Low-temperature Liquids Research Articles

Modeling of band shapes in the low-temperature molecular liquid spectra affected by resonance dipole–dipole interaction

The band shape theory of the vibrational transitions accompanied by an excitation of a strongly IR-active fundamental is elaborated for low-temperature molecular liquids with an account for strong intermolecular resonance dipole–dipole interactions. The developed model of a liquid uses the regular (fcc structure) crystal whose structure is then destroyed by introducing random, normally distributed displacements of particle positions, by assigning arbitrary molecular orientations as well as a varied number of randomly distributed vacancies. This model was applied to several molecular liquids ( CF 4 , SiF 4 , SF 6 , CF 3 Cl, and CF 3 Br ) , those having triply degenerate modes were studied more in detail.

Pressure dependence of dynamical heterogeneity in water

Using molecular dynamics simulations we investigate the effect of pressure on the dynamicalheterogeneity in water. We show that the effect of a pressure variation in water is qualitativelydifferent from the effect of a temperature variation on the dynamical heterogeneity in theliquid. We observe a strong decrease of the aggregation of molecules of low mobilitytogether with a decrease of the characteristic time associated with this aggregation.However, the aggregation of the most mobile molecules and the characteristic time of thisaggregation are only slightly affected. In accordance with this result, the non-Gaussianparameter shows an important decrease with pressure while the characteristic timet* of the non-Gaussian parameter is only slightly affected. These results highlight then theimportance of pressure variation investigations in low temperature liquids on approach tothe glass transition.

Differential Capacitance of the Electrical Double Layer in Imidazolium-Based Ionic Liquids: Influence of Potential, Cation Size, and Temperature

The interfaces formed at glassy carbon electrodes in three low-temperature ionic liquids (1-methyl-3-ethylimidazolium chloride, emimCl; 1-methyl-3-butylimidazolium chloride, bmimCl; and 1-methyl-3-hexylimidazolium chloride, hmimCl) were investigated by cyclic voltammetry and impedance spectroscopy. The potential dependence of the differential double layer capacitance was measured at several temperatures between 80 and 140 °C, and the temperature response was found to be broadly similar to that obtained with high-temperature molten salts. The differential capacitance/potential curves have a minimum and two side branches. The minimum corresponds to the point of zero charge. The differential capacitance increases in the order hmimCl < bmimCl < emimCl because the double layer is thinner when imidazolium (Rmim) cations with shorter alkyl chain lengths are used. The impedance spectra and capacitance curves indicate that cations are adsorbed at the open-circuit potential and that their surface excess concentrati...

Direct density determination of low- and high-density glassy polyamorphs following a liquid–liquid phase transition in Y 2O 3–Al 2O 3 supercooled liquids

Evidence has been presented for a density-driven phase transition occurring between supercooled liquids in the system Y 2O 3–Al 2O 3. The high- and low-density liquids were quenched to metastably coexisting glasses. Chemical analysis showed the compositions of the two glasses to be identical, and it was inferred that they differed in their densities and entropies. The entropy difference has been verified by calorimetry. Here, we confirm that the chemical compositions of the glassy materials derived from the high- and low-temperature liquids are identical. We present a direct density determination of the two glasses using sink-float techniques. The measured densities are 3.72(3) g/cm 3 for the glass derived from the high-temperature liquid (i.e., the high-density amorphous or HDA polyamorph), and 3.58(1) g/cm 3 for the low-temperature (low-density, LDA) polyamorph.

Model energy landscapes of low-temperature fluids: Dipolar hard spheres

An analytical model of non-Gaussian energy landscape of low-temperature fluids is developed based on the thermodynamics of the fluid of dipolar hard spheres. The entire excitation profile of the liquid, from the high-temperature liquid to the point of ideal-glass transition, has been obtained from Monte Carlo simulations. The fluid of dipolar hard spheres loses stability close to the point of ideal-glass transition transforming via a first-order transition into a columnar liquid phase of dipolar chains locally arranged in a body-centered-tetragonal order. Significant non-Gaussianity of the energy landscape is responsible for narrowing of the distribution of potential energies and energies of inherent structures with decreasing temperature. We suggest that the proposed functionality of the enumeration function is widely applicable to both polar and nonpolar low-temperature liquids.

