Structure of alkali metal ionic clusters

Quantum mechanical calculations show that alkali metal ionic clusters of the type M³⁺₄ have the tetrahedral structure, the stability varying as Na³⁺₄ > K³⁺₄ > Rb³⁺₄. Raman spectroscopy has been employed to establish the tetrahedral structure of Na³⁺₄.     

Effect of alkali metal salts on decomposition of ionic liquid like organic salt

N ¹,N ¹,N ²,N ²-tetramethylethane-1,2-diamine-based ionic salts (TMEDA), N ¹,N ¹,N ¹,N ²,N ²,N ²-hexamethylethane-1,2-diaminium dicyanamide (HMEDA-(DCA)₂) were prepared following the quaternization and subsequent ion exchange. The chemical structure of the HMEDA-(DCA)₂ was confirmed using ¹³C NMR spectrum and elemental analysis. The corresponding viscosity of its 60 wt% solution was found to be lower than 5 cP at room temperature, which was critical for propellant application. The ignition delay of 40 wt% HMEDA-(DCA)₂ solution was decreased to 20–30 ms dramatically using alkali metal salts, Li(CH₃COO), Mg(CH₃COO)₂, and Ca(CH₃COO)₂ as a co-catalyst when white fume nitric acid was utilized as an oxidizer.     

Proton transport properties in an ionic liquid having a hydroxyl group

An ionic liquid having a hydroxyl group, choline bis(trifluoromethylsulfonyl)amide ([N(111(2OH))][N(Tf)(2)]), was synthesized to investigate the effect of hydroxyl groups on the proton transport. 1,1,1-Trifluoro-N-(trifluoromethylsulfonyl)methanesulfoneamide (HN(Tf)(2)) as a proton source was mixed with the choline derivative at various molar ratios. Their thermal properties, viscosities, and ionic conductivities were investigated. [N(111(2OH))][N(Tf)(2)] showed a melting point at 27 °C, and its thermal stability was higher than 400 °C. The viscosity of [N(111(2OH))][N(Tf)(2)]/HN(Tf)(2) mixtures increased as the acid molar fraction increased. The ionic conductivity of [N(111(2OH))][N(Tf)(2)] was 2.1 × 10(-3) S cm(-1) at 25 °C; the ionic conductivity monotonously decreased as the acid molar fraction increased. There was a clear correlation between the ionic conductivity and the viscosity for the mixtures of the choline derivative and the acid. PFG-NMR measurements were carried out to investigate the diffusion behavior of protons. Although the acid and the hydroxyl group were indistinguishable by (1)H NMR, the self-diffusion coefficient of the (1)H of the hydroxyl group and the acid was larger than those of other (1)H nuclei. This difference suggests that a fast intermolecular proton transfer exists between the hydroxyl group and the acid.     

Alkylation of alkali metal salts of hydroperoxides with haloalkanes in dipolar nonhydroxyl solvents

The possibility of alkylation with chloroalkanes of cumyl hydroperoxide sodium salt hexahydrate in dopolar nonhydroxyl solvents with high donor numbers was examined. The kinetic featutes of the process in hexamethylphosphoric triamide were studied.     

A kinematic approach to ionic transport in aqueous electrolyte solutions and structural theory of hydration of alkali metal ions

While considering the self-diffusion processes in aqueous electrolyte solutions, transport of ions, not only by jumps of single ions, but also by jumps of their solvation shells, are to be taken into account. Samoilov estimated the relative number of the two kinds of ionic jumps from experimental data on diffusion assuming an approximately uniform value for the α factor. In the present paper entirely different theory of the α factor based on the structural hydration model of one of the authors (S.V.T.) for alkali metal ions is given and its ion-wise values are calculated at different temperatures. The theory not only dispenses with the approximate fixation of α but also throws light on the structure of water, formation of clusters and their population variation with temperature.     

