2005

Time of Presentation:Dec 17 9:30 AM - 10:00 AM  Oral Invited
Subject Area:Advances in Nanochemistry at Liquid Interfaces
Structure of the electrical double layer at the interface between hydrophobic room-temperature molten salt and water
T. Kakiuchi 
Two-phase systems composed of an aqueous solution and a room-temperature molten salt (RTMS, also called ionic liquid), provide promising alternatives of conventional two phase systems that consist of a volatile organic compound and water. The interface in such two-phase systems, electrical double layers presumably exist on both sides of the interface. We will show from electrocapillarity studies of this new electrochemical interface that there is no specific adsorption of lithiuim ions at the interface from the aqueous side of the interface. In contrast, 1-octyl-3-methylimidazolium cations adsorb at interface.

Time of Presentation:Dec 17 8:00 PM - 10:00 PM Poster
Subject Area:Advances in Nanochemistry at Liquid Interfaces
Conceptually new salt-bridge made of hydrophobic room-temperature molten salts
T. Yoshimatsu1; N. Nishi1; M. Yamamoto1; T. Kakiuchi1
We propose a new type of salt-bridge using hydrophobic room-temperature molten salt (RTMS) based on the phase-boundary potential difference across hydrophobic RTMS/water interface.
The phase-boundary potential difference across 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl) imide ([C8mim][C1C1N])/water interface is determined primarily by the partition of C8mim+ and C1C1N- ions. The cell voltage was stable within 1.0 mV over the extended period of time when the aqueous phase contains x mM (x = 1~2000) HCl, LiCl, NaCl or KCl. Plots of the voltage against the logarithm of the activity of the electrolyte in the water phase were all straight lines over the wide range of the concentration. This slope reflects the Nernstian response of the Ag/AgCl electrode and confirms that the phase-boundary potential is independent of the type and concentration of the electrolytes in the aqueous phase. The ([C8mim][C1C1N] gelified using poly(vinylidenefluoride-co-hexafluoropropyrene) yielded the same results.
     HCl    LiCl     NaCl     KCl
RTMS     -55.7±0.6     -57.1±0.3    -57.8±0.5     -59.3±0.4
RTMS gel     -57.0±0.6    -57.1±0.3     -56.6±0.4     -59.0±0.5

Dec 18 10:45 AM - 11:15 AM Oral Invited
Subject Area:Electroanalytical Chemistry 
Electrochemistry at the interface between hydrophobic room-temperature molten salt and water
T. Kakiuchi
Upon contact with an aqueous phase, a hydrophobic molten salt that is in the liquid state at room temperature (ionic liquid) can form either polarized or nonpolarized interface, depending on the hydrophobicity of the constituent ions and also on the type of the ions dissolved in the aqueous phase. By judiciously choosing the ions for the molten salt and the aqueous electrolyte solution, we can assemble the molten-salt|water interface that enables us to study the charge transfer across the interface using conventional voltammetric techniques. We will show some examples of the voltammetry of ion transfer, facilitated ion transfer and electron transfer across the molten-salt|water interface.

Time of Presentation:Dec 18 8:00 PM - 10:00 PM Poster
Subject Area:Electroanalytical Chemistry
Effect of the two-dimensional array of phase-separated binary self-assembled monolayers on electron transfer reaction
H. Tomono1; P. H. Pham1; N. Nishi1; M. Yamamoto1; T. Kakiuchi1
On binary thiol self-assembled monolayers (SAMs) consisting of positively-charged and negatively-charged domains, the redox reaction occurs at the domains where there is the electrostatic interaction between the redox species and the terminal group of alkanethiolate derivaties forming the domains. The rate of the electron transfer is expected to depend on the area and the shape of the redox-active domains. Binary SAMs of 11-amino-1-undecanethiol, hydrochloride (AUT) and 3-mercaptopropionic acid (MPA) were first formed and, then, MPA domains were replaced with 11-mercaptoundecanoic acid (MUA) by selective reductive desorption of MPA. Cyclic voltammograms (CVs) of redox reaction of Ru(NH3)3+/2+ on the phase-separated binary SAMs and the MUA-SAMs showed similar magnitudes of current and the peak separation. Because the size of the domains is in several tens nanometer across, it seems that Ru(NH3)63+/2+ ions may be transported to the redox-active surface from adjacent redox-inactive domains.

Dec 18 8:00 PM - 10:00 PM Poster
Subject Area:Electroanalytical Chemistry 
Importance of the detailed shape of the interface at the orifice of a micropipette in voltammetry of ion transfer across the room-temperature molten salt and water
S. Imakura1; N. Nishi1; T. Kakiuchi1
We recently proposed a new polarized interface between a hydrophobic room-temperature molten salt (RTMS) composed of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion (TFPB) and N-octadecylisoquinolinium cation (C18Iq) and water, which shows a wide potential window. The use of a micropipette technique is only one practical method in measuring voltammogram of charge transfer at this new interface because of the high viscosity of the RTMS. By using such a micropipette technique, we were able to detect the ion transfer across the interface between [C18Iq][TFPB] and water. However, the shape of the voltammograms cannot be explained with a simple linear or spherical diffusion model. The shapes of the voltammograms are strongly influenced by the shape of the interface and also that of the micropipette. We will show, by using digital simulation, that the shape of the voltammograms can be quantitatively explained by taking account of these geometrical factors.