Electrochemical activation and dehalogenation of freons in low-temperature ionic liquids

The effect of various factors (the nature of the medium and the electrode material, the electronic structure of the Freons, etc.) on the electrochemical activation and dehalogenation of a series of Freons [F113 (CF2ClCFCl2), F13B1 (CF3Br), F114B2 (CF2BrCF2Br), and F113B2 (CFClBrCF2Br)] in various low-temperature ionic liquids (LTIL) [1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imides and 1-butyl-3-methylimidazolium hexafluorophosphate, tetrafluoroborate, and trifluoroacetate] at various electrodes (glassy carbon, Pt, Ag) was studied. It was established in particular that the investigated processes are affected substantially by the electrical conductivity and viscosity of the medium. With decrease of the latter the peak potential in the cyclic voltammetry of the electrochemical reduction of the Freons is shifted toward less negative values while the current increases. It was found that a silver cathode has a specific effect on the electrochemical activation of the Freons in the LTILs, and this may be due to the formation of complexes Ag⋯Hal⋯Rf between the Freons and silver atoms on the electrode surface, in which cleavage of the C—Hal bond is facilitated. Such processes are compared with the processes realized in the traditional solvent dimethylformamide.

Gravitational capillary viscometer for low-temperature liquids

A pressurized gravitational capillary viscometer was developed for subcooled liquefied gases such as oxygen, nitrogen, hydrogen, and methane. It acquires accurate absolute viscosity measurements with an uncertainty of 1% at a 95.5% confidence level, necessary for the demands of aerospace engineering. The viscometer includes a coiled capillary of electroformed nickel that hydraulically connects two reservoirs located at equal heights. Using helium gas to temporarily drive liquid from a third supply reservoir, a level difference is created between the first two reservoirs without the need to tilt or invert the viscometer. Helium gas is then used to pressurize the first two reservoirs equally. Each reservoir holds a capacitive liquid-level sensor that both measure the flow induced by gravity through the capillary more precisely than by visual observations through windows. Viscosity data for liquid oxygen were acquired in the pressure domain from 0.15 to 1.0 MPa and in the temperature domain from the normal boiling point to near the freezing point. Published viscosity data and correlations for subcooled liquid oxygen are not precise nor complete in this density regime. Accordingly, the viscosity data delivered by the viscometer of the present work are superior.

Kondo, fluctuation valence and non-Fermi liquid behaviors in CeNiSn 1−xGe x (0⩽ x⩽1)

We report on crystalline structure, electrical resistivity, DC and AC magnetic susceptibilities, magnetization and magnetostriction (up to H=30 T and down to 4 K) for the orthorhombic CeNiSn 1− x Ge x compounds. For 0< x⩽0.15 we find low-temperature Kondo ground state (GS), a gap being opened for x=0, crossing over for 1> x⩾0.75 to high-temperature Kondo (from resistivity, ρ) and further to fluctuating valence (FV) (from susceptibility, χ dc) behaviors. Low-temperature Kondo GS reappears for x=1. Kondo antiferromagnet is found for x=0.10, reappearing for x=0.90, although antiferromagnetic two-spin correlations dominate for whole x. Ge-rich compounds ( x=0.95, 0.90) appear as low-temperature non-Fermi liquids ( ρ∼ T), showing also broad maxima of fluctuating valence. Compounds for x=0, 0.1 and 0.9 show valence transitions at temperatures T v; at T v ( H=30 T), volume, ω and tetragonal, λ t magnetostrictions become giant, ω≈10 −2.

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF6, CF4, SiF4, NF3, CHF3, CC1F3, CBrF3, OCS, N2O, and CO2 molecules in the liquid state and in solutions in liquefied Xe, Kr, and O2 are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.