Thermotropic liquid crystals from alkali metal dihexadecylphosphates

Lithium, sodium, potassium, rubidium, and caesium dihexadecylphosphates were synthesized. Their thermal stability was checked by thermogravimetry. Their ability to show thermotropic mesomorphic behaviour was investigated using differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. All these compounds were found to exhibit a lamellar structure in the crystalline state at room temperature and a columnar structure of hexagonal symmetry in the mesomorphic state at high temperature. The potassium, rubidium, and caesium derivatives were found to exhibit an additional Ia 3 d body-centred cubic structure in the temperature range between the crystal and the columnar phase. Structures and structural parameters are briefly discussed.     

Ion transport in polymerized lyotropic liquid crystals containing ionic liquid

In this work, we investigate the effect of morphology and segmental dynamics on ion transport in polymerized lyotropic liquid crystals (polyLLCs) containing 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). We demonstrate that two important factors, which affect ion conduction in polyLLCs, are grain size and chain density at the interface. The polyLLC with large grain size (70 nm) shows significant reduction in ion conductivity (one order of magnitude) compared to its homopolymer/IL mixture. However, the polyLLC with small grain size (20 nm) has little difference in ion conductivity compared to its homopolymer/IL mixture. It is observed that decreasing the chain density enhances the interaction of IL with polymer chains and consequently slows the relaxation of polymer chains. In addition, comparing the dynamics of polymer chains in mixtures of homopolymer/IL and templated LLC mesophases shows that the confinement in LLC structure prolongs the relaxation of polymer chains.     

Photo-induced carrier mediated transport of alkali metal salts

A new, long-alkyl-group spiropyran compound, 1-octadecyl-3,3-dimethyl-6′-nitrospiro(indoline-2,2′-2H-benzopyran), was synthesized which showed photochromism similar to spiropyran compounds reported previously. Its ability as a salt transporting carrier was investigated by using it in a 1-octanol liquid membrane. The salt NaCl was concentrated from the dark to the visible light illuminated side across the anisotropic membrane using the conditions whereby one interface between liquid membrane and aqueous phase was illuminated with visible light and the remaining was kept dark. In the KClNaCl binary system, more NaCl was transported than KCl.     

Charge transport mediated by d-orbitals in transition metal complexes

This communication reports an asymmetric charge transport with a large rectification ratio and finely featured NDR (negative differential resistance) by d-orbitals of a neutral ruthenium(ii) complex with a C(2) axis of symmetry.     

Task-specific ionic liquid for solubilizing metal oxides

Protonated betaine bis(trifluoromethylsulfonyl)imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese(II) oxide, and silver(I) oxide. Insoluble or very poorly soluble are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After transfer of the metal ions to the aqueous phase, the ionic liquid can be recycled for reuse. Betainium bis(trifluoromethylsulfonyl)imide forms one phase with water at high temperatures, whereas phase separation occurs below 55.5 degrees C (temperature switch behavior). The mixtures of the ionic liquid with water also show a pH-dependent phase behavior: two phases occur at low pH, whereas one phase is present under neutral or alkaline conditions. The structures, the energetics, and the charge distribution of the betaine cation and the bis(trifluoromethylsulfonyl)imide anion, as well as the cation-anion pairs, were studied by density functional theory calculations.     

Sub-Tg relaxations due to dipolar solutes in nonpolar glass-forming solvents

It is well known that rigid dipolar solutes (in smaller quantity) dispersed in a nonpolar glassy matrix exhibit a sub-T(g) (or beta(s)) relaxation due to the solute often designated as Johari-Goldstein (JG) relaxation, which is intermolecular in nature. In this article, we report the results of our study of such a sub-T(g) process in a wide variety of dipolar solutes in different glassy systems using dielectric spectroscopy over a frequency range of 20-10(6) Hz down to a temperature of 77 K. The T(g) of these solutions are determined using differential scanning calorimetry. The solvents used in this study are o-terphenyl (OTP), isopropylbenzene (IPB), and methylcyclohexane. In the case of rigid molecular solutes, like mono-halogen benzenes, the activation energy (DeltaE(beta)) of the beta(s) process is found to increase with decreasing T(g) of the solvent, with a corresponding decrease in the magnitude of the beta(s) process. In the case of more symmetrical molecular solute, for example, tert-butylchloride, the change in DeltaE(beta) is not very appreciable. These results emphasize the importance of the size of the cage of the host matrix in the relaxation of the solute molecules. We have also studied the sub-T(g) relaxation(s) due to some flexible molecular solutes, viz., 1butylbromide, 1hexylbromide, 1butylacetate, and benzylacetate. These solutes in IPB matrix exhibit only one relaxation, whereas in OTP matrix they exhibit an additional sub-T(g) process, which may be identified with a JG type of relaxation. These observations lead us to the conclusion that the beta process observed in the glassy states of these pure solutes is predominantly intramolecular in nature.     