Dec 18 8:00 PM - 10:00 PM Poster
Subject Area: Electroanalytical Chemistry 
Effect of the interfacial area on the electrochemical instability at the 1,2-dichloroethane/water interface
Y. Kitazumi1; N. Nishi1; M. Yamamoto1; T. Kakiuchi1
The concept of the electrochemical instability explains the existence of irregular currents in the transfer of ionic surfactants across the liquid|liquid interface. However, the generating mechanism of the electrochemical instability is still unclear. To clarify the mechanism, cyclic voltammograms were recorded for the transfer of surfactant ions across a 1,2-dichloroethane|water (DCE|W) interface varying the interfacial area, the scan rate and the concentration of the surfactant ions. The electrochemical measurements on the DCE|W interface supported at the tip of a micropipette having the inner diameter of 25 micrometers were made without the compensation of the solution resistance. When the concentration of the surfactant ions is higher, voltammograms showed irregular currents due to the electrochemical instability. This demonstrates that the electrochemical instability is not associated with the positive feedback usually employed in voltammetry using conventional flat interfaces. The microscopic observation of the interface formed at the tip of the micropipette showed that the instability of the interface does not necessarily induce the irregular currents in the voltammograms.


Dec 18 8:00 PM - 10:00 PM Poster
Subject Area:Ionic Liquids: Perspectives on the Present, Visions for the Future 
Facilitated transfer of cations by dibenzo-18-crown-6 across the polarized interface between water and N-octadecylisoquinolinium tetrakis[3,5-bis (trifluoromethyl)phenyl]borate
H. Murakami1; S. Imakura1; N. Nishi1; T. Kakiuchi1
Facilitated transfer of cation (H+, Li+, Na+, K+, Rb+, Cs+, Ba2+, Sr2+, La3+) by dibenzo-18-crown-6 (DB18C6) across the polarized micrometer-sized interface between water (W) and N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([C18Iq][TFPB]) is studied using cyclic voltammetry with micropipettes under conditions that the concentration of DB18C6 in [C18Iq][TFPB] is much smaller than the concentration of cations in water.
When the scan rate is slow enough (10 mV/s), voltammograms showed the steady-state current. When the scan rate is not slow enough, a peak appeared both in forward and reverse scans. We evaluated the formation constants of cations with DB18C6 in C18IqTFPB by comparing the shape of voltammograms experimentally obtained with those calculated with digital simulation.

Dec 19 8:10 AM - 8:30 AM Oral
Subject Area:Ionic Liquids: Perspectives on the Present, Visions for the Future 
Optical second harmonic generation study on the interfaces between water and hydrophobic room temperature molten-salts composed of aromatic quaternary ammonium cations
N. Nishi1; S. Imakura1; M. Yamamoto1; T. Kakiuchi1
The interfaces between water and hydrophobic room temperature molten-salts (RTMSs) composed of aromatic quaternary ammonium cations have been studied using optical second harmonic generation (SHG). The RTMSs used are [N-dodecylpyridinium][bis(perfluoroethylsulfonyl)imide] ([C2C2N]), [alkylbenzyldimethylammonium][C2C2N] with the chain length of 12-18, [N-dodecylisoquinolinium][C2C2N], [4-phenyl-N-dodecylpyridinium][C2C2N] and [N-octadecylisoquinolinium][tetrakis[3,5-bis(trifluoromethyl)phenyl]borate]. Orientation of the SHG-active cations at the RTMS|water interfaces has been analyzed by measuring the dependence of the SH intensity on the polarization of fundamental and SH light and compared with that at the RTMS|air interfaces. The orientation analysis has revealed that the azimuthal distribution of cations at RTMS|water and RTMS|air interfaces is isotropic and that the transition dipole moments of the cations at the RTMS|water interfaces are nearly parallel to the interfaces whereas at the RTMS|air interfaces they are tilted at 50C from the normal surface.
 

F19 Molecular dynamics simulation of the room temperature molten salt:2-Octadecylisoquinolinium/Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (C18Iq+/TFPB-) （京大） ○VladimirViktorovichSOKOLOV,西　直哉,山本雅博,垣内　隆
F28 Tetrakis[3,5-bis(trifluoromethyl)phenyl]borateからなる常温溶融塩｜水分極性微小界面を横切るイオンの 標準イオン移動電位のボルタンメトリーによる検討 （京大） ○今倉精一,西　直哉,山本雅博,垣内　隆
2F32 N-octadecylisoquinolinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate｜水界面を横切る環状配位子による促進イオン移動のボル タンメトリー （京大） ○村上　浩,今倉精一,西　直哉,山本雅博,垣内　隆

G会場　第 ２日・９月９日（金）
【電気化学反応・基礎一般，測定法】
（10:00〜11:00）
2G07 疎水性常温溶融塩を用いる塩橋の作製と構成イオンの最適化 （京大） ○吉松孝宗,西　直哉,山本雅博,垣内　隆

J会場　第１日・ ９月８日（木）
【シンポジウム：表面電気化学】
　主催：電極表面科学研究懇談会

（13:15〜14:00）
特1J18 金表面における多成分自己組織化単分子膜の電気化学 （京大） 垣内　隆
第２日・９月９日（金）
2J09 Pt(111)面上の水素吸着の第一原理計算：電位依存性 （京大,香港科学技術大） ○山本雅博,TingChanChe