Quantum conductance of monatomic Ni nanobridges

The quantum conductance phenomena in narrow metal nanobridges were investigated. The nanobridge devices with small atomic-wide gap were formed by a novel controlled electroplating method on a nanolithographed quartz wafer. The metallic contact nanowires were grown across the gap by field evaporation. The field-induced formation and field-stabilization of monatomic Ni nanobridges are described. Thus formed Ni nanowires appeared to be unstable in the absence of electric field and disassembled quickly under no field conditions. The minimum quantum conductance associated with monatomic constriction in the nanobridge was observed. Exceptionally stable monatomic quantum nanobridges (QNB) were obtained by chemical treatment. They were investigated in the dry state and in the electrolyte solutions. The quantum conductance with zero temperature coefficient was observed at low electric field strength E (bias voltage |V_b| < 0.3 V) but thermionic conductance dominated at higher E (|V_b| > 0.8 V) leading to the conductance increase with temperature, opposite to the behavior of a bulk Ni metal. The mechanism of the observed phenomenon is presented. To gain further insights into the thermionic barrier formation in QNB, we have performed quantum mechanical calculations, using semi-empirical method, for model Ni nanobridge atom clusters (base:nanowire:base = 6:n:6 atoms, with n = 1-5). They have shown that in longer joining nanowires (n > 1) the lowest unoccupied molecular orbitals (LUMO) are predominantly concentrated over base electrodes (reservoirs) rather than over the nanowire constriction, while the short (monatomic) nanowires are densely populated with low lying LUMO's. The results of calculations suggest also that the location of the quantum confinement (the constriction) may not necessarily be at the nanowire center (as generally assumed) but rather at the joints of nanowire with base electrodes where the wire width is the lowest.     

Superelectrophilic solvation

Nucleophilic solvation is the interaction of electron-donor solvents with electron-deficient reagents. Electrophilic solvation is the related reverse interaction. Superelectrophilic solvation involves the interaction of electron-donating groups (ligands) of overall electron-deficient species (electrophiles) with strongly electron-acceptor superacids. It occurs with liquid superacids, on solid acids, and even in some enzymatic biological systems. Diminishing neighboring group participation of the electrophilic centers by the affected groups greatly enhances their electrophilic reactivities (superelectrophilic activation), resulting in unusual reactions of substantial interest. Representative examples of superelectrophilic solvation are discussed.     

Analysis of solvation in ionic liquids using a new linear solvation energy relationship

A new linear solvation energy relationship (LSER) equation, where the solute internal energy term has been incorporated into the traditional LSER equation, is used for the analysis of solvation in ionic liquids. Modeling results obtained using the new LSER equation indicate that all solute parameters (dispersion, polarity, hydrogen bonding, cavity formation, and solute internal energy) have approximately equal importance in the solvation of organic solutes in ionic liquids. The magnitude of dispersion interaction is stronger in ionic liquids than in aqueous solution, whereas hydrogen‐bonding interactions are stronger in water than in ionic liquids. This indicates that the solubility of polar compounds that contain bulky and aromatic groups can be enhanced in ionic liquids due to higher dispersion interactions in ionic liquids than in aqueous solution. On the other hand, the LSER equation without the solute internal energy term does not yield the meaningful solute–solvent interaction terms, indicating that the inclusion of a solute internal energy term is necessary to properly describe the solvation of organic solutes in liquid solvents. Copyright © 2004 Society of Chemical Industry     

Tuning the electronic and optical properties of monatomic carbon chains

The electronic, mechanical and optical properties of the monatomic carbon chains recently fabricated are investigated by hybrid density functional calculations. It is shown that the chain owns a direct band gap of 2.21 eV and the ultimate strength of 12.2 nN, which are in good agreements with experiments. The light absorption shows only one sharp peak in a wide photonic energy range up to 10 eV and exhibits a strong anisotropic feature as the absorption of the visible light polarized along the chain axis is five orders of magnitude stronger than that of the light polarized perpendicularly to the chain. By applying elastic strains on the chain, the band gap can be continuously changed from 1.58 to 3.86 eV with the absorption peak shifting correspondingly. Then a realistic graphene-chain device is proposed and is verified to be capable of applying strains up to 9% on the chain, suggesting potential applications in nano-size electro-optical and polarization devices with tunable working wavelengths from 345 to 561 nm.     

A one-dimensional extremely covalent material: monatomic carbon linear chain

Polyyne and cumulene of infinite length as the typical covalent one-dimensional (1D) monatomic linear chains of carbon have been demonstrated to be metallic and semiconductor (Eg = 1.859 eV), respectively, by first-principles calculations. Comparing with single-walled carbon nanotubes, the densities are evidently low and the thermodynamic properties are similar below room temperature but much different at the high temperature range. Polyyne possesses a Young's modulus as high as 1.304 TPa, which means it is even much stiffer than carbon nanotubes and to be the superlative strong 1D material along the axial direction. The Young's modulus of cumulene is estimated to be 760.78 GPa. In addition, polyyne is predicted to be as a one-dimensional electronic material with very high mobility.     