Zn and Cu isotopic variations in chondrites and iron meteorites: Early solar nebula reservoirs and parent-body processes

High-precision Zn isotopic variations are reported for carbonaceous chondrites (CC), equilibrated (EOC) and unequilibrated (UOC) ordinary chondrites, iron meteorites from the IAB-IIICD (nonmagmatic) and IIIA (magmatic) groups, and metal from the Brenham pallasite. For irons, δ 65Cu values are also reported. Data have also been obtained on a coarse-grained type-B calcium-, aluminum-rich refractory inclusion (CAI) from Allende and on acid leaches of Allende (CV3), Krymka (LL3), and Charsonville (H6). Variations expressed as δ 66Zn (deviation in parts per thousand of 66Zn/ 64Zn in samples relative to a standard) spread over a range of 0.3‰ for carbonaceous chondrites, 2‰ for ordinary chondrites, and 4‰ for irons. The measured 66Zn/ 64Zn, 67Zn/ 64Zn, and 68Zn/ 64Zn ratios vary linearly with mass difference and define a common isotope fractionation line with terrestrial samples, which demonstrates that Zn was derived from an initially single homogeneous reservoir. The δ 66Zn values are correlated with meteorite compositions and slightly decrease in the order CI, CM, CV-CO, and to UOC. The isotopically light Zn of Allende CAI and the acid-resistant residues of Allende and Krymka show that the light component is associated with refractory material, presumably minerals from the spinel-group. This, together with the reverse correlation between relative abundances of light Zn isotopes and volatile element abundances, suggests that Zn depletion in planetary bodies with respect to CI cannot be ascribed to devolatilization of CI-like material. These observations rather suggest that refractory material reacted with a gas phase enriched in the lighter Zn isotopes. Alternatively, chondrules with their associated rims should carry a light Zn isotopic signature. The δ 66Zn values of unequilibrated chondrites are rather uniform, whereas equilibrated chondrites show distinctly more isotopic variability. The values of δ 65Cu-δ 66Zn in irons define two trends. The moderate and positively correlated Cu and Zn isotope variations in IIIA and pallasite samples probably reflect crystallization of silicate, sulfide, and solid metal from the liquid metal. The range of δ 66Zn values of the IAB-IIICD group is large (>3‰) and contrasts with the moderate fractionation of Cu isotopes. We interpret this feature and the negative δ 66Zn-δ 65Cu correlation as reflecting mixing, possibly achieved by percolation, between metals from a regolith devolatilized at low temperature (enriched in heavy zinc) and metallic liquids formed within the parent body.

Low-temperature ionic liquids immobilized in porous alumina

The pores in an aluminum oxide matrix can be completely filled with 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, triflates, and bis(trifluoromethylsulfonyl)imides. This possibility can be utilized to produce solid electrolytes for batteries and fuel cells.

可視化法による液体3Heの沸騰観測

The behaviors of bubble nucleation and growth in liquid 3He were investigated visually using the shadowgraph method. We have constructed two types of cryostats and sample cells for measurements between 0.5 and 1K. The 3He bubble that formed on the heated copper surface was spheroid-like due to a low surface tension and small buoyancy force. The time for required for the bubble to grow and separate from the surface was 14ms at a heat flux of q = 8=10-5 W/cm2 and bulk liquid 3He temperature of 0.7K. This means that the bubble growth rate is high as compared to other low-temperature liquids. The bubble size, number of bubbles separating from the heated surface in a specific time and the rising velocity of the bubbles were analyzed using photographs obtained from a high-speed camera as a function of heat flux and liquid 3He temperature. In the region of large heat flux, large bubbles formed by bubble accumulation covered the copper surface and the increase in bubble number as q increased became insignificant. In this region, the amount of heat flux carried by bubbles as latent vaporization heat was approximately 60% of the applied heat flux. The characteristic heat transfer curve of liquid 3He measured previously by our group could be explained qualitatively by these boiling behaviors.

Electroacoustics in low-temperature ionic liquids

Titanium dioxide was used as a model colloid to demonstrate the possibility of obtaining reliable values of the electrophoretic mobility in low-temperature ionic liquids. Mobilities as low as −0.98±0.16×10−10 and −1.25±0.33×10−10m2V−1s−1 were found in dry and wet 1-butyl-3-methylimidazolium triflate, respectively. These values are lower by two orders of magnitude than typical mobilities in stable aqueous dispersions due to a high viscosity of the ionic liquids.

