Phase behavior of three-component ionic fluids

We study the phase behavior of solutions consisting of positive and negative ions of valence z to which a third ionic species of valence Z>z is added. Using a discretized Debye-Hückel theory, we analyze the phase behavior of such systems for different values of the ratio . We find, for , a three-phase coexistence region and, for , a closed (reentrant) coexistence loop at high temperatures. We characterize the behavior of these ternary ionic mixtures as function of charge asymmetry and temperature, and show the complete phase diagrams for the experimentally relevant cases of and , corresponding to addition of divalent and trivalent ions to monovalent ionic fluids, respectively. Received 6 April 2000 and Received in final form 20 July 2000     

Phase behaviors of ionic liquids attributed to the dual ionic and organic nature

Ionic liquids (ILs), also known as room-temperature molten salts, are solely composed of ions with melting points usually below 100 °C. Because of their low volatility and vast amounts of species, ILs can serve as ‘green solvents' and ‘designer solvents' to meet the requirements of various applications by fine-tuning their molecular structures. A good understanding of the phase behaviors of ILs is certainly fundamentally important in terms of their wide applications. This review intends to summarize the major conclusions so far drawn on phase behaviors of ILs by computational, theoretical, and experimental studies, illustrating the intrinsic relationship between their dual ionic and organic nature and the crystalline phases, nanoscale segregation liquid phase, IL crystal phases, as well as phase behaviors of their mixture with small organic molecules.     

Phase separation of highly dissymmetric binary ionic mixtures

We study the phase separation of binary ionic mixtures involving two species of classical point ions in a rigid uniform neutralizing background of degenerate electrons. The thermodynamic properties of the ionic fluid are calculated on the basis of the HNC integral equation for the three partial pair distribution functions. We develop a systematic technique which allows the properties of mixtures of arbitrary composition to be expressed in terms of infinitely dilute solutions. Phase diagrams and critical parameters are determined for 12 different binary systems involving ionic charge ratios between 2 and 8. The dependence of the critical temperature on the ionic charges, on the pressure and an ionic quantum corrections is examined in detail.     

Phase behavior of hard particles

The phase behavior of hard particles and mixtures thereof is reviewed. Special attention is given to a lattice model consisting of hard hexagons and points on a triangular lattice. This model appears to have two disordered phases and an ordered phase.     

Phase behavior of organic-inorganic crystal

We have investigated the structure and phase behavior of nonmolecularly layered silver stearate by means of temperature-dependent diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Upon heating the sample, remarkable spectral changes took place. The first phase transition took place that might be associated with a premelting event characterized by the formation of gauche conformers at 390-420 K. A second phase transition took place in which silver nanoparticles with a size of ∼4 nm were formed by thermal decomposition of silver stearate at 520-550 K. These silver nanoparticles, derivatized by stearate, were readily spread as a monolayer at air/water interface, and could be packed in 3-D assemblies by the Langmuir-Blodgett method. Received 29 November 2000     

Phase behavior of methane haze

Methane aerosols play a fundamental role in the atmospheres of Neptune, Uranus, and Saturn's moon Titan as borne out by the recent Cassini-Huygens mission. Here we present the first study of the phase behavior of free methane aerosol particles combining collisional cooling with rapid-scan infrared spectroscopy in situ. We find fast (within minutes) phase transitions to crystalline states directly after particle formation and characteristic surface effects for nanometer-sized particles. From our results, we conclude that in atmospheric clouds solid methane particles are crystalline.     

一维扩展离子Hubbard模型的相图研究

应用密度矩阵重整化群方法, 研究了存在交错离子势Δ时一维半满扩展Hubbard模型的相图. 通过计算关联函数、结构因子、位置算符等方法, 描绘了从Mott绝缘体-键有序绝缘体-Band 绝缘体的特性并给出了精确的相边界. 研究发现: 中间的键有序绝缘体相在相图中占据了很小的一部分区域, 当存在离子势Δ的情况下, 这个区域将会有所增大; 而当相互作用足够强时, 这个中间相消失. 给出了离子Hubbard模型(最近邻电子-电子相互作用V=0)的相图.     

