Anomalous Mixing State in Room-Temperature Ionic Liquid-Water Mixtures: N, N -diethyl- N -methyl- N -(2-methoxyethyl) Am
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IN recent decades, molten mixtures in supercooled liquid and glass have drawn much attention. The cation network across the medium range is well developed in mixtures of alkali halides. The network forming of ZnCl2-KCl mixtures is characterized by a ‘‘prepeak,’’ which appears at low-Q in wide-angle neutron scattering (WANS).[1] In molecular dynamics (MD) simulations, a clustering induced by an incomplete mixing at a nanoscopic scale is realized in the simulation box.[2] Environmentally friendly room-temperature ionic liquids (RTILs) are well known to exist as liquids across a wide temperature range instead of as salts.[3,4] The effect of impurities and additives on the physical properties was examined systematically.[3,4] From the viewpoints of thermodynamics, chemical potential, and enthalpy, the mixing effect has been investigated for RTIL-H2O mixtures.[5] The RTILs are 1-butyl-3 methylimidazolium tetrafluoroborate, [C4mim][BF4], and the iodide is [C4mim][I]. Here, a series of cations such as 1-alkyl-3methyl imidazolium is described to be [Cnmim] using the HIROSHI ABE and MASAMI AONO, Doctors, YOSUKE OGATA, Undergraduate Student, YUSUKE IMAI, Graduate Student, and HITOSHI MATSUMOTO, Professor, are with the Department of Materials Science and Engineering; TAKEFUMI GOTO, Graduate Student, and YUKIHIRO YOSHIMURA and TAKAHIRO TAKEKIYO, Doctors, are with the Department of Applied Chemistry; and TAKASHI ARAI, Professor, is with the Department of Applied Physics, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan. Contact e-mail: [email protected] Manuscript submitted February 26, 2010. Article published online June 2, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
alkyl chain length n.[6] On a structural approach, in [C1mim][PF6]-benzene mixtures, the benzene concentration dependence on the packing efficiency was clarified by WANS.[7] The addition of benzene causes a repulsive interaction between cations. On a mesoscopic scale, nanoscale heterogeneities were found in [Cnmim][Cl] (n = 3, 4, 6, 8, and 10) and [Cnmim][BF4] (n = 4, 6, and 8).[8] The systematic wide-angle X-ray scattering (WAXS) data show that the size of heterogeneity is proportional to the alkyl chain length. However, smallangle neutron scattering (SANS) experiments were carried out to examine the molecular aggregation of [C4mim][BF4]-, [C8mim][I]-, and [C8mim][Cl]-H2O mixtures.[9] The molecular aggregation form depends on the H2O concentration. With the MD simulation of [C8mim][NO3]-H2O mixtures, the nanostructural organization also was reported.[10] Anion–water, anion– anion, and water–water interactions varied remarkably depending on the water concentration. By their competing interactions, a microheterogeneity of nonpolar and polar phase separation occurs on nanoscale. N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate and bis (trifluoromethylsulfonyl) imide, [DEME][BF4] and [DEME][TFSI] as different kinds of RTILs are well known to be electric doublelayer capacitors, which have a wide electric potential window.[11] [DEME
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