Dynamics of the interfacial film in bicontinuous microemulsions based on a partly ionic surfactant mixture: A neutron spin-echo study

In a microemulsion system based on a mixture of nonionic and ionic surfactants the addition of alcohol instead of changing the temperature was used to tune the curvature of the surfactant interface. The influence of the addition of the short-chain alcohol 2-propanol in the system water-perchloroethylene-Marlowet IHF-2-propanol is studied using neutron spin-echo spectroscopy. In contrast to alcohols with long alkyl chains 2-propanol is no strong co-surfactant, but changes the properties of the solvents. The present contribution focuses on the bicontinuous phase in this system and a quantitative analysis of the obtained neutron spin-echo data is proposed within the theoretical framework given by Zilman and Granek for amphiphilic membranes. It turns out that, in addition to the local movements of the surfactant film, also a collective diffusional mode of the bicontinuous structure has to be taken into account. The presented approach allows to calculate the bending elastic constant k \kappa of the film. The approach is subsequently applied to follow changes of k \kappa as induced by changes of the alcohol concentration.     

A prospective DFT study for assembling highly reactive clusters based on lithium boranes and alanates

In this work, first-principles calculations using the density functional theory are performed to study the structure, stability and electronic properties of lithium borohydrides (boranes) and lithium aluminohydrides (alanates). With the attachment of BH₄ and AlH₄ complexes to the Li atom, the electron affinity increases to 5.22 eV and 4.34 eV, in the clusters Li(BH₄)₂ and Li(AlH₄)₂, respectively, which indicate superhalogen behaviour. For the alanates, by decorating the Li atom with the superhalogen moiety, the electron affinity increases to 4.64 eV, in the large-sized cluster Li[Li(AlH₄)₂]₂. The substitution of Al for B leads to larger NBO charges on the H atoms, as a result of the electron- donating character of the Al atom. The results show that, besides larger gravimetrical storage capacities, the boranes also have higher electron affinities than the alanates in the large-sized clusters. The significant HOMO-LUMO differences indicate that the new moieties, which are highly reactive, are chemically very stable species.     

A FT-IR spectroscopic study of ultrasound effect on aqueous imidazole based ionic liquids having different counter ions

Ultrasound (US) effect on 1-butyl-3-methyl-imidazolium (BMI) ionic liquids having different counter anions, BF₄⁻, PF₆⁻ and Cl⁻ in aqueous medium was studied by FT-IR spectroscopy. Their deconvolution spectra were used to analyze the change of hydrogen bond in the absence and presence of US exposure to the ionic liquid. The FT-IR spectra were measured in different water contents without and with US at 23 kHz. These results indicated that the counter anion species in the imidazole based the ionic liquids played an important role for water solvation, when the US was exposed. The US hardly changed hydrogen bonding in the aqueous BMI–PF₆, while the BMI–BF₄ and BMI–Cl showed obvious change in their FT-IR spectra. Especially for the BMI–Cl, significant change was observed by the US exposure in the range of 2.6 wt% to 20 wt% of water contents. The results showed that the US could break the hydrogen bond in the BMI–Cl ionic liquids. In the case of BMI–BF₄, the FT-IR band at 950–1152 cm⁻¹ was significantly intensified under US exposure, due to that the US influenced BF₄⁻-water interaction. But, it was observed that the ionic liquid having PF₆⁻ was very less changed in the US system.     

Energetic Particle Physics on the HL-2A Tokamak: A Review

Interaction between shear Alfvén wave(SAW) and energetic particles(EPs) is one of major concerns in magnetically confined plasmas since it may lead to excitation of toroidal symmetry breaking collective instabilities,thus enhances loss of EPs and degrades plasma confinement. In the last few years, Alfvénic zoology has been constructed on HL-2A tokamak and series of EPs driven instabilities, such as toroidal Alfvén eigenmodes(TAEs),revered shear Alfvén eigenmodes(RSAEs), beta induced Alfvén eigenmodes(BAEs), Alfvénic ion temperature gradient(AITG) modes and fishbone modes, have been observed and investigated. Those Alfvénic fluctuations show frequency chirping behaviors through nonlinear wave-particle route, and contribute to generation of axisymmetric modes by nonlinear wave-wave resonance in the presence of strong tearing modes. It is proved that the plasma confinement is affected by Alfvénic activities from multiple aspects. The RSAEs resonate with thermal ions, and this results in an energy diffusive transport process while the nonlinear mode coupling between core-localized TAEs and tearing modes trigger avalanche electron heat transport events. Effective measures have been taken to control SAW fluctuations and the fishbone activities are suppressed by electron cyclotron resonance heating. Those experimental results will not only contribute to better understandings of energetic particles physics, but also provide technology bases for active control of Alfvénic modes on International Thermonuclear Experimental Reactor(ITER) and Chinese Fusion Engineering Testing Reactor(CFETR).     