Phase behavior of DODAB aqueous solution

Phase behavior of DODAB aqueous solution, prepared without sonication, was studied by adiabatic scanning calorimetry. Measurements revealed four phase transitions with the temperatures 35.2, 39.6, 44.6, and 52.4°C at heating and one transition at the temperature 40.4°C at cooling. The first three transitions at heating occur in unilamellar vesicles. The first and third transitions correspond to the subgel-gel and gelliquid phase transitions, corresponding enthalpy jumps are equal to 33 and 49 kJ/mol. The second transition appears after some aging and is similar to gel-ripple phase transition in a DPPC solution, with the enthalpy jump under the transition exceeding 7.4 kJ/mol. The transition occurs in unilamellar vesicles. The transition at the temperature 52.4°C occurs in another subsystem of the solution, which we believe to be multilamellar vesicles. The enthalpy jump at this transition is equal to 97 kJ/mol, and data analysis suggests that this is a subgel-liquid transition. The phase transition at cooling is the liquid-gel transition in unilamellar vesicles. During the measurements, a slow evolution of the solution occurs, consisting in a change of concentrations of unilamellar and multilamellar vesicles. This transformation mainly occurs at low temperatures.     

Phase behavior of columnar DNA assemblies

The interaction between two stiff parallel DNA molecules depends not only on the distance between their axes but also on their azimuthal orientation. The positional and orientational order in columnar B-DNA assemblies in solution is investigated, on the basis of the electrostatic pair potential that takes into account DNA helical symmetry and the amount and distribution of adsorbed counterions. A phase diagram obtained by lattice sums predicts a variety of positionally and azimuthally ordered phases and bundling transitions strongly depending on the counterion adsorption patterns.     

Crossover behavior of anisotropic cubic system with ionic anisotropy

Crossover behavior of anisotropic cubic N-component spin system with ionic anisotropies of different magnitude is studied in terms of the renormalization-group (RG) approach in momentum space. As a fundamental case, we choose a system with two kinds of strength of ionic anisotropies (i.e. m²₁ for the M-component spin and m²₂ for the other (N–M)-one), which has a bicritical point. We discuss the critical behavior and crossover behavior between the M- component system and the N-component system on the critical exponents [i.e., coefficient functions appearing in the RG equation of γS for the spin field S, γS² for the S²-field and γδS² for the δS² (≡[(N-M)S²₂-MS²₂]/N)-field] and on the temperature-dependent crossover exponent γeff.     

Phase transition of ice precipitated in an aqueous ionic glassy matrix

In an easily forming glass aqueous electrolyte, an ice precipitation appears, that is variable with water to salt mole-ratio R. We here describe the 1 _c → 1 _h phase transition. The initial conditions of these transitions are small crystallites, a condensed form of water, with size varying from clusters to 250 Å. The transition to 1 _h can be considered as healing of the 1_h faults, which is accompanied by an apparent weakening of the cubic structure due to symmetry loss. Order parameter and specific effects, such as branching, are postulated in this growth which appears as a random walk in an ultrametric space.     

Phase behavior of thermally responsive microgel colloids

The phase behavior of poly-N-isopropylacrylamide (PNIPAM) nanoparticles dispersed in water is investigated using a thermodynamic perturbation theory combined with light-scattering and spectrometer measurements. It is shown how the volume transition of PNIPAM particles affects the interaction potential and determines a novel phase diagram that has not been observed in conventional colloids. Because both particle size and attractive potential depend on temperature, PNIPAM aqueous dispersion exhibits phase transitions at a fixed particle number density by either increasing or decreasing temperature.     