Collective excitations in an ionic liquid

Collective dynamics in a representative model of ionic liquids, namely, 1-butyl-3-methylimidazolium chloride, have been revealed by molecular dynamics simulation. Dispersion of energy excitation, omega versus k, of longitudinal acoustic (LA) and transverse acoustic (TA) modes was obtained in the wave vector range 0.17 < k < 1.40 Angstroms(-1), which encompasses the main peak of the static structure factor S(k). Linear dispersion of acoustic modes is observed up to k approximately 0.7 Angstroms(-1). Due to mixing between LA and TA modes, LA spectra display transverselike component, and vice versa. Due to anisotropy in short-time ionic dynamics, acoustic modes achieve distinct limiting omega values at high k when the cation displacement is projected either along the plane or perpendicular to the plane of the imidazolium ring. In charge current spectra, branch with negative dispersion of omega versus k is a signature of optic modes in the simulated ionic liquid. Conductivity kappa estimated by using ionic diffusion coefficients in the Nernst-Einstein equation is higher than the actual kappa calculated by integrating the charge current correlation function. From TA spectra, a wave vector dependent viscosity eta(k) has been evaluated, whose low-k limit gives eta in reasonable agreement with experimental data.     

Equilibrium potentials and charge transport of an I-/I3- redox couple in an ionic liquid

Equilibrium potentials and charge transport of an I-/I3- redox couple in an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, are revealed by using a microelectrode technique, where the anomaly of the charge transport at high concentrations of the redox couple with comparable [I-] and [I3-] can be attributed to the exchange reaction of I- + I3- --> I3- + I-.     

Intermolecular vibrations and fast relaxations in supercooled ionic liquids

Short-time dynamics of ionic liquids has been investigated by low-frequency Raman spectroscopy (4 < ω < 100 cm(-1)) within the supercooled liquid range. Raman spectra are reported for ionic liquids with the same anion, bis(trifluoromethylsulfonyl)imide, and different cations: 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-butyl-1-methylpiperidinium, trimethylbutylammonium, and tributylmethylammonium. It is shown that low-frequency Raman spectroscopy provides similar results as optical Kerr effect (OKE) spectroscopy, which has been used to study intermolecular vibrations in ionic liquids. The comparison of ionic liquids containing aromatic and non-aromatic cations identifies the characteristic feature in Raman spectra usually assigned to librational motion of the imidazolium ring. The strength of the fast relaxations (quasi-elastic scattering, QES) and the intermolecular vibrational contribution (boson peak) of ionic liquids with non-aromatic cations are significantly lower than imidazolium ionic liquids. A correlation length assigned to the boson peak vibrations was estimated from the frequency of the maximum of the boson peak and experimental data of sound velocity. The correlation length related to the boson peak (～19 A?) does not change with the length of the alkyl chain in imidazolium cations, in contrast to the position of the first-sharp diffraction peak observed in neutron and X-ray scattering measurements of ionic liquids. The rate of change of the QES intensity in the supercooled liquid range is compared with data of excess entropy, free volume, and mean-squared displacement recently reported for ionic liquids. The temperature dependence of the QES intensity in ionic liquids illustrates relationships between short-time dynamics and long-time structural relaxation that have been proposed for glass-forming liquids.     