Energetic and structural evolution of gold nanowire under heating process: A molecular dynamics study

The energetic and structural evolution of a squared gold nanowire under heating process is investigated via molecular dynamics with many-body potential. The simulations reveal that the nanowire undergoes distinct energetic and structural developments during the following four heating processes: low temperature, melting, breaking and high temperature. The cross-section of nanowire is found to change from a square to a circle shape with rising temperature at first. A neck is then found to be initiated above the overall melting point, followed by the formation of a two- to five-atom-thick chain structure before the breaking of neck. The nanowire transforms to a spherical cluster after the final breaking.     

A theoretical study on calculation of ionic radii using limiting equivalent conductivities

Graphs of the total radius (the distance between an anionic nuclei and a cationic nuclei in a crystal) of sodium halides and alkali metal fluorides versus total limiting equivalent conductivities were plotted. For the hard ions Na⁺ and F⁻, whose behaviour approaches a hard spherical model, it was determined that radii values could be obtained using differences in limiting equivalent conductivities and ionic crystal data. From the determined radii of sodium and fluoride ions and known crystal data, radii of other alkali metal halides were calculated.

A quantum-chemical study on ion complexation in polymer electrolytes containing lithium aluminate salts

A quantum-chemical study on single-ion conducting electrolytes based on lithium aluminate salts is presented. Geometry optimizations for salts and corresponding anions have been performed. Stabilization energies for Li⁺ complexed at aluminate anions have been calculated. Information about Li⁺ coordination changes has been obtained from Born–Oppenheimer Molecular Dynamics simulations. Complexation energies for lithium cation have been shown to correlate with experimental conductivity values [T. Fujinami, Y. Buzoujima, J. Power Sources 119–121 (2003) 438].     

A computer simulation study of ionic conductivity in polymer electrolytes

In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganization of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH₄I and PEO-NH₄SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.     

A study of frequency and temperature dependence of ionic conductance

An approach to study the frequency and temperature dependence of the bulk ionic conductivity, based on the log-log representation of the frequency response, is described. Experimental results obtained on -PbF₂ thin-film samples are used to illustrate this approach. The analysis of these results permits to separate the different physical mechanisms involved and to model the cells. Using CPE (Constant Phase Element) Y=Y ₀(j) ⁿ for the interfaces, but also for the bulk ionic conductance, permits to fit the experimental results. A progressive increase of the slope n of the admittance which corresponds to the bulk ionic conductivity is observed when the temperature decreases. A graphical method is described which can be used to determine the activation energy in this case of a CPE behavior of the conductance. It is based on the obtention of a unique curye which describes the frequency and temperature dependence of the reduced conductance G=Y _r T plotted versus the reduced radial frequency u=. This curve shows the whole conductance variation which starts from pure transport with n=0 at low frequencies and high temperature, and tends for high frequencies or low temperatures toward the dielectric response (n1), corresponding to ion displacements limited to only one jump. The observed CPE behavior of the conductance at constant temperature thus appears to be the result of the very slow variation rate of the slope n of the reduced conductance versus the radial frequency.     

Electrolyte based on fluorinated cyclic quaternary ammonium ionic liquids

Ionic liquids, ILs, based on fluorinated pyrrolidinium and piperidinium ammonium cations and imide anion were prepared and characterized. The physicochemical and electrochemical properties of these ILs including melting point, glass transition and degradation temperatures, viscosity, ionic conductivity, and electrochemical stability were determined and compared to alkyl pyrrolidinium and piperidinium ILs. The incorporation of a CF₃ group instead of a CH₃ induces an increase of the IL viscosity, thus a conductivity decrease. However, good ionic conductivity is obtained with fluorinated pyrrolidinium IL. Cyclic amine ILs with propyl alkyl chain or fluorinated ammonium exhibit very high electrochemical stability toward oxidation. The effect of the addition of LiTFSI on the IL properties was studied with the same methodology.     

A Raman study of lithium fluoride containing fast ionic conducting glasses

The role of fluorine in the structure of fluoro-borate fast ionic conducting glasses has been studied by Raman spectroscopy. It is shown that addition of LiF results in important structural changes, compared to binary glasses with the same O/B ratio. The Raman results are consistent with the participation of fluorine in the network. Careful control of the O/B ratio is required in order to detect the alkali fluoride-induced structural changes by Raman spectroscopy.     

A Li K‐edge XANES study of salts and minerals

The first comprehensive Li K‐edge XANES study of a varied suite of Li‐bearing minerals is presented. Drastic changes in the bonding environment for lithium are demonstrated and this can be monitored using the position and intensity of the main Li K‐absorption edge. The complex silicates confirm the assignment of the absorption edge to be a convolution of triply degenerate p‐like states as previously proposed for simple lithium compounds. The Li K‐edge position depends on the electronegativity of the element to which it is bound. The intensity of the first peak varies depending on the existence of a 2p electron and can be used to evaluate the degree of ionicity of the bond. The presence of a 2p electron results in a weak first‐peak intensity. The maximum intensity of the absorption edge shifts to lower energy with increasing SiO₂ content for the lithium aluminosilicate minerals. The bond length distortion of the lithium aluminosilicates decreases with increasing SiO₂ content, thus increased distortion leads to an increase in edge energy which measures lithium's electron affinity.     