Phase behavior and nucleation kinetics of Octaphenylcyclotetrasiloxane

Phase behaviour and certain aspects of phase-transformation kinetics for Octaphenylcyclotetrasiloxane (OPCTS) have been determined by means of differential scanning calorimetry and optical microscopy. Three solid phases have been observed: 3 (stable at room temperature), 2 (stable above 76.6°C), and 1 (stable above 189.5°C). The 3-and 2-phases are optically anisotropic and mechanically brittle; the 1-phase is optically isotropic and soft or plastic. Although the 3-phase is thermodynamically unstable above 76.6°C, its transformation to the 2-phase is sufficiently slow that the 3 → 1 transition can be studied. The transition temperatures (and corresponding latent heats) for the 3 → 2, 3 → 1, 2 → 1, and melting transitions are: 76.6°C (～2.9 KJ/mol), 186.0°C (47.3 KJ/mol), 189.6°C (43.76 KJ/mol), and 204.9°C (1.95 KJ/mol). The entropy of melting (ΔS_m = 0.491 R) is one of the lowest measured for any solid. The low-melting entropy, isotropy, and plasticity of the 1-phase lead to the conclusion that it is an orientationally-disordered crystal mesophase (plastic crystal).

The kinetic behavior of the 3 → 2 phase transformation, as determined by DSC, supports a theoretical model taking homogenous nucleation as the rate-determining process.     

Anomalous dielectric behavior of water in ionic newton black films

The electrostatics of two charged surfactant layers in aqueous media (surfactant/water/surfactant films) is investigated using molecular dynamics simulations. In the films studied (with a surfactant-surfactant distance from approximately 35 A to contact) we observe an anomalous dielectric response of water. The electrostatic potential phi(z) inside the aqueous core of the films (containing bulk water with rho=1 g/cm(3)) is completely different from that expected for a film containing a dielectric medium with the dielectric constant of water. In addition, our results are not consistent with a local relation between the water polarization P(z)(z) and the electric field E(z)(z). The polarization P(z)(z) is maximum at the interfaces (due to solvent molecules forming part of the structure of the surfactant layers) and decays from the interfaces inside the aqueous core with a decay length of order of approximately 10 A.     

Mesophilic alcohol dehydrogenase behavior in imidazolium based ionic liquids

The use of ionic liquids to replace organic solvents in biocatalytic processes has recently gained much attention. Despite the wide applications of oxidoreductases, there are few reports of their catalyzed reaction in ionic liquid. We have investigated the influence of four water miscible ionic liquids on the activity, stability and structure of the mesophilic alcohol dehydrogenase from yeast. Upon changes in ionic liquids concentration, both activity and stability of the enzyme were affected. As the concentration of ionic liquids increased, K_m increased while k_cat decreased. Associated conformational changes caused by ILs (150 mM) were monitored using fluorescence technique. Finally, the effects of ILs cations and anions on the enzyme activity and stability in aqueous IL mixtures were discussed.     

Changes in dynamical behavior of ionic liquid in silica nano-pores

Dielectric relaxation measurement has been carried out on an ionic liquid (1-butyl-3-methyl imidazolium hexafluorophosphate, [BMIM][PF₆]) confined in nano-porous silica matrix. Two dielectric relaxation peaks have been observed in the confined ionic liquid (IL) while there is only one relaxation peak for bulk IL. Confinement results in layering of some IL molecules near the pore wall while other molecules, less affected by pore wall interaction, remain in the central core. The two relaxation peaks are assigned to the different dynamical behaviors of the central core and layered IL molecules.     

High ionic conductive behavior of cyanoethylated polyvinylalcohol- and polyacrylonitrile-based electrolytes

New type polymer electrolyte films based on poly(acrylonitrile), (PAN), and cyanoethylated poly(vinyl alcohol), (CN-PVA), were prepared and their conducting behaviors were investigated. CN-PVA was prepared from poly(vinyl alcohol), (PVA) and acrylonitrile in the presence of sodium hydroxide and quaternary ammonium halide as a phase transfer catalyst. Free standing PAN- and CN-PVA-based electrolyte films were prepared by casting the propylene carbonate (PC) solution containing PAN, CN-PVA and LiClO₄ and removing some amount of PC. Ionic conductivity of the electrolyte film, (PAN)10(CN-PVA) 10(LiClO₄)8(PC)4 composite film was 14.6 mS cm^− 1 at 30 °C and 22.4 mS cm^− 1 at 60 °C. FTIR results for the electrolyte films suggest that the nitrile groups in the CN-PVA matrix mainly interact with the lithium ions in the films and enhance dissolution of the lithium salt in the electrolyte films.