藤田 正博

Two types of thermotropic smectic phase and of anisotropic ion conduction were observed in an amphiphilic ionic liquid, N-ethyl-N'-dodecylimidazolium dodecyl sulfonate/lithium tetrafluoroborate mixture.

Aliphatic and alicyclic ammonium inner salts containing an ether bond were prepared as a new family of zwitterionic liquids. Ether bond is not only effective for lowering melting points of ammonium-type zwitterions but also interesting to realize unique solid-solid transition.

Novel ionic liquids (ILs) composed of azole type cation and anion were prepared. Triazole and tetrazole were coupled with 1-ethyl-3-methylimidazolium hydroxide. Obtained tetrazole salt was liquid at room temperature showing only glass transition temperature at −89 °C. The ionic conductivity reached to 8.9 × 10⁻³ S cm⁻¹ at room temperature reflecting low viscosity of 42.5 cP at 25 °C. This is the first report on the ILs based on only azole type ions.

We have prepared polymer gel electrolytes with alkali metal ionic liquids (AMILs) that inherently contain alkali metal ions. The AMIL consisted of sulfate anion, imidazolium cation, and alkali metal cation. AMILs were mixed directly with poly(3-sulfopropyl acrylate) lithium salt or poly(2-acrylamido-2-methylpropanesulfonic acid) lithium salt to form polymer gels. The ionic conductivity of these gels decreased with increasing polymer fraction, as in general ionic liquid/polymer mixed systems. At low polymer concentrations, these gels displayed excellent ionic conductivity of 10(-4) to 10(-3) S cm(-1) at room temperature. Gelation was found to cause little change in the Li-7 diffusion coefficient of the ionic liquid, as measured by pulse-field-gradient NMR. These data strongly suggest that the lithium cation migrates in successive pathways provided by the ionic liquids. (C) 2004 Elsevier Ltd. All rights reserved.

The ionic conductivity of highly deproteinized liquid natural rubber having epoxy group (LEDPNR) mixed with alkali metal salts was investigated through impedance analysis to clarify the effect of proteins present in the rubber. The LEDPNR, thus used, was prepared from depolymerization of epoxidized natural rubber (ENR) latex, which was deproteinized by incubation of the latex with proteolytic enzyme and surfactant. The ionic conductivity of the resulting LEDPNR was dependent upon the alkali metal salts, where the ionic conductivity of LEDPNR/bis(trifluoromethane sulfonyl)imide (LiTFSI) was higher than that of LEDPNR/lithium perchlorate (LiClO4). The difference in the ionic conductivity was attributed to the solubility of the salts through both high-resolution solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy and measurements of spin-lattice relaxation time. The ionic conductivity of LEDPNR/LiTFSI was also dependent upon concentration of LiTFSI and the conductivity reached the highest value at 20 wt.%, which was different from the monotonic increase in the ionic conductivity of liquid ENR prepared from untreated natural rubber latex. (C) 2004 Elsevier B.V. All rights reserved.

Ionic liquid-type polymer brushes having different hydrocarbon (HC) chain lengths between polymerizable group and imidazolium ring were synthesized. When the carbon number of HC chain was 6, the ionic liquid-type polymer brush exhibited the highest ionic conductivity of 1.37 x 10(-4) S cm(-1) at 30 degreesC reflecting low T-g of -60 degreesC. Moreover, for the first time, we succeeded in obtaining transparent and flexible films without considerable decrease in the ionic conductivity as compared with that of corresponding monomers by using suitable cross-linkers. The most ion conductive (1.1 x 10(-4) S cm(-1) at 30 degreesC) film was obtained when tetra(ethylene glycol)diacrylate was used 0.5 mol% to ionic liquid monomer as the cross-linker. This film is one of excellent conductive films among single-ion conductive materials. (C) 2004 Elsevier Ltd. All rights reserved.

