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Phase transition is observed between one-phase disordered phase and an ordered phase with multilamellar (onion) structures in an off-critical mixture of D2O and 3-methylpyridine (3MP) containing a salt at 85mM. The salt consists of hydrophilic cations and hydrophobic anions, which interact asymmetrically with the solvent composition fluctuations inducing mesophases. The structure factor of the composition distribution obtained from small-angle neutron scattering has a peak at an intermediate wave number in the disordered phase and multiple peaks in the ordered phase. Lamellar layers forming onions are composed of solvation-induced charged membranes swollen by D2O. The onion phase is realized only for small volume fractions of 3MP (in D2O-rich solvent).PACS numbers: 82.45. Gj, 61.20.Qg, 64.75.Cd, 81.16.Dn Binary mixtures of water and organic solvent have been used extensively to study universal aspects of critical behavior and phase separation dynamics. However, not enough attention has yet been paid to unique ion effects in such mixtures, where preferential hydration around each ion should affect the composition fluctuations [1,2]. Salts composed of small hydrophilic ions can drastically change the phase behavior even at small concentrations [3,4,5,6,7]. More strikingly, many groups have observed long-lived heterogeneities (sometimes extending over a few micrometers) in one-phase state [8,9] and a third phase visible as a thin plate formed at a liquid-liquid interface in two-phase state [10]. These observations were reproduced in different experiments using solvents and salts of high purity, so they should be regarded as ioninduced supramolecular aggregates. We also comment on a mixture of water+isobutylic acid (IA), where IA partly dissociates into H + and Butyrate − ions. There, the mobility of H + ions much decreases at large IA contents in one-phase state [11] and the third phase also appears around an interface in two-phase state [10]. Similar phenomena have often been observed in various soft matters such as polymers, gels, colloids, and mixtures containing surfactants. Though not well understood, the solvation (ion-dipole) interaction among ions and polar molecules should play a major role in these phenomena together with the Coulombic interaction among charges. [1,2] Recently, the solvation effect on phase behavior was * Electronic address: hideki.seto@kek.jp theoretically studied in polar mixtures including the case of antagonistic ion pairs composed of hydrophilic and hydrophobic ions [12]. Such cations and anions interact differently with the composition fluctuations, leading to a charge-density-wave phase for sufficiently large solvation asymmetry even at small salt concentrations. In a smallangle neutron scattering (SANS) experiment, Sadakane et al. [13] found a peak at an intermediate wave number Q m (∼ 0.1Å −1 ) in a near-critical mixture of D 2 O and 3-methylpyridine (3MP) containing sodium tetraphenylborate NaBPh 4 at 100 mM. The volume fraction of 3MP, denoted by φ 3MP , was chosen to be 0.3...

The structure and dynamics of a ternary system composed of deuterium oxide (D2O), 3-methylpyridine (3MP), and sodium tetraphenylborate (NaBPh4) are investigated by means of small-angle neutron scattering (SANS) and neutron spin echo (NSE) techniques. In the SANS experiments, a structural phase transition is confirmed between a disordered-phase and an ordered-lamellar-phase upon variation of the composition and/or temperature of the mixture. The characteristic lengths of the structures is on the sub-micrometer scale. A dispersion relation of the structure is measured through NSE experiments, which shows that the relaxation rate follows a cubic relation with momentum transfer. This implies that the dynamics of the system are determined predominantly by membrane fluctuations. The present results indicate that 3MP-rich domains are microscopically separated from bulk water in the presence of NaBPh4, and that the layers behave as membranes. These results are interpreted that preferential solvation of salt in each solvent induces a microphase separation between the solvents, and the periodic structure of 3MP-rich domains is stabilized by the long-range electrostatic interaction arising from Na(+) ions in D2O-rich domains.

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The phase transition behavior and dynamics of ionic liquid crystals, 1-methyl-3-alkylimidazolium tetrafluoroborate with various alkyl chain lengths, were investigated by X-ray scattering, differential scanning calorimetry, optical microscopy, and dielectric relaxation spectroscopy to elucidate the mechanism of their structural and phase changes. A metastable phase was found to appear via a supercooled smectic phase on cooling. In the metastable phase, disorder in the smectic phase is partially frozen; thus, the phase has order higher than that of the smectic phase but lower than that of the crystalline phase. During the subsequent heating process, the frozen disorder activates, and a crystalline phase appears in the supercooled smectic phase before entering the smectic phase. The relationship between the phase behavior and the dynamics of charge carriers such as ions is also discussed.

The hydrogen bonds of the imidazolium-ring H atoms of ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amides ([Cnmim][TFSA], n = 2 to 12 where n represents the alkyl chain length), with the O atom of dimethyl sulfoxide (DMSO) have been elucidated using 1H, 13C, and 15N NMR spectroscopy and soft X-ray absorption and emission spectroscopy (XAS and XES). Density functional theory (DFT) calculations have been performed on an isolated DMSO molecule and two cluster models of [Cnmim]+-DMSO by hydrogen bonding to interpret the XES spectra for the [Cnmim][TFSA]-DMSO solutions. The 1H and 13C NMR chemical shifts of the imidazolium ring showed that deshielding of the ring H and C atoms is moderate as the DMSO mole fraction xDMSO increases to ∼0.8; however, it becomes more significant with further increase of xDMSO. This finding suggests that the hydrogen bonds of the three ring H atoms with the DMSO O atoms are saturated in solutions with xDMSO increased to ∼0.8. The 1H and 13C chemical shifts of the alkyl chains revealed that the electron densities of the chain H and C atoms gradually decrease with increasing xDMSO, except for the N1-bound carbon atom C7 of the chain. The 15N NMR chemical shifts showed that the imidazolium-ring N1 atom which is bound to the alkyl chain is shielded with increasing xDMSO in the range from 0 to 0.8 and is then deshielded with further increase of xDMSO. In contrast, the imidazolium ring N3 atom is simply deshielded with increasing xDMSO. Thus, the electron densities of the alkyl chain may be condensed at the C7 and N1 atoms of [Cnmim]+ by the hydrogen bonding of the ring H atoms with DMSO. The hydrogen bonding of DMSO with the ring results in low-energy shifts of the XES peaks of the O K-edge of DMSO. Small-angle neutron scattering experiments showed that [Cnmim][TFSA] and DMSO are homogeneously mixed with each other on the mesoscopic scale. This results from the strong hydrogen bonds of DMSO with the imidazolium-ring H atoms.

Liquid–liquid phase separation of binary systems for imidazolium-based ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI], n represents the alkyl chain length of the cation) with 1,4-dioxane (1,4-DIO) has been observed as...