Mitsuhiro Kanakubo

Experimental evidences for molecular origin of low-Q peak in neutron/x-ray scattering of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids.

Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n > 6 exhibited a characteristic peak in the low-Q range of 0.2-0.4 Å(-1), indicating the heterogeneity of their ionic liquids. SANS profiles I(H)(Q) and I(D)(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles ΔI(Q) [=I(D)(Q) - I(H)(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S(Q) (peak)(r). The S(Q) (peak)(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 Å for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm.

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.

High pressure studies of the transport properties of ionic liquids

High pressure measurements have been made of viscosities, ion self-diffusion coefficients and electrical conductivities of ionic liquids, mainly of imidazolium salts. We review how these properties have been analysed in terms of the empirical Stokes-Einstein, Walden and Nernst-Einstein equations, and examine trends revealed by the phenomenological approach of velocity correlation coefficients and the more general theory of density scaling. Finally we examine the possibility of dynamic crossover in the transport properties of ionic liquids.

Transport, electrochemical and thermophysical properties of two N-donor-functionalised ionic liquids

Two N-donor-functionalised ionic liquids (ILs), 1-ethyl-1,4-dimethylpiperazinium bis(trifluoromethylsulfonyl)amide (1) and 1-(2-dimethylaminoethyl)-dimethylethylammonium bis(trifluoromethylsulfonyl)amide (2), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (3). Marked differences in thermal and electrochemical stability were observed between the two tertiary-amine-functionalised salts and the non-functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self-diffusion coefficients (Di ) and molar conductivities (Λ) are higher for the IL with an open-chain cation (2) than that with a cyclic cation (1), but less than that with a non-functionalised, heterocyclic cation (3). The viscosities (η) show the opposite behaviour. The Walden [Λ[proportionality](1/η)(t) ] and Stokes-Einstein [Di /T)[proportionality](1/η)(t) ] exponents, t, are very similar for the three salts, 0.93-0.98 (±0.05); that is, the self-diffusion coefficients and conductivity are set by η. The Di for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13% higher than that of 2. The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D+ +D- ). The Nernst-Einstein deviation parameters (Δ) are such that the mean of the two like-ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3, 1 and 2, respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order D(d)__ < D(d)++ < D(d)+_, as is common for [Tf2N](-) salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti-correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti-correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t~0.95.

Physical and CO2-Absorption Properties of Imidazolium Ionic Liquids with Tetracyanoborate and Bis(trifluoromethanesulfonyl)amide Anions

Ionic liquids with tetracyanoborate ([TCB]−) and bis(trifluoromethanesulfonyl)amide ([Tf2N]−) anions generally have low viscosities and high CO2 capacities, and thus they are attractive solvents for CO2-related applications. Herein, we have investigated physical and CO2-absorption properties of 1-ethyl-3-methylimidazolium tetracyanoborate ionic liquid ([emim][TCB]) to discuss the anion effects of [TCB]− in comparison with the previous results of [emim][Tf2N]. The density, viscosity, electrical conductivity, and isobaric molar heat capacity were measured as a function of temperature at atmospheric pressure. [emim][TCB] has both lower density and isobaric molar heat capacity than [emim][Tf2N]. [emim][TCB] shows superior transport properties (lower viscosity and higher electrical conductivity) compared to [emim][Tf2N], whereas the Walden plots of molar conductivity against fluidity (reciprocal of viscosity) have smaller values in [emim][TCB] than in [emim][Tf2N] at certain fluidities. The high-pressure CO2 solubilities were also determined in [emim][TCB]. The mole fraction scaled solubility of CO2 in [emim][TCB] is slightly larger than that in [emim][Tf2N] at certain pressures and temperatures. The former ionic liquid shows much higher molarity scaled solubility of CO2 than the latter because of the smaller molar volume. It is suggested that both anions have similar strength of intermolecular interaction with CO2 and comparable changes in the solvent structure between neat and CO2 solution, in view of the thermodynamic parameters of dissolution.

Relation between Volume Expansion and Hydrogen Bond Networks for CO2−Alcohol Mixtures at 40 °C

We experimentally determined the density and mole fraction of CO(2) (x(CO(2))) for CO(2)-alcohol (methanol, ethanol, propanol, butanol, isopropyl alcohol, and tert-butyl alcohol) mixtures and performed molecular dynamics (MD) simulations to study the mechanisms of volume expansion at 40 °C. The volume as calculated by vapor-liquid equilibrium (VLE) data increased with decreasing alkyl chain length, although there was no effect of branched alkyl groups. Analysis of the hydrogen bond network showed that the average number of hydrogen bonds per alcohol molecule decreased with increasing branched methyl groups. At pure alcohol condition, large size hydrogen bond networks were made. With further addition of CO(2) molecules, it became difficult to contain the large hydrogen bond networks. Furthermore, the hydrogen bond networks changed to a cyclic pentamer or tetramer, and volume expansion occurred.

Formation of Self-Ordered TiO2 Nanotubes by Electrochemical Anodization of Titanium in 2-Propanol/ NH4F

Ti0 2 nanotubes (TiNTs) were formed by the electrochemical anodization of titanium in 2-propanol/water containing 0.14 M NH 4 F as the supporting electrolyte. The effects of the water content, time of anodization, and potential on the growth behavior of TiNT were studied. At the optimum solvent composition of 16 vol % water/84 vol % 2-propanol, the reaction was kinetically controlled. The TiNTs obtained under optimum conditions had heights of up to 1800 nm and inner diameters of about 90 nm. Increasing the potential beyond 20 V did not improve the quality of the nanotubes because of the introduction of disordering. The scanning electron microscopy and X-ray diffraction analysis revealed a preferred growth direction of the TiNTs relative to the substrate surface. A thin barrier layer existed at the nanotubes/metal interface, which was also confirmed by ellipsometry. This barrier layer was enriched with the rutile phase whereas the nanotubes were enriched with the anatase phase.

Determination of anisotropic solvation structure of octafluorotoluene in supercritical carbon dioxide by means of solvent-induced 19F NMR chemical shift

Abstract 19 F NMR chemical shifts of octafluorotoluene and hexafluorobenzene in dilute carbon dioxide solutions were precisely determined at a fixed temperature of 314.4 K over a wide range of pressure from 1 to 35 MPa. We newly present the analytical procedure to determine anisotropic solvation structure by means of a solvent-induced 19 F NMR chemical shift. The anisotropic solvation structure around octafluorotoluene in supercritical carbon dioxide was discussed in comparison with a more symmetric geometry of hexafluorobenzene.

Numerical simulation of two-dimensional piston effect and natural convection in a square cavity heated from one side

Piston effect and natural convection in two-dimensional square cavity heated from one side are solved numerically in which it is assumed that the temperature of the left-hand-side wall is suddenly increased at t=0. According to the piston effect, the bulk temperature suddenly rises and convection cells are generated near not only hot wall but also cold wall. However, the rise of temperature due to natural convection has no influence on the piston effect, because the difference in time scale between the natural convection and piston effect is very large

Solid-phase intramolecular oxyselenenylation and deselenenylation reactions using polymer-supported selenoreagents and their application to aqueous media organic synthesis

Polymer-supported organoselenium reagents with amide linker were readily prepared from substituted-polystyrene resins. Through the use of polymer-supported arylselenenyl bromides, the oxyselenenylation reaction of olefins was carried out even in water. An amphiphilic polymer-supported arylselenenyl bromide was employed, and the intramolecular oxyselenenylation and the subsequent deselenenylation reactions proceeded smoothly in water with fair chemical yields (up to an 83% total yield).