Anisotropic ion-conductive materials have been prepared by self-assembly of a conventional ionic liquid and a hydroxyl-terminated liquid crystal. These assemblies form phase-segregated layered structures on the nanometer scale. Anisotropic ionic conductivities along the direction parallel and perpendicular to the layer have been successfully measured for the sample forming oriented monodomains. The ionic conductivity parallel to the layer (sigma(i//)) is higher than that perpendicular to the layer (sigma(iperpendicular to)). The maximal anisotropy (sigma(i//)/sigma(iperpendicular to)) is 2.6 x 10(3) at 37degreesC in the smectic B phase.

We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Bronsted acids and bases to form salts with melting points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such "protic ionic liquids" exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by boiling, when the total vapor pressure reaches one atm, and the difference in pK(a) value for the acid and base determined in dilute aqueous solutions. For DeltapK(a) values above 10, the boiling point elevation becomes so high (>300 degreesC) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bonding of acid molecules to the proton-transfer anion is strong enough that boiling points, but not melting points, may maximize at the hydrogen-bonded dianion composition. High boiling liquids of this type constitute an interesting class of high-temperature protonic acid that may have high-temperature fuel cell applications.

As a further example of the extraordinary solvent powers of ambient temperature molten salts (ATMS or "ionic liquids'') we demonstrate that lithium thiophosphate glasses, well known for their unicationic conduction mechanism, and high ambient conductivity, dissolve in the ATMS ethylmethylimidazolium tetrafluoroborate up to 30 mol %. Remarkably, the conductivity of this solution is higher than that of a solution of the same lithium salt content made with the salt lithium TFSI [bis(trifluoromethanesulfonyl)imide] which bestows high conductivity on most other solvents. The glass-saturated melt has almost the same conductivity as the glass itself. However their glass temperatures differ by some 200 K so it is clear that the solution retains little if any of the decoupled Li+ conduction mechanism of the glass. It may nevertheless make a suitable electrolyte for lithium cells of a novel kind. Since the ionic liquids may be incorporated in polymer gel electrolytes without significant loss of conductivity, the present solutions may prove valuable for solid-state electrochemical device applications. (C) 2003 The Electrochemical Society.

Modification of cytochrome c (cyt.c) by poly(ethylene oxide) (PEO) chains enabled the protein soluble in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid without denaturation. However, as the solution was full of ions, suitable supporting electrolyte (KCl) was essential for the electron transfer reaction of cyt.c in the ionic liquid to attain adequate ion size for the active center.

A series of liquid crystalline molecules, alpha,omega-bis{4-[(4'-pentyloxy (or -octyloxy)-4-biphenylyl)-carbonyloxy]phenyl}oligo(oxyethylene)s, was synthesized to prepare oriented oligo(oxyethylene) chains. The complexes with LiCF3SO3 spontaneously formed a smectic phase. Since a rigid rod part cannot solubilize the inorganic salts, the oxyethylene moieties form the ion-conductive layers in the smectic phase. The anisotropic ionic conductivity was measured by an impedance analyzer with gold comb-shaped electrode deposited on a glass substrate between Au teeth. The ionic conductivity between the gold teeth increased to 10(-3) S cm(-1) at 142 degreesC, but it dropped considerably to 10(-4) S cm(-1) above that temperature. The temperature corresponded to the isotropization point of the complex. Homeotropic orientation of the liquid crystalline complex enables to make a successive ion-conducting pathway, which is effective to obtain higher ionic conductivity. The effect of the added salts on the ionic conductivity was also analyzed. Higher ionic conductivity was obtained when the liquid crystals were complexed with LiCF3SO3. There is a suitable ion size for prompt ion migration in the oriented polyether. (C) 2002 Elsevier Science B.V. All rights reserved.

Novel ionic liquids containing alkali metal ions as component were prepared by the neutralization of N-ethylimidazole with various kinds of hydrogen sulfates (MHSO4; M = Li, Na, or K). All salts were obtained as transparent viscous liquids at room temperature. These ionic liquids showed ionic conductivity higher than 10(-4) S cm(-1) at room temperature, reflecting low glass transition temperature of below -60degreesC. This is the first report on alkali metal salts which are inherently liquid state at room temperature.