The solvation of cellulose by the action of nitrogen tetroxide in organic solvents

This article reviews the solvation of cellulose by the action of N₂O₄ in presence of a suitable proton acceptor and its subsequent regeneration. The mechanism of the nitrosation reaction and the factors affecting cellulose degradation during solvation and regeneration are discussed. The possible industrial applications of this process as well as the use of cellulose nitrite in the preparation of novel cellulose derivatives are also included.     

Slow solvation dynamics of a water-nitrobenzene system

Very slow changes in solvation taking place in water-saturated nitrobenzene have been observed and studied by nuclear magnetic resonance (NMR), Fourier transform infrared, and inelastic neutron scattering spectroscopy. These changes are most likely caused by the rearrangement of the hydrogen-bonded water network. Lithium salts used as the "reporter" species in the (7)Li NMR experiments accelerate this reorganization. Results of this work are important for electrochemical studies of the nitrobenzene-water interface.     

Structure and solvation in ionic liquids

This Account describes experimental data used to understand the structure of ionic liquids and solute-solvent interactions of both molecular solutes and dissolved metal complexes. In general, the structures of the ionic liquids determined from experimental data show good agreement with both simulated structures and solid-state structures. For all ionic liquids studied, strong charge ordering is found leading to long-range order even in the presence of a solute. For dissolved metal complexes, the ionic liquid is not innocent and a clear dependence on the speciation is observed with variations in both the cation and anion.     

The sorption of ions by polyamides

An analysis is given of the principal thermodynamic factors that influence the distribution of an ion between a macroscopically homogeneous polymer phase and a second homogeneous phase and a general method is proposed for the computation of the equilibrium ion sorptions in well-defined model systems. Particular attention is paid to the sorption of ions by polymers containing ionizable groups and the method is used to clarify some of the current problems in the theoretical explanation of the mechanism of sorption of acid dye anions by polyamide fibers. The method is applicable in principle to any dyeing system in which the fiber phase may be regarded at equilibrium as a macroscopically homogeneous, equipotential volume.     

A universal approach to solvation modeling

Continuum mean-field models that have been carefully designed to address the various electrostatic and nonelectrostatic interactions that develop between a molecule and a surrounding medium are particularly efficient tools for studying the effects of condensed phases on molecular structure, energetics, properties, spectra, interaction potentials, and dynamics. The SM8 model may be combined with density functional theory or Hartree-Fock theory to describe a solute's electronic structure and its self-consistent-field polarization by a solvent. A key feature is the use of class IV charge models to obtain accurate charge distributions (either in the vapor phase or in solution), even when using small basis sets that are affordable for large systems. A second key feature is that nonelectrostatic effects due to cavity formation, dispersion interactions, and changes in solvent structure are included in terms of empirical atomic surface tensions that depend on geometry but do not require atom-type assignments by the user. Use of an analytic surface area algorithm provides very stable energy gradients that allow geometry optimization in solution. The SM8 continuum model, the culmination of a series of SMx models (x = 1-8), permits the modeling of such diverse media as aqueous and organic solvents, soils, lipid bilayers, and air-water interfaces. In addition to predicting accurate transfer free energies between gaseous and condensed phases or between two different condensed phases, SMx models have been useful for predicting the significant influence of condensed phases on processes associated with a change in molecular charge, including acid/base equilibria and oxidation/reduction processes. In this Account, we provide an overview of the algorithms associated with the computation of free energies of solvation in the SM8 model. We also compare the accuracies of the SM8 model with those of other continuum solvation models. Finally, we highlight applications of the SM8 models to compute ionic solvation free energies, oxidation and reduction potentials, and pK(a) values.     

镁-氯溶剂化结构在镁基电解液中的作用

因兼顾成本低、安全性能好及体积能量密度高（3832 A·h·L^-1）等优点,镁金属二次电池受到了广泛关注。但是,镁负极的实际应用仍然受限于电解液活性物种溶剂化结构的认识不足。目前,镁基电解液主要分为醚类溶剂的格氏试剂电解液、氯化镁铝络合物（MACC）电解液和Mg（TFSI）₂基电解液等。其中,镁离子-氯离子的配位结构对镁电池正常运行起到了关键作用,主要突出在降低沉积过电位、增强镁沉积动力学和提高沉积镁可逆性等方面。以氯离子在体相电解液中和在电极界面上与镁之间的相互作用为切入点,分析了镁基电解液的前期开发路线及设计理念,并对镁二次电池的未来发展进行了总结和展望。     

The adsorption of mercuric ions by chitosan

The adsorption of mercuric ions by chitosan was investigated. The study of the adsorption kinetics shows that the rate of adsorption of mercuric ions on chitosan can be interpreted in terms of intraparticle diffusion as the rate-limiting step. The experimental data of adsorption equilibrium from mercuric chloride solutions correlate well with the Langmuir isotherm equation, although at high-solute concentrations, a multilayer type of adsorption with the subsequent increase in the uptake is observed. Column experiment confirms the ability of chitosan for the removal of mercuric ions from solutions in the absence of a high concentration of chlorides.     

