Ethyl Lauroyl Arginate,an Inherently Multicomponent Surfactant System

Ethyl lauroyl arginate (LAE) is an amino acid-based cationic surfactant with low toxicity and antimicrobial activity. It is widely used as a food preservative and component for food packaging. When stored, LAE decomposes by hydrolysis into surface-active components Nα-lauroyl–l-arginine (LAS) or dodecanoic (lauric) acid. There are only a limited number of reports considering the mechanism of surface activity of LAE. Thus, we analysed the surface tension isotherm of LAE with analytical standard purity in relation to LAE after prolonged storage. We used quantum mechanical density functional theory (DFT) computations to determine the preferred hydrolysis path and discuss the possibility of forming highly surface-active heterodimers, LAE-dodecanoate anion, or LAE-LAS. Applying molecular dynamics simulations, we determined the stability of those dimers linked by electrostatic interactions and hydrogen bonds. We used the adsorption model of surfactant mixtures to successfully describe the experimental surface tension isotherms. The real part surface dilational modulus determined by the oscillation drop method follows a diffusional transport mechanism. However, the nonlinear response of the surface tension could be observed for LAE concentration close to and above Critical Micelle Concentration (CMC). Nonlinearity originates from the presence of micelles and the reorganisation of the interfacial layer.     

Alkali metal halogenides coordination compounds with hexamethylenetetramine

Six coordination compounds: [Li(H₂O)₄]⁺·hmta·Cl^?, [Li(H₂O)₄]⁺·hmta·I^?, [Na(H₂O)₄(hmta)] ²⁺₂ ·2H₂O·2Br^?, [Na(H₂O)₄(hmta)] ²⁺₂ ·2H₂O·2I^?, [K(H₂O)(hmta)I] _n and [Rb(H₂O)(hmta)I] _n , have been synthesized and characterised by IR spectroscopy, thermogravimetry coupled with differential thermal analysis, elemental analysis and X-ray crystallography. Both the sodium compounds are isostructural in a solid state, an isostructurality is also observed between compounds containing potassium and rubidium iodides. The sodium compounds exist as dimers (dinuclear core of the complex ion is created by two sodium cations and two water molecules). The molecules of potassium and rubidium compounds are assembled to the two dimensional hybrid nets. The each potentially multifunctional ligand (the hmta) exists in the outer coordination sphere in lithium compounds, acts in a monodentate mode in sodium compounds and in bidentate-bridging modes in potassium and rubidium compounds. The lithium ions are four coordinated, and the sodium, potassium and rubidium ions are six coordinated. Thermal analyses show that the investigated compounds decompose gradually with the formation of alkali metal halides which, during the further heating, are totally removed or they undergo partial decomposition to oxides.

     

Terahertz spectroscopy of the explosive taggant 2,3-dimethyl-2,3-dinitrobutane

The terahertz spectrum of the crystalline explosive taggant 2,3-dimethyl-2,3-dinitrobutane (C(6)H(12)N(2)O(4)) has been investigated as an alternative means of detecting solid-state explosives. The room-temperature spectrum exhibits two broad absorption features centered at 38.3 and 49.2 cm(-1). Once the sample is cooled to liquid-nitrogen temperatures, the resolution of three additional peaks occurs, with absorption maxima now appearing at 40.1, 47.5, 56.6, 63.9, and 73.6 cm(-1). Solid-state density functional theory simulations, both with and without London force dispersion corrections, have been used for the assignment of the experimental cryogenic THz spectrum to specific molecular motions in the crystalline solid. The B3LYP hybrid density functional paired with the 6-311G(2d,2p) basis set provides an excellent reproduction of the experimental data revealing that the THz spectrum arises from a mixture of intramolecular torsional vibrations localized primarily in the nitro groups and intermolecular lattice vibrations composed of rigid molecular rotations.     

Influence of mass loading on particle-laden turbulent channel flow

Results are presented for the behavior of particle-laden gases in a moderate Reynolds number vertical channel down flow. The effects of mass loading on the gas-phase turbulence and particle concentration are studied. A direct numerical simulation including models of wall-particle interaction is conducted. It is confirmed that particle feedback causes the turbulence intensities to become more non-isotropic as the particle loading is increased. The particle concentration exhibits a maximum close to the wall and a slight increase in the middle of the channel. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Particle-Laden Turbulent Channel Flow and Particle-Wall Interactions

The behavior of particle-laden gases in a turbulent channel flow is studied at moderate Reynolds number. Effects of the wallparticle interaction models on the velocity, statistics, and dispersion of the particles are presented. The results were obtained from a direct numerical simulation with particle feedback on the gas phase. The models were found to considerably influence the studied particle properties. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Forces acting on particles in separated wall‐bounded shear flow

Trajectories of solid particles in laminar and turbulent flow over a backward‐facing step (BFS) were numerically computed by integrating the equation of motion for particles. The various forces acting on the particles [5],[6] were calculated for a variety of flow Reynolds numbers and for different particle characteristics such as the Stokes number and the particle‐to‐fluid density ratio. The investigation was conducted for the distinct flow regimes of the BFS flow separately. Generally, the drag and gravitation were found to be the most significant forces. The lift and history force were the next most important, mostly two orders of magnitude smaller, but in some cases closing up to the other two in importance. The pressure and virtual mass effects were very small for the majority of cases. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)