We address a problem of fundamental importance in the physics of interfaces, which is central to the description of multiphase fluid dynamics. This work is important to study interfaces in systems such as polymer melts and solutions, where velocity jumps have been observed and interpreted as a manifestation of slip. This is in violation of classical interfacial conditions that require continuity of velocity and has been remedied in the literature via use of ad hoc models, such as the so-called Navier slip condition. This paper suggests that it is possible to obviate completely the need for such an approach. Instead, we show that one simply requires knowledge of the density field and the molar fraction of the fluid components and the dependence of the viscosity on the density. This information can be obtained easily through molecular dynamics simulations.

Cs is the most well known catalyst used in negative ion sources for fast neutral beam generation employed in nuclear fusion, where the element is evaporated and deposited on Mo surfaces forming non permanent films. In this paper the interaction of Cs with Mo under conditions of interest for negative ion sources is studied using different methods. Cs-Mo potential has been characterized starting from high level electronic calculations for two atoms. Mo-Mo and Mo-Cs potentials are based on new fits of the literature data. Density functional theory calculations on a reduced cell are used to determine the adsorption energy of Cs on Mo for different sites. Good reproduction of experimental results, when available, is achieved (e.g. Mo crystal data, Cs 2 dissociation energy) and new results for the evaporation energy of Cs from Mo surfaces, CsMo dissociation energy, adatom geometry etc. are reported and tabulated. A functional expression of the Cs-Mo[0 0 1] interaction potential is proposed based on these ab-initio results. The use of this potential is illustrated by classical MD calculations for the morphology for Cs partial layers on Mo[0 0 1]. Calculations show that the interaction between Cs and the surface leads to peculiar morphology of Cs partial layers, to be considered in future studies of Cs role in negative ion sources as well as in the ongoing quest to alternative catalyzers.

The Griffith‐Ley oxidation of alcohols to aldehydes and ketones is performed with either RuCl3 ⋅ (H2O)x or a highly stable, well‐defined ruthenium catalyst and with cheap trimethylamine N‐oxide (TMAO) as the oxygen source. The use of n‐heptane as the solvent, which forms a second phase with TMAO and a part of the alcohol, allows the reactions to be performed with a minimum amount of catalyst. This results in high local concentrations and thus to very rapid conversions. Detailed quantum chemical calculations suggest, that the Griffith‐Ley oxidation not necessarily requires high oxidation states of ruthenium but can also proceed with RuII/RuIV species.

No abstract

Mechanical properties are very important when choosing a material for a specific application. They help to determine the range of usefulness of a material, establish the service life, and classify and identify materials. The size effect on mechanical properties has been well established numerically and experimentally. However, the role of the size effect combined with boundary and loading conditions on mechanical properties remains unknown. In this paper, by using molecular dynamics (MD) simulations with the state-of-the-art ReaxFF force field, we study mechanical properties of amorphous silica (e.g., Young’s modulus, Poisson’s ratio) as a function of domain size, full-/semi-periodic boundary condition, and tensile/compressive loading. We found that the domain-size effect on Young’s modulus and Poisson’s ratio is much more significant in semi-periodic domains compared to full-periodic domains. The results, for the first time, revealed the bimodular and anisotropic nature of amorphous silica at the atomic level. We also defined a “safe zone” regarding the domain size, where the bulk properties of amorphous silica can be reproducible, while the computational cost and accuracy are in balance.

Abstract.The classical boundary conditions at flat liquid-liquid interfaces are continuity of the velocity and of the tangential component of stress; for curved interfaces, one also demands that the jump in the normal stress at the interface is balanced by the product of the interfacial tension and curvature. While these conditions are widely accepted, and are often used at the macro scale, the recent interest in micro and nano-fluidics challenges their validity. At molten polymerpolymer interfaces, for instance, it has been consistently shown by direct and indirect measurements that, apparent, velocity jumps exist and can be modelled effectively via a Navier slip condition (NSC). Here, we discuss that if a viscosity, which accounts for the density and mole fraction distributions, is included in the Navier-Stokes equations, we can describe, naturally, and without recourse to ad-hoc models such as the NSC, the velocity profile in the interfacial region separating two fluids. This approach is supported by the observation that there is a relation between apparent slip and density distribution across the interface.

A united atom force field for the homologous series of the poly(oxymethylene) dimethyl ethers (OMEn):OMEn are oxygenates and promising new synthetic fuels and solvents. The molecular geometry of the OMEn, the internal degrees of freedom and their electrostatic properties were obtained from quantum mechanical calculations. To model repulsion and dispersion, Lennard-Jones parameters were fitted to the experimental liquid densities and vapour pressures of pure OMEn (n " 1 -4). The critical properties of OMEn (n " 1 -4) were determined from the simulation data. Additionally, the shear viscosity of pure liquid OMEn is evaluated and compared with literature data. Finally, the solubility of CO 2 in OME2, OME3 and OME4 is predicted using a literature model for CO 2 and the Lorentz-Berthelot combining rules. The results agree well with experimental data from the literature.

The knowledge of transport properties is crucial to design new devices in electronic and biotechnological industries. Due to the fast growth of the processor speed, molecular simulations have become a robust method to calculate the transport properties. In this work, we show numerical methods such as Green–Kubo formalism to estimate transport properties applied to real liquids. We focus on the study of shear viscosity and thermal conductivity of a water (H2O) and triethylamine (C6H15N) solution which has a potential application for heat exchange inside electronic circuits. The radial distribution function and hydrogen-bond analysis have been made at a broad range of temperatures and mole fractions using equilibrium molecular dynamics, and comparisons with experimental data in the literature have been reported.