Nanocomposite ion gels based on silica nanoparticles and an ionic liquid: ionic transport, viscoelastic properties, and microstructure

The dispersion of silica nanoparticles made an ionic liquid, 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide ([C(2)mim][NTf(2)]), gelled even by the addition of 2-3 wt %, due to the formation of interconnected particulate silica networks in [C(2)mim][NTf(2)]. The ionic transport and viscoelastic properties of these nanocomposite ion gels were investigated in relation to the microstructure. Despite their solid-like behavior, the nanocomposite ion gels exhibited a high ionic conductivity of approximately 10(-2) S cm(-1) at 30 degrees C, which is comparable to that of neat [C(2)mim][NTf(2)]. Intriguing viscoelastic responses, such as shear-thinning and shear-induced sol-gel transitions, were found in all of the nanocomposite ion gels. By adjusting the silica concentration, the elastic modulus ( G') could be precisely controlled in a range of more than 3 orders of magnitude and reached approximately 10(6) Pa without a considerable decrease in the ionic conductivity; the characteristic viscoelastic response was also maintained. For the aggregation mechanism in [C 2 mim][NTf(2)], the reaction-limited cluster aggregation (RLCA) model was proposed by rheology and light scattering measurements.     

Lyotropic liquid crystalline phases formed in an ionic liquid

Lyotropic liquid crystalline phases of an amphiphilic block copolymer are constructed and characterized in an ionic liquid with comparison of component and temperature effects.     

Aggregation behavior of long-chain ionic liquids in an ionic liquid

The aggregation behavior of long-chain ionic liquids 1-alkyl-3-methylimidazolium bromide (C(n)mimBr) in another ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), was studied for the first time. Surface tension measurements revealed that aggregates are formed by C(n)mimBr, and freeze fracture transmission electron microscopy (FF-TEM) observations suggested the aggregates are spheres with a size much larger than traditional micelles. The sizes of the aggregates were further confirmed by dynamic light scattering (DLS) measurements.     

Hard-wall potential function for transport properties of alkali metal vapors

This study demonstrates that the transport properties of alkali metals are determined principally by the repulsive wall of the pair interaction potential function. The (hard-wall) Lennard-Jones (LJ) (15-6) effective pair potential function is used to calculate the transport collision integrals. Accordingly, reduced collision integrals of K, Rb, and Cs metal vapors are obtained from the Chapman-Enskog solution of the Boltzmann equation. The law of corresponding states based on the experimental transport reduced collision integral is used to verify the validity of a LJ(15-6) hybrid potential in describing the transport properties. LJ(8.5-4) potential function and a simple thermodynamic argument with the input PVT data of liquid metals provide the required molecular potential parameters. Values of the predicted viscosity of monatomic alkali metal vapor are in agreement with typical experimental data with average absolute deviations of 2.97% for K in the range of 700-1500 K, 1.69% for Rb, and 1.75% for Cs in the range of 700-2000 K. In the same way, the values of predicted thermal conductivity are in agreement with experiment within 2.78%, 3.25%, and 3.63% for K, Rb, and Cs, respectively. The LJ(15-6) hybrid potential with a hard-wall repulsion character conclusively predicts the best transport properties of the three alkali metal vapors.     

Reconstructions and relaxations on metal surfaces

On metal surfaces the top layer of atoms usually relaxes inwards, and several metal surfaces reconstruct, particularly W and Mo (001) and Ir, Pt and Au (001) and (110). This paper reviews the electronic origins of these atomic displacements, and the physical effects which they lead to. The surface relaxations are explained in terms of the change in balance between electronic forces at the surface. The W (001) surface reconstructs from (1 × 1) to (?2 × ?2)R45° in a continuous phase transition on cooling below room temperature, and the structure of these phases and the nature of the phase transition are discussed. The driving force for the reconstruction is discussed in terms of calculations and photoemission studies of the surface electronic structure. Phenomenological Landau theory is used to describe the effect of surface steps on the transition, and the origin of the long wavelength modulation in the Mo (001) reconstruction. Finally the reconstructions of Ir, Pt and Au (001) and (110) are briefly described; these involve a more substantial movement of atoms than in the W and Mo reconstructions.