From colloidal stability in ionic liquids to advanced soft materials using unique media

Owing to their fascinating properties, ionic liquids (ILs) are now receiving a great deal of attention as alternatives to organic solvents and electrolyte solutions and as synthetic and dispersion media for colloidal systems. Colloidal stability is an essential factor in determining the properties and performance of colloidal systems combined with ILs. The remarkable properties of ILs primarily originate from their highly ionic nature. Although such high ionic strength often causes colloidal aggregation in aqueous and organic suspensions, some colloidal particles can be well suspended in ILs without any stabilizers. In the first part of this article, we focus on recent experiments conducted to investigate the colloidal stability of bare and polymer-grafted silica nanoparticles and on the surface force between silica substrates and ILs. Three different repulsions between colloidal particles (i.e., electrostatic, steric, and solvation forces) are also highlighted, after which a possible interpretation of the results in terms of the stabilization mechanism in ILs both in the presence and in the absence of stabilizers is proposed. The latter part of this article provides an overview of our recent studies on colloidal soft materials with ILs. On the basis of the dispersed states of the silica colloids in ILs, two different soft materials, a colloidal gel and a colloidal glass in ILs, were fabricated. The relationship between their functional properties, such as ionic transport, rheological properties, and optical properties, and the microstructure of the colloidal materials is also described.     

Feasibility study of the standing accretion shock instability experiment at the National Ignition Facility

The primary hydrodynamic flow feature of early explosion phases of a core-collapse supernova is a spherical shock. This shock is born deep in the central regions of the collapsing stellar core, stalls shortly afterward, and in case of a successful explosion is revived and becomes the supernova shock. The revival process involves a standing accretion shock instability, SASI. This shock instability is considered the key processes aiding the core-collapse supernova (ccSN) explosion.The aim of our study is to identify feasible conditions and parameters for an experimental system that is able to capture the essential characteristics of SASI. We use semi-analytic methods and high-resolution hydrodynamic simulations in multidimensions to investigate a possible experimental design on the National Ignition Facility. The experimental configuration involves a steady, spherical shock. We explore a viable region of parameters and obtain limits on the shocked flow geometry. We study the stability properties of the shock and its post-shock region.We compare properties of the experimental design and the ccSN environment. The obtained model experimental flow field closely resembles converging nozzle flow. The post-shock region, in contrast to the supernova setting, is found to be stably stratified and stable against to perturbations upstream of the shock. We conclude that it is not possible to capture the characteristics of the ccSN SASI for the converging shocked flow configuration considered here. However, such configuration offers a very stable setting for precision studies of dense, high-temperature plasmas requiring finely-controlled conditions and long lifetimes.     

Shockwaves and filaments induced by counter-streaming laser-produced plasmas

The interaction between two counter-streaming laser-produced plasmas is studied with shadowgraph and interferometry on the Shenguang II (SG-II) laser facility. Shockwaves and filaments are observed at different timing. The simulation and theoretical analysis indicate that these structures are probably induced by collisionless mechanisms.     

Electrochemical Formation of Fe(IV)=O Derived from H2O2 on a Hematite Electrode as an Active Catalytic Site for Selective Hydrocarbon Oxidation Reactions

The high-valence iron species (Fe(IV)=O) in the cytochrome P450 enzyme superfamily is generated via the activation of O₂, and serves as the active center of selective hydrocarbon oxidation reactions. Furthermore, P450 can employ an alternate route to produce Fe(IV)=O, even from H₂O₂ without O₂ activation. Meanwhile, Fe(IV)=O has recently been revealed to be the reactive intermediate during H₂O oxidation to O₂ on hematite electrodes. Herein, we demonstrated the generation of Fe(IV)=O on hematite electrodes during the electrochemical oxidative decomposition of H₂O₂ using in situ UV-visible absorption spectra. The generation of Fe(IV)=O on hematite electrodes from H₂O₂ exhibited 100 mV lower overpotential than that from H₂O. This is because H₂O₂ serves not only as the oxygen source of Fe(IV)=O, but also as the additional oxidant. Finally, we confirmed that the Fe(IV)=O generated on hematite electrodes can serve as the catalytic site for styrene epoxidation reactions.     