Full Paper: Liquid-crystalline compounds 1 and 3 having perfluoroalkyl-terminated mesogens at both ends of poly(ethylene oxide) chains have been prepared. These compounds show smectic A (S-A) and C phases over 100 degreesC. The 8(X) Iso (isotropic) transition temperatures are higher by about 10 degreesC than those of the corresponding alkyl-substituted compounds 2 and 4. The incorporation of lithium triflate into 1 resulting complexes. The conplexes of 1 and 3 containing 50 mol-% of lithium triflate exhibit columnar phases. The ionic conductivities of the homotropically aligned complexes based on 1 along the direction perpendicular to the molecular director of the S-A phases are higher than those of the corresponding compound of 2. The increase of the ionic conductivities as well as the stabilization of the smectic phases for these perfluoroalkyl-terminated compounds may be due to the formation of more stabilized layered structures through the intermolecular interactions among the persluoroalkyl moieties.

Four kinds of triple ion-type imidazolium salts have been prepared. These salts consist of an imidazolium cation incrporating two sulfonate groups, which is anticipated to provide a single-ion conductive matrix. The melting point of some of these was over 200 degrees C, whereas both sodium salts having methyl group on the imidazolium ring showed only a glass transition temperature at around 20 degrees C. They showed the highest ionic conductivity among these triple ion-type imidazolium salts. Since these imidazolium ions are rather large, the predominant mobile species will be the small counter-cation. These salts certainly open up new possibilities for functional ionic liquids.

Amphiphilic ionic liquid derivatives form self-organized lamellar liquid crystals with room temperature ionic liquids. The ionic conductivities along the smectic layers have been obtained for the samples aligned in the cells with electrodes. The highest value is 4.3 x 10(-2) S cm(-1) at 139degreesC.

A series of new ionic liquids were prepared by neutralizing five different imidazole derivatives with two imide-type acids such as bis(trifluoromethanesulfonyl)imide and bis(perfluoroethylsulfonyl)imide, and their ionic conductivity and thermal properties were investigated. All the imidazolium salts synthesized are liquid at room temperature. The ionic liquid of the methylimidazolium bis(trifluoromethanesulfonyl)imide system has the best ionic conductivity, 7.23 x 10(-3) S cm(-1) at 25 degreesC, of the series of five imidazolium salts. (C) 2001 The Electrochemical Society.

Poly(ethylene oxide) (PEO) derivatives having both vinyl group and imidazolium salt structure on their ends were prepared and polymerized. Molten salt-type polymer brushes having different ethylene oxide (EO) unit number and different tethering structure were prepared to analyze the effect of flexible spacer. The ionic conductivity and DSC measurement of molten salt-type polymer brushes were carried out. When the counteranion species of the polymer was TFSI-, molten salt polymer (1) in spite of rubber-like properties showed high ionic conductivity (1.49 x 10(-4) S cm(-1) at 30 degreesC) corresponds to that of monomers reflecting low T-g (- 56 degreesC). The PEO-tethering of molten salt with polymer matrix was effective to suppress the drop of ionic conductivity after polymerization. Three kinds of imidazolium cations, such as n-ethylimidazolium, n-methylimidazolium or 1-benzyl-2-methylimidazolium, were selected, and corresponding monomers were synthesized. These were polymerized to analyze the effect of terminal cationic structure on the ionic conductivity. In spite of different imidazolium cation, the ionic conductivity and T-g of macromonomers and their polymers were equivalent. The ionic conductivity of molten-salt polymers increased with increasing EO or ethylene unit number. It is suggested that the distance between vinyl polymer and terminal imidazolium cation was important factor with respect to high ionic conductivity for molten salt-type polymer brushes. (C) 2001 Elsevier Science Ltd. All rights reserved.

Liquid-crystalline dimeric molecules consisting of rigid mesogenic cores and flexible oxyethylene spacers have been prepared. The ethoxy carbonyl and alkoxy groups are attached to the ends of the mesogenic cores. These molecules have been complexed with lithium triflate, resulting in thermal stabilization of the mesophases. Ionic conductivities along the direction perpendicular to the molecular director of the smectic A phases have been measured for these complexes.

