It is quite important to analyze and design interface between ionic liquid and other materials due to further development of functional interface. In the present study, physicochemical properties of mixtures containing ionic liquids are discussed. In the former part, interests are focused on the dynamic phase change of ionic liquid/water mixtures. Some ionic liquids show lower critical solution temperature type phase change after mixing with water. Component ions required for the realization of this type of phase change are proposed related to the water content. In the latter part, dimension control of ionic liquids is summarized considering the marriage of liquid crystals and ionic liquids. Through these results, importance of interface concerning ionic liquids has been mentioned.
Room temperature ionic liquids (RTILs) are very unique substances which may form interfaces with polar and/or non-polar liquids. Though their physico-chemical properties have been investigated intensively, microscopic and local structural knowledge at the interface is limited and the overall problems related to the interface still remain unsolved. In this paper, we have reviewed our series of experimental results on surfaces or buried interfaces (liquid/liquid interfaces) by using IR-Vis sum-frequency generation vibrational spectroscopy. We demonstrate for the first time the formation of a nonpolar alkyl-chain dividing layer between RTIL ([C4mim]PF6) and an n-alcohol. Heterogeneous and complex systems of such interfaces may explain various functions of ionic liquids occurring at the interfaces.
The total reflection X-ray absorption fine structure (TR-XAFS) technique was applied to adsorbed films at the surface of aqueous solutions of 1-decyl-3-methylimidazolium bromide (DeMIMBr), 1-hexyl-3-methylimidazolium bromide (HMIMBr) and 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF4) mixture, and dodecyltrimethylammonium bromide (DTABr) and dodecyltrimethylammonium tetrafluoroborate (DTABF4) mixtures. The obtained χ spectra were expressed as linear combinations of two specific spectra corresponding to fully hydrated bromide ions (free-Br) and partially dehydrated bromide ions adsorbed to the hydrophilic groups of surfactant ions (bound-Br) at the surface. The proportions of free-and bound-Br ions were evaluated as a function of surface tension and surface composition of the surfactants. The relation between counterion distribution and miscibility of counterions at the solution surface was discussed and the importance of hydrogen bond formation between surfactant cation and counter anion was stressed.
Sputter deposition of metals into a capture medium with extremely low vapor pressure is a simple and convenient method to generate the metal nanoparticles (NPs) without chemical reactions. By careful selection of the capture medium and its temperature, the size of synthesized NPs can be controlled. Sputtering conditions also play an important role in determining the size of NPs. We synthesized Au NPs in a standard ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate by systematically varying the sputtering conditions. It is proved that the temperature of the target and applied voltages have a strong influence on the size of Au NPs, while the working distance between the target and the surface of the capture media, sputtering time, and discharge current have little or no influence. Lower temperatures of the ionic liquid and of the target and higher applied voltage are desired for generating size-controlled smaller NPs.
Homogeneous organometallic as well as organomolecular catalysts were immobilized to the pores of amorphous inorganic supports with the aid of an ionic liquid as Pd-, Cu-, Ru-and Mac-SILC (SILC:Supported Ionic Liquid Layer Catalyst), which is a benign method to immobilize sophisticated but unstable homogeneous catalysts difficult so far to load in an inorganic support by a simple impregnation method. By immobilizing as a SILC, sustainability and reactivity of catalysts increased in Mizoroki-Heck reaction, Suzuki-Miyaura reaction, Huisgen [3+2] cycloaddition (click-reaction) without external ligand in aqueous media and ambient atmosphere, hydrogenation, olefin-metathesis reaction, and asymmetric Diels-Alder reaction. These SILCs could be repeatedly used after filtration.
Ionic liquid has attracted much attention as a stable liquid even in vacuum, which feature has allowed us to propose a new application of the ionic liquid used as a crystallization solvent in a vacuum deposition process. In this review, we introduce a good example of the successful application to the vacuum deposition of single crystals and films of pentacene in ionic liquid. In this ionic liquid-assisted vacuum deposition, the pentacene is found to grow almost under the thermodynamic equilibrium condition with an aid of the ionic liquid, being of very high-quality in crystallinity as compared to those obtained by the simple vacuum deposition process without ionic liquid. The effects of not only the kind, but also the size and shape of the ionic liquids as the solvent on the initial nucleation and the subsequent growth of the pentacene crystal are discussed.
The electric double layer gating technique using ionic liquids which allows to increase the capability of usual field effect doping by two order of magnitude opens a new avenue not only to novel physics of solid-state materials but also to potential applications for dissipationless devices. Here we report high-performance organic field-effect transistors with ionic-liquids electrolytes. With high carrier mobility of 12.6 cm2/Vs in the rubrene crystal that is order of magnitude larger than amorphous silicon devices, pronounced current amplification is achieved at the gate voltage of only 0.2 V, which is two orders of magnitude smaller than that necessary for organic thin-film transistors with dielectric gate insulators. The results demonstrate that the ionic-liquid/organic semiconductor interfaces are suited to realize low-power and fast-switching field-effect transistors without sacrificing carrier mobility in forming the solid/liquid interfaces.