Initial solvation of coal with tetralin under liquefaction conditions

Secondary vitroplast, produced by treating a Liddell vitrinite concentrate with tetralin in a continuous flow, packed-bed microreactor under a nitrogen pressure of 13.8 MPa at 360, 410 and 460 °C, has been analysed by i.r. spectroscopy, gel permeation chromatography, solid state ¹³C n.m.r. and reflectance microscopy. Results showed that this intermediate in the liquefaction process had the same carbon aromaticity as the untreated vitrinite concentrate and that both its aromaticity and reflectance were independent of the temperature of formation. It was concluded that the initial solution of the vitrinite concentrate in tetralin involved no significant hydrogenation of the vitrinite.     

Selective solvation of polystyrene in tetralin/cyclohexane mixtures

Refractive index increments and density increments have been measured at 307.6K for polystyrene in binary solvents of 1,2,3,4-tetrahydronaphthalene (tetralin, TET) and cyclohexane over the whole range of solvent composition. Comparison of these increments with the corresponding values obtained at dialysis equilibrium (i.e. at constant chemical potential of low molecular weight species) yielded the coefficients of selective adsorption (γ₁) of TET by the polymer. Positive values of γ₁ were exhibited at solvent compositions up to 78% (v/v) of the thermodynamically better solvent, TET. Theoretical curves of γ₁ vs. composition were calculated on the basis of, firstly, relevant interaction parameters and, secondly, interaction parameters in conjunction with solubility parameters. Both procedures afforded self-consistent results, which were, however, uniformly lower than the experimental values of γ₁.     

Equilibrium swelling and solvation studies on crosslinked polyacrylamides

Polyacrylamide (PA) crosslinked with four different crosslinking agents, triethyleneglycol dimethacrylate (TEGDMA), N,N′‐methylene bisacrylamide (NNMBA), hexanediol dimethacrylate (HDDMA) and divinylbenzene (DVB), with mole percents ranging from 5 to 20, was prepared by solution polymerization and subjected to swelling and solvation studies. Solubility parameters and cohesive energy density were determined from swelling studies. Molecular weight between crosslinks for these systems were determined by Flory–Rehner analysis. There is a discontinuous volume change for 10% NNMBA and HDDMA crosslinked PA, 15% TEGDMA crosslinked PA and 10 and 15% DVB crosslinked PA in solvent mixtures of acetic acid and water due to phase change occurring at this stage. The hydrogels exhibit inhomogeneous crosslink distribution due to multiple crosslinking, cyclization and network irregularity owing from arising from entanglements. As the percentage of crosslinking increases, crosslinks become more homogeneous due to a decrease in entanglements. Copyright © 2004 Society of Chemical Industry     

Ion solvation studied by NMR and electrochemical methods

Electrochemical and NMR experiments with solutions of silver salts in mixtures of water—acetonitrile, water—dimethylsulphoxide, and methanol—dimethylsulphoxide have been compared and discussed in terms of ion solvation and solvent-solvent interactions. The solvation of aluminum(III) in mixtures of N,N-dimethylformamide, dimethylsulphoxide, and nitromethane depends also on solvent-solvent interactions, as ¹H- and ²⁷Al-NMR measurements show.     

强碱离子对MDEA溶剂的影响及对策

针对气体净化厂使用甲基二乙醇胺(MDEA)溶液在脱除气体中CO_2和H_2S的过程中产品质量不合格的问题,分析MDEA溶液中污染物的组成和来源,研究影响MDEA溶液再生效率不高的的主要因素,初步研究了用其它化学方法消除强阳离子影响的方法。     

The mobility of oxygen ions in CaF2

The a.c. conductivity of CaF₂ samples containing a fine dispersion of CaO particles has been measured in the temperature range 630 to 1100 K. The conductivity of the dispersed solid electrolyte is two orders of magnitude higher than that for pure polycrystalline CaF₂ in the middle of the temperature range. Transport measurements on pure single crystals of CaF₂ and polycrystalline samples, with and without CaO dispersion, using Fe+FeO and pure Fe as electrodes, clearly indicate that fluorine ions are the only migrating ionic species with a transport number of almost unity, contrary to the suggestion of Chou and Rapp [1, 2]. The enhanced conductivity of the dispersed solid electrolyte probably arises from two effects. A small solubility of oxygen in CaF₂ results in an increase in the fluorine vacancy concentration and conductivity. Adsorption of fluorine ions on the surface of the dispersed particles of CaO results in a space charge region around each particle with enhanced conductivity. Measurements on a galvanic cell incorporating CaF₂ as the solid electrolyte and oxide electrodes show that the e.m.f. is a function of the activity of CaO at the electrode/electrolyte interface. The response to an oxygen potential gradient is, therefore, through an exchange reaction, which establishes an equivalent fluorine potential at the electrode/electrolyte interface.