Oxidation products of the niobium tungsten oxide Nb4W13O47: A high-resolution scanning transmission electron microscopy study

Nb₄W₁₃O₄₇, a member of the solid solution series Nb_8−nW_9+nO₄₇ (0?n?5), crystallizes in a threefold superstructure of the tetragonal tungsten bronze structure. While the oxidation of this reduced phase at T_OX=1200 °C leads to a separation into the thermodynamically stable phases, lower oxidation temperatures result in products that comprise new structural elements and ordering variants. The characterization of the oxidation products obtained at T_OX=1000 °C was performed by scanning transmission electron microscopy applying a high-angle annular dark field detector. At the selected imaging conditions (Z contrast), not only the metal positions are revealed by this technique but valuable additional information about the elemental distribution can be obtained simultaneously.     

On the equation of state of classical one-component systems with long-range forces

Several definitions of the pressure are introduced for one-component systems and shown to be nonequivalent in the presence of a rigid neutralizing background. Relations between these pressures are derived for finite and infinite systems; these relations depend on the asymptotic behavior of the force at infinity, with the Coulomb force at the borderline between different properties. It is argued that only one of those definitions is physically acceptable and its properties are discussed in relation to the asymptotic behavior of the force. It is seen in particular that a knowledge of the state of the infinite system is not sufficient to determine its thermodynamic properties. The results are illustrated by some typical examples.For example, for two-dimensional systems with three-dimensional Coulomb interaction see refs. 2–4.     

纳米分辨率的三维形貌检测仪

从光干涉方式，瞳窗关系和光源带宽等基本关系出发，利用空间不变系统理论解析了相移显微干涉检测系统中衍射效应的影响。为了减小横向分辨率对纵向分辨率的影响，利用相关信息提取或数字滤波的方法，获得了纳米分辨率的三维形貌。     

Interactions between Adsorbed Layers of a Low Charge Density Cationic Polyelectrolyte on Mica in the Absence and Presence of Anionic Surfactant

Interactions between two negatively charged mica surfaces across aqueous solutions containing various amounts of a 10% charged cationic polyelectrolyte have been studied. It is found that the mica surface charge is neutralized when the polyelectrolyte is adsorbed from a 10–50 ppm aqueous solution. Consequently no electrostatic double-layer force is observed. Instead an attractive force acts between the surfaces in the distance regime 250–100 Å. We suggest that this attraction is caused by bridging. Additional adsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion develops. This repulsive force is both of electrostatic and steric origin. The polyelectrolyte layer adsorbed from a 50 ppm solution does not desorb when the polyelectrolyte solution is replaced with an aqueous polyelectrolyte-free solution. Injection of sodium dodecyl sulfate (SDS) into the measuring chamber to a concentration of about 0.01 CMC (8.3 × 10⁻⁵M) does not affect the adsorbed layers or the interaction forces. However, when the SDS concentration is increased to 0.02 CMC (0.166 mM) the adsorbed layer expands dramatically due to adsorption of SDS to the polyelectrolyte chains. The sudden swelling suggests a cooperative adsorption of SDS to the preadsorbed polyelectrolyte layer and that the critical aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the polyelectrolyte in solution upon addition of SDS was also examined. It was found that 0.16–0.32 mol SDS/mol charged segments on the polyelectrolyte is enough to make the solution slightly turbid.     

Fourier transform spectroscopy using image sensors

Multichannel Fourier transform spectrometers utilizing image sensing devices are reviewed along with the instrumental design concepts. Although the idea itself is fairly simple, a photographic plate in holographic spectroscopy is replaced by an image sensor, there are stringent requirements to be satisfied in order to realize the system for field use. Mainly two types of the instrument, which are characterized by the Sagnac common-path interferometer and the polarization interferometer optics, respectively, are described with regard to their system performances. Examples of the system operation introduced show that Fourier transform spectrometers without mechanical moving parts play an important role in a variety of spectroscopic applications under severe surroundings. In a summary, methods for the resolution enhancement and comments on the signal-to-noise ratio are also included.     

Lattice dynamical study of body-centred tetragonal indium

The phonon dispersion curves, phonon frequency distribution function as well as the lattice specific heat of body-centred tetragonal indium have been deduced using a lattice dynamical model which includes central, angular and volume forces. Six elastic constants, four zone boundary frequencies and an equilibrium condition were used in the evaluation of the force constants. It is shown that this model is elastically consistent and satisfies the symmetry requirements of the lattice, the phonon frequencies of indium deduced from it are in very good agreement with the experimental values of Reichardt and Smith and the theoretical values of Garrett and Swihart, and theθ _D values compare well with the experimental values over a wide temperature range. The apparent discrepancies in the phonon dispersion curves and theθ _D-T curves obtained from deficient models, importance of umklapp processes and the significance of angular forces in the lattice dynamical models are discussed.     

Molecular structure and spectral properties of thionaphthalimides

The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλ_max60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides.     

Stabilization of a high energy molecular conformation by specific intermolecular forces, a novel planar benzylideneaniline system

The system containing six benzylideneanilines (BA) has been studied: Group 1:

Surface forces in wetting films

A short review of various components of surface forces acting in a non-symmetrical system such as wetting films is presented here. Experimental results are compared with modified DLVO theory, which includes, besides dispersion and electrostatic, structural (solvation) forces caused by a change in liquid structure in conditions of confined geometry. The peculiarities of disjoining pressure isotherms and conditions of the film stability of non-polar and polar simple liquids, as well as of aqueous solutions of electrolytes and surfactants, are systematically considered from a historical perspective.     

Effect of Insoluble Surfactants on Drainage and Rupture of a Film between Drops Interacting under a Constant Force

The deformation, drainage, and rupture of an axisymmetrical film between colliding drops in the presence of insoluble surfactants under the influence of van der Waals forces is studied numerically at small capillary and Reynolds numbers and small surfactant concentrations. Constant-force collisions of Newtonian drops in another Newtonian fluid are considered. The mathematical model is based on the lubrication equations in the gap between drops and the creeping flow approximation of Navier–Stokes equations in the drops, coupled with velocity and stress boundary conditions at the interfaces. A nonuniform surfactant concentration on the interfaces, governed by a convection–diffusion equation, leads to a gradient of the interfacial tension which in turn leads to additional tangential stress on the interfaces (Marangoni effects). The mathematical problem is solved by a finite-difference method on a nonuniform mesh at the interfaces and a boundary-integral method in the drops. The whole range of the dispersed to continuous-phase viscosity ratios is investigated for a range of values of the dimensionless surfactant concentration, Peclét number, and dimensionless Hamaker constant (covering both “nose” and “rim” rupture). In the limit of the large Peclét number and the small dimensionless Hamaker constant (characteristic of drops in the millimeter size range) a fair approximation to the results is provided by a simple expression for the critical surfactant concentration, drainage being virtually uninfluenced by the surfactant for concentrations below the critical surfactant concentration and corresponding to that for immobile interfaces for concentrations above it.