Ab-initio study of fluorine-doped tin dioxide: A prospective catalyst support for water electrolysis

In an attempt to identify new electrochemically stable catalyst supports for electrolysis of water, the electronic structure of SnO₂ doped with different fluorine concentrations has been calculated using the Vienna ab-initio simulation package (VASP) in the projector-augmented wave (PAW) method with the general gradient approximation (GGA) for conducting the exchange-correlation corrections. The role of fluorine in improving the electronic conductivity is discussed. An increase in the density of electronic states at the Fermi level with increase in the concentration of fluorine incorporated into the main SnO₂ matrix agrees well with published experimental observations. Despite a gradual decrease in the cohesive energies for the fluorine-doped tin oxide with increase in fluorine concentration, the doped material still remains an appropriate candidate for use as catalyst supports in water electrolysis warranting further experimental validation.     

基于熵的离子导体电导率公式推导

电导率是表示导体导电能力强弱的度量,离子导体的电导率可以通过平均漂移速度求得.文中通过对离子导体的分析,给出一种基于熵的新的推导方法.首先分析系统熵和环境熵的竞争关系,其次运用熵最大原理求出最概然电流,进而导出电导率公式.最后将基于熵的推导方法与漂移速度方法加以区别和对比,并推广到一般导体电导率公式的推导.     

Nanocomposites based on exfoliated NbWO6 nanosheets and ionic polyacetylenes

Nanocomposites based on exfoliated NbWO₆ nanosheets and poly (N-methyl-2-ethynyl pyridinium iodide) (PNMe) or poly (N-octadecyl-2-ethynyl pyridinium bromide) (PNO) have been synthesized by exfoliation–reflocculation method. The XRD data of the NbWO₆:PNMe nanocomposite indicates the formation of NbWO₆/PNMe nanostructure with an interlayer expansion of 2.16 nm along the stacking direction of NbWO₆ nanosheets. Whereas, the XRD data of the PNO:NbWO₆ nanocomposite indicates the formation of NbWO₆/PNO nanostructure with an interlayer expansion of 4.6 nm along the stacking direction of NbWO₆ nanosheets. Formation of these nanocomposites is further supported by the results obtained by FT-IR spectroscopy, transmission electron microscopy and thermogravimetry. The values of electrical conductivity of the polymers and nanocomposites were also measured.     

Ferroelectric phase transitions in ionic conductors based on bismuth vadanate

Ceramic solid solutions (Bi_{1 ? x} La _x )₄V₂O_{11 ? z} (I), Bi₄(V_{1 ? x} Fe _x )₂O_{11 ? y} (II), and (Bi_{1 ? x} La _x )₄(V_0.96Fe_0.04)₂O_{11 ? y} (III) (x = 0–0.3, step Δx = 0.02) are prepared using solid-phase synthesis. The concentration and temperature ranges of stabilization of different polymorphic modifications, including the ranges of concentrations x corresponding to the stabilization of the ferroelectric phase, are established. It is revealed that an increase in the concentration x in the region of existence of the pseudoorthorhombic phase α of the solid solutions studied leads to a decrease in the transition temperature, smearing of the transition, and an increase in the width of the thermal hysteresis of the ferroelectric phase transition. The effect of compressing of the domain walls by oxygen vacancies was revealed in the samples from the region of existence of the ferroelectric α phase, and the effect of dielectric relaxation was detected in the samples from the region of existence of the orthorhombic phase β.     

Solid polymer electrolytes based on poly(lithium carboxylate) salts

The ionic conductivity, lithium ion transference number, electrochemical stability, and thermal property of solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and poly(lithium carboxylate)s, (poly(lithium acrylate) (Poly(Li-A)) or poly(lithium fumarate) (Poly(Li-F)), with and without BF₃·OEt₂ were investigated. The ionic conductivities of all solid polymer electrolytes were enhanced by one to two orders of magnitude with addition of BF₃·OEt₂ because the dissociation of lithium ion and carboxylate anion was promoted by the complexation with BF₃. The lithium ion transference number in the solid polymer electrolytes based on poly(lithium carboxylate)s showed relatively high values of 0.41–0.70, due to the suppression of the transport of counter anion by the use of a polymeric anion. The solid polymer electrolytes with addition of BF₃·OEt₂ showed good electrochemical stability.     

A study of ionic solids by means of new density-functional theory techniques

Summary The lattice parameter, the bulk modulus and the dissociation energy of NaCl and MgO are calculated by a method which allows the direct determination of the total energy and of the charge density of a crystal. An extensive comparison with the results of standard band structure calculations is reported. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

A comparative study of optic phonon-like excitations in liquid mixtures and molten salts

We report a study of collective excitations in an equimolar Lennard–Jones liquid mixture KrAr and a molten salt NaCl within the parameter-free generalized collective modes (GCM) approach. It is shown that the high-frequency propagating modes in liquid KrAr and molten NaCl correspond to optic phonon-like excitations, caused by fast mass-concentration (charge in NaCl) fluctuations. Dispersion curves for optic collective excitations are discussed.