Electroacoustics in low-temperature ionic liquids

Titanium dioxide was used as a model colloid to demonstrate the possibility of obtaining reliable values of the electrophoretic mobility in low-temperature ionic liquids. Mobilities as low as −0.98±0.16×10 −10 and −1.25±0.33×10 −10 m 2 V −1 s −1 were found in dry and wet 1-butyl-3-methylimidazolium triflate, respectively. These values are lower by two orders of magnitude than typical mobilities in stable aqueous dispersions due to a high viscosity of the ionic liquids.

Thermodynamic manifestations of structure fluctuations in liquids.

Fluctuations of pressure and internal energy in a low-temperature liquid, generated by structure fluctuations, are related in a general and straightforward way to the differences between the long- and short-time thermodynamic susceptibilities. The relations are similar to, but not identical with, those between thermodynamic fluctuations and susceptibilities in classical statistical mechanics. The derivation is general and straightforward, and based on the assumption that the local structure is a slow-relaxing mode in low-temperature liquids and may be characterized by an order parameter.

Review: Current studies on some physical properties of ionic liquids

As a novel substituting solvent for organic solvents, low-temperature ionic liquids have attracted much attention as good media in organic synthesis and other chemical processes. Better understanding of physical properties of ionic liquids are very helpful in exploring reaction mechanisms and controlling reaction outputs. This review summarises current studies on several physical properties (melting point, vapor pressure and stability, polarity, miscibility, density, viscosity) that are important for organic reactions.

Spreading of Liquid Ag and Ag–Mo Alloys on Molybdenum Substrates

Abstract The spreading of liquid Ag and Ag–Mo alloys on molybdenum substrates has been studied, using a drop-transfer setup. Even though initial spreading velocities as fast as ≈ 1 m/s have been recorded in some experiments, a large variation in the spreading dynamics has been observed, and there is no unique relationship between the contact angle and the spreading velocity. This can be attributed to the formation of ridges at the triple junction, the movement of which controls spreading. The fastest spreading rates are consistent with results reported for low-temperature liquids; these can be described, using a molecular-kinetic model. Spreading kinetics and final contact angles were similar for pure Ag and Ag–Mo liquids.

Investigation of the Stability of Low-Temperature Ionic Liquids with High-Activity Anodes

Investigation of the Stability of Low-Temperature Ionic Liquids with High-Activity Anodes

Phase Relationships and Phase Formation in the System BaF2-BaO-Y2O3-CuOx-H2O

ABSTRACTThe interplay of melting equilibria and reaction kinetics is important during formation of the Ba2YCu3O6+x (Y-213) phase from starting materials in the quaternary reciprocal system Ba,Y,Cu//O,F. For experimental investigation of the process we used a combination of differential thermal analysis (DTA) for study of melting equilibria, and in-situ high-temperature x-ray diffraction (HTXRD) for study of the phase formation and reaction kinetics. DTA investigation of compositions spaced along compositional vectors extending from the oxide end to the fluoride end of the reciprocal system have given evidence of low melting liquids (∼600 °C) near the fluorine-rich end. Work is continuing to determine whether similar thermal events observed in the interior of the system also indicate low temperature liquids, and on the extent to which low-melting liquids could be involved in Y-213 phase formation. HTXRD investigations have been initiated on the conversion of 0.3 μm and 1.0 μm thick BaF2-Y-Cu precursor films to Y-213 in the presence of water vapor. Preliminary results indicated that the thickness of film has a strong influence on the texture of the Y-213 film: a 0.3 μm film showed mainly (001) texture, whereas a 1.0 μm film showed a greater volume fraction of (h00) texture. While the HTXRD method cannot directly reveal the presence of liquid, we are working to combine DTA and HTXRD data for a unified picture of Y-213 phase formation during the “BaF2 ex-situ” process for coated-conductor fabrication.

A Method for Studying the Structure of Low-Temperature Ionic Liquids by XAFS

An in situ method of studying the structure of reactive ionic materials in the solid and liquid states by XAFS is described. These salts have novel catalytic and solvent properties, and the results show that their structure may be studied using transmission XAFS by utilizing pressed disks of BN, graphite, and LiF and is not affected by the sample matrix used.