoquinolinium (C(14)Iq(+)) undergoes a phase transition upon increasing the mole fraction of C(14)Iq(+) (x) in the bulk RTIL. The initial decrease with x of the interfacial tension (gamma) at the interface between water (W) and the binary RTIL reaches a break point at x approximately 0.2 irrespective of the values of the phase-boundary potential.

Potential-dependent adsorption of decylsulfate and decylammonium prior to the onset of electrochemical instability at the 1,2-dichloroethane|water interface.

The adsorption of decylsulfate (DeSO4(-)) and decylammonium (DeNH(3+)) at the 1,2-dichloroethane (DCE)|water(W) interface has been examined as a function of the phase-boundary potential by simultaneous recording of electrocapillary curves and voltammograms. The standard Gibbs energies for the adsorption of DeSO(4)(-) and DeNH(3)(+) at the DCE|W interface from the W phase depend linearly on the phase-boundary potential, having the slopes of 9.1 and-9.

Ultraslow response of interfacial tension to the change in the phase-boundary potential at the interface between water and a room-temperature ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide.

Ultraslow response, on the order of minutes, of the interfacial tension to the change in the phase-boundary potential at the interface between water and a room-temperature ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, has been demonstrated. This ultraslow relaxation, which is not observed at the interface between two immiscible electrolyte solutions made of molecular organic solvents, is likely to be due to the long-range and collective ordering of ions of the electrical double layer on the ionic liquid side of the interface.

Use of highly hydrophobic ionic liquids for ion-selective electrodes of the liquid membrane type.

The phase-boundary potential at the interface between an aqueous KCl solution (W) and a hydrophobic room-temperature ionic liquid (RTIL), trioctylmethylammonium bis(nonafluorobutylsulfonyl)imide ([TOMA(+)][C(4)C(4)N(-)]), containing dicyclohexano-18-crown-6 (DCH18C6), shows the nernstian response to K(+) in W within a polarized potential window of 500 mV between [TOMA(+)][C(4)C(4)N(-)] and W, demonstrating that hydrophobic RTILs can be used as a nonvolatile ionic medium for liquid-membrane ion-selective electrodes. The complex formation constant of K(+) with DCH18C6 in [TOMA(+)][C(4)C(4)N(-)] is estimated to be on the order of 10(9) from the upper detection limit using a partition equilibrium model in the presence of a neutral ionophore. The response time of the phase-boundary potential is approximately 20 min.

Mutual solubility of hydrophobic ionic liquids and water in liquid-liquid two-phase systems for analytical chemistry.

Liquid-liquid two-phase systems formed by a hydrophobic ionic liquid and water find several useful ways of application in analytical chemistry. One of the most important properties of such two-phase systems is the mutual solubility of the IL and water. Recent advancements on this subject have been reviewed.

Ionic liquid salt bridge in dilute aqueous solutions.

A new type of salt bridge composed of a hydrophobic room-temperature ionic liquid, recently proposed (T. Kakiuchi and T. Yoshimatsu, Bull.

New class of Ag/AgCl electrodes based on hydrophobic ionic liquid saturated with AgCl.

A new type of Ag/AgCl electrodes based on a hydrophobic ionic liquid has been proposed. The electrode consists of a Ag/AgCl electrode immersed in or coated with a AgCl-saturated ionic liquid, 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([C(8)mim+][C(1)C(1)N-]), instead of the internal aqueous solution. The [C(8)mim+][C(1)C(1)N-] phase plays dual roles, that is, as a medium dissolving AgCl and an ionic-liquid-type salt bridge upon contact with an aqueous solution.

Interfacial ion pairing at the interface between water and a room-temperature ionic liquid, N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide.

The specific interaction of N-tetradecylisoquinolinium (C(14)Iq+) with Cl- and Br- has been detected in the voltammetry of ion transfer and electrocapillarity at the interface between an aqueous solution (W) and a room-temperature ionic liquid (RTIL), N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide ([C(14)Iq+][C(2)C(2)N-]). This specific interaction also makes the transfer of Cl- and Br- into [C(14)Iq+][C(2)C(2)N-] energetically more favorable in comparison with that of F- and SO(4)(2-). The width of the polarized potential window in ion-transfer voltammetry at the [C(14)Iq+][C(2)C(2)N-]|W interface is significantly narrower because of the transfer of anions from W to RTIL.

Structure of the electrical double layer on the aqueous solution side of the polarized interface between water and a room-temperature ionic liquid, tetrahexylammonium bis(trifluoromethylsulfonyl)imide.

The structure of the electrical double layer on the aqueous solution side has been studied by measuring electrocapillary curves at the polarized interface between a room-temperature ionic liquid (RTIL), tetrahexylammonium bis(trifluoromethylsulfonyl)imide, and water (W) at different concentrations of LiCl. Thermodynamic analysis of the electrocapillary curves indicates that Li+ ions negatively adsorb at the point of zero charge. The adsorption of Li+ and Cl- ions in the polarized potential window of about 200 mV can be explained by the Gouy's double layer model, and the specific adsorption of Li+ and Cl- ions at the RTIL|W interface is negligible within the polarized potential window.

SECM study of solute partitioning and electron transfer at the ionic liquid/water interface.

Molecular partitioning and electron-transfer kinetics have been studied at the ionic liquid/water (IL/water) interface by scanning electrochemical microscopy (SECM). The ionic liquid C8mimC1C1N is immiscible with water and forms a nonpolarizable interface when in contact with it. Partitioning of ferrocene (Fc) across the IL/water interface was studied by SECM and found to be kinetically fast with a partition coefficient CIL/CW of 2400:1.

Facilitated transfer of alkali-metal cations by dibenzo-18-crown-6 across the electrochemically polarized interface between an aqueous solution and a hydrophobic room-temperature ionic liquid.

The facilitated transfer of alkali metal cations (Li+, Na+, K+, Rb+, Cs+) by dibenzo-18-crown-6 (DB18C6) across the electrochemically polarizable interface between an aqueous solution (W) and a hydrophobic ionic liquid, N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([C18Iq][TFPB]), has been studied using cyclic voltammetry at the interface formed at the tip of a micropipet. In cyclic voltammograms (CVs), the current due to the facilitated transfer of the cations by DB18C6 from W to [C18Iq][TFPB] can be measured within the polarized potential window of the [C(18)Iq][TFPB]|W interface. The stoichiometry of the complexes in [C18Iq][TFPB] for Li+, Na+, K+, and Rb+ are found to be 1:1 while for the Cs+ transfer both 1:1 and 1:2 complexes are likely to be formed.