We synthesized a series of imidazolium cations containing covalently-bound anionic sites, such as sulfonate or sulfonamide groups. These zwitterionic imidazolium salts were found to form molten salts just like ordinary imidazolium salts. However, regardless of the high ion density, these ions cannot migrate along potential gradients induced in the bulk. This is a new and unique characteristic in molten salts. When other salts were added to this, the ions generated from the newly added salts were able to behave as carrier ions. The ionic conductivity of a pure molten salt was 10(-9) S cm(-1) at 25 degreesC, but jumped to 10(-5) S cm(-1) by adding an equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at 50 degreesC. The zwitterionic salt having a sulfonamide group instead of sulfonate had an ionic conductivity of 10(-4) S cm(-1) at 50 degreesC after adding an equimolar amount of LiTFSI. These zwitterionic imidazolium salts having vinyl groups were synthesized and polymerized. In spite of their rubber-like properties they showed excellent ionic conductivities of around 10(-5) S cm(-1) at 50 degreesC following the addition of an equimolar amount of LiTFSI to the imidazolium cation unit.

Poly(ethylene oxide) (PEO) of molecular weight 1000 (PEO1000) containing lithium benzenesulfonate (LiBs) (PEO1000/LiBs), PEO derivatives having benzenesulfonate groups on both chain ends (PEO1000-(BSLi)(2)), or 1-ethyl-2,3-dimethylimidazolium bromide (ImB), were each blended with natural rubber (NR). The ionic conductivity was measured from AC impedance values. The ionic conductivity of the mixture of NR and PEO1000/LiBs (40 wt%) was about 10(-6) S cm(-1) at 50 degrees C; this mixture retained rubbery physical characteristics. At NR content of 10 wt%, the ionic conductivity of the mixture (NR/PEO1000/LiBs) was 2.7 x 10(-5) S cm(-1) at 50 degrees C, approximately 10 times higher than that of the bulk PEO/LiBs mixture. For mixtures of NR and PEO1000-(BSLi)(2), no improvement in ionic conductivity by mixing was found. The ionic conductivity of the mixture of NR and ImB was about 10 times higher than for the bulk of PEO1000-(BSLi)(2) at a NR content of 10 wt%. We propose that the ionic conductivity of the mixture increases when an ion conducting matrix containing simple salt is added. On the other hand, the DSC curve for NR/PEO derivatives showed two T(g)s based on the separate components, suggesting phase separation of the PEO derivative in the NR phase. (C) 2000 Elsevier Science Ltd. All rights reserved.

Poly(ethylene oxide) (PEO) derivatives having a positively-charged group on the chain end were prepared to analyze anion conduction mechanism in the polyether moiety. Effects of the terminal group structure and anion species on the anionic conductivity were analyzed. The anionic conductivity of PEO-onium salts was about 10(-4) S cm(-1) at room temperature, which was much higher than that for corresponding cation conductors. This difference should be based on much weaker interaction force of ether oxygens toward anions than that for cations. The ionic conductivity was evaluated under the same segmental motion by normalizing the different glass transition temperature (T-g). As a result, reduced ionic conductivity was nearly equal among all kinds of anion and cation conductive PEO oligomers having charged group on the chain end. The T-g was revealed to mainly govern the ionic conductivity of the matrix. Since the interaction between anion and ether oxygen was certainly detected but it was weak to suppress the elevation of T-g, lower T-g and corresponding high ionic conductivity were observed in these anion conductive polyethers. (C) 2000 Elsevier Science Ltd. All rights reserved.

Poly(ethylene oxide) (PEO) derivatives having both vinyl group and imidazolium salt structure on their ends were prepared and polymerized. When molten salt domain was provided by changing chloride anion with bis(trifluoromethanesulfonylimide) anion, excellent ionic conductivity (1.20 x 10(-4) Scm(-1) at 30 degrees C) was observed in spite of rubber-like properties.