Noriaki Tsuchihashi

Effect of pressure on the transport properties of ionic liquids: 1-alkyl-3-methylimidazolium salts.

The self-diffusion coefficients (D) of the cation and anion in the ionic liquids 1-hexyl-3-methylimidazolium and 1-octyl-3-methylimidazolium hexafluorophosphates ([HMIM]PF6 and [OMIM]PF6) and 1-butyl-3-methylimidazolium and 1-octyl-3-methylimidazolium tetrafluoroborates ([BMIM]BF4) and ([OMIM]BF4) have been determined together with the electrical conductivities (kappa) of [HMIM]PF6 and [BMIM]BF4 under high pressure. The pressure effect on the transport coefficients is discussed in terms of velocity cross-correlation coefficients (VCCs or fij), the Nernst-Einstein equation (ionic diffusivity-conductivity), and the fractional form of the Stokes-Einstein relation (viscosity-conductivity and viscosity-diffusivity). The (mass-fixed frame of reference) VCCs for the cation-cation, anion-anion, and cation-anion pairs are all negative and strongly pressure dependent, increasing (becoming less negative) with increasing pressure. VCCs are the more positive for the stronger ion-velocity correlations; therefore, f+ - is least negative in each case. In general, f- - is less negative than f+ +, indicating a smaller correlation of velocities of distinct cations than that for distinct anions. However, for [OMIM]PF6, the like-ion fii are very similar to one another. Plots of the VCCs for a given ion-ion correlation against fluidity (reciprocal viscosity) show the fij to be strongly correlated with the viscosity as either temperature or pressure are varied, that is, fij approximately fij(eta). The Nernst-Einstein deviation parameter, Delta, is nearly constant for each salt under the conditions examined. It is emphasized that nonzero values of Delta are not necessarily due to ion pairing but result from differences between the like-ion and unlike-ion VCCs, because Delta is proportional to (f+ + + f- - - 2 f+ -). The diffusion and molar conductivity (Lambda) data are found to fit fractional forms of the Stokes-Einstein relationship, (LambdaT) proportional, variant (T/eta)(t) and Di proportional, variant (T/eta)(t), with t=(0.90+/-0.05) for all these ionic liquids, independent of both temperature and pressure within the ranges studied.

Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid–vapor coexistence curve up to the critical temperature. I. NaCl, KCl, and CsCl solutions

The molar conductivities Lambda of NaCl, KCl, and CsCl in liquid methanol were measured in the concentration range of (0.3-2.0) x 10(-3) mol dm(-3) and the temperature range of 60-240 degrees C along the liquid-vapor coexistence curve. The temperature range corresponds to the solvent density range of (2.78-1.55)rhoc, where rhoc = 0.2756 g cm(-3) is the critical density of methanol. The concentration dependence of Lambda at each temperature and density (pressure) has been analyzed by the Fuoss-Chen-Justice equation to obtain the limiting molar conductivity Lambda0 and the molar association constant KA. For all the electrolytes studied, Lambda0 increased almost linearly with decreasing density at densities above 2.0rhoc, while the opposite tendency was observed at lower densities. The relative contribution of the nonhydrodynamic effect on the translational friction coefficient zeta was estimated in terms of Deltazeta/zeta, where the residual friction coefficient Deltazeta is the difference between zeta and the Stokes friction coefficient zetaS. At densities above 2.0rhoc, Deltazeta/zeta increased with decreasing density though zeta and Deltazeta decrease, and the tendencies are common for all the ions studied. The density dependences of zeta and Deltazeta/zeta were explained well by the Hubbard-Onsager (HO) dielectric friction theory based on the sphere-in-continuum model. At densities below 2.0rhoc, however, the experimental results cannot be explained by the HO theory.

Pressure and solvent isotope effects on the mobility of monovalent cations in water

Limiting molar conductivities of alkali metal chlorides (LiCl to CsCl) and tetraalkylammonium bromides (Me4NBr to Bu4NBr) in H2O and D2O were determined at 25 °C as a function of pressure up to 196.1 MPa. The limiting molar conductivities of the ions were obtained with the aid of transference numbers of KCl under high pressure, and transformed into the residual friction coefficients Δζobs to see what kinds of factors are important in the mechanism of ion migration. The pressure and solvent isotope effects on Δζobs of the Li+ ion agree qualitatively with the predictions of the Hubbard–Onsager (HO) dielectric friction theory, which indicates that dielectric friction plays an important role for smaller ions. However, the Cs+ ion shows opposite pressure and solvent isotope effects. For the R4N+ ions, Δζobs increases with an increase in the ionic radius and the pressure, opposite to the predictions of the HO theory. The increase in Δζobs for large R4N+ ions with increasing pressure suggests that the structure ...

Pressure and temperature effects on the excess deuteron and proton conductance

The limiting molar conductances Λ° of deuterium chloride DCl in D2O were determined as a function of pressure and temperature in order to examine the proton-jump mechanism in detail. The excess deuteron conductances λ°E(D+), as estimated by the equation [λ°E(D+) = Λ°(DCl/D2O) − Λ°(KCl/D2O)], increases with an increase in the pressure and temperature as well as the excess proton conductance [λ°E(H+) = Λ°(HCl/H2O) − Λ°(KCl/H2O)]. The isotope effect on the excess conductances, however, depends on the pressure and temperature contrary to the model proposed by Conway et al.: λ°E(H+)/λ°E(D+) decreases with increasing pressure and temperature. The magnitude of the decrease with pressure becomes more prominent at lower temperature. These results are discussed in terms of the pre-rotation of adjacent water molecules, the bending of hydrogen bonds with pressure, and the difference in strength of hydrogen bonds between D2O and H2O.

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

AbstractThe limiting molar conductances Λ0 of potassium deuteroxide KOD in D2O and potassium hydroxide KOH in H2O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH− (OD−) and a H3O+ (D3O+) ion. The excess conductance of the OD− ion in D2O λEO(OD-), as estimated by the equation

Electric conductivities of 1:1 electrolytes in liquid methanol along the liquid-vapor coexistence curve up to the critical temperature. III. Tetraalkylammonium bromides

\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)

Comparison of temperature, pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

increases a little with pressure as well as the excess conductance of the OH− ion in H2O