Ablative Rayleigh-Taylor instability at short wavelengths observed with moiré interferometry

One of the most important quantities to be measured for better understanding of the ablative Rayleigh-Taylor (RT) instability is the growth rate in the short wavelength region at which the RT instability is significantly reduced. The short wavelength ( 4.7-12 microm) RT growth rates for direct-drive targets were measured for the first time by utilizing the innovated moiré interferometry [M. Matsuoka et al., Rev. Sci. Instrum. 70, 637 (1999)]. These growth rates were reasonably well reproduced by the simulation that solves the Fokker-Planck equation for nonlocal heat transport.     

X ray crystallography of (+)-(R)p methyl phenyl phosphoramidate of ethyl L-phenylalaninate

The absolute configuration of (+)-(R)_p methyl phenyl phosphoramidate of ethyl L-phenylalaninate $\text{1}$ was determined by X ray crystallography.     

Ammonium tungstate modified Li-rich Li<Subscript>1+x</Subscript>Ni<Subscript>0.35</Subscript>Co<Subscript>0.35</Subscript>Mn<Subscript>0.30</Subscript>O<Subscript>2</Subscript> to improve rate capability and productivity of lithium-ion batteries

LiNi_1-x-yCo_xMn_yO₂ (NCM) with excessive lithium is known to exhibit high rate capability and charge–discharge cycling durability. However, the practical usage of NCM is difficult, because the positive electrode slurry is unstable and battery cells swell due to the alkaline residual lithium compound generated on the surface of NCM particles. To reduce the residual lithium compound, ammonium metatungstate (AMT) added to NCM is studied, and the effect is investigated by scanning electron microscopy, aberration-corrected scanning transmission electron microscopy, X-ray diffractometry, synchrotron X-ray diffractometry, and several electrochemical measurements. It is found that the AMT modification reduces the amount of alkaline residual lithium compound and improves the rate capability due to the ~1-nm-thick W-rich layer generated on the NCM surface.

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Electronic stress tensor analysis of molecules in gas phase of CVD process for gesbte alloy

We analyze the electronic structure of molecules which may exist in gas phase of chemical vapor deposition process for GeSbTe alloy using the electronic stress tensor, with special focus on the chemical bonds between Ge, Sb, and Te atoms. We find that, from the viewpoint of the electronic stress tensor, they have intermediate properties between alkali metals and hydrocarbon molecules. We also study the correlation between the bond order which is defined based on the electronic stress tensor, and energy‐related quantities. We find that the correlation with the bond dissociation energy is not so strong while one with the force constant is very strong. We interpret these results in terms of the energy density on the “Lagrange surface,” which is considered to define the boundary surface of atoms in a molecule in the framework of the electronic stress tensor analysis. © 2015 Wiley Periodicals, Inc.     

Copper‐Modified Covalent Triazine Frameworks as Non‐Noble‐Metal Electrocatalysts for Oxygen Reduction

The electrochemical oxygen reduction reaction (ORR) is an important cathode reaction of various types of fuel cells. The development of electrocatalysts composed only of abundant elements is a key goal because currently only platinum is a suitable catalyst for ORR. Herein, we synthesized copper‐modified covalent triazine frameworks (CTF) hybridized with carbon nanoparticles (Cu‐CTF/CPs) as efficient electrocatalysts for the ORR in neutral solutions. The ORR onset potential of the synthesized Cu‐CTF/CP was 810 mV versus the reversible hydrogen electrode (RHE; pH 7), the highest reported value at neutral pH for synthetic Cu‐based electrocatalysts. Cu‐CTF/CP also displayed higher stability than a Cu‐based molecular complex at neutral pH during the ORR, a property that was likely as a result of the covalently cross‐linked structure of CTF. This work may provide a new platform for the synthesis of durable non‐noble‐metal electrocatalysts for various target reactions.