Comportamiento del SDS localizado en la región interfacial del sistema agua/n-octano. Un estudio usando dinámica molecular

En este trabajo, usando dinámica molecular se determinaron las propiedades interfaciales y el comportamiento del Dodecil Sulfato de Sodio (SDS) ubicado en la región interfacial de los sistemas vacío/agua y agua/n-octano. La tensión interfacial fue estimada con el modelo propuesto por Kirkwood y Buff [23]. A su vez, los espesores de película interfacial fueron determinados usando los criterios 10-90 y 90-90. Además, el área por molécula fue estimado con la variación de la presión superficial en función de la concentración del surfactante. En los sistemas vacío/SDS/agua, el área por molécula del SDS fue obtenida con dos procedimientos diferentes. Los valores fueron 53.3 Å2 y 54.3 Å2, respectivamente. Para los sistemas agua/n-octano y agua/SDS/n-octano, los espesores de película interfacial aumentan en función del número de moléculas de surfactantes presentes en la región interfacial. Los resultados obtenidos son consistentes con datos medidos por experimentación

Exploring the effect of the O -(1-heptylnonyl) benzene sulfonate surfactant on the nature of the linear hydrocarbons/water interface by means of an atomistic molecular dynamics simulation

Using molecular dynamics simulations a systematic study of the binding energy per cross sectional area for the water/n-alkane (hexane, octane, decane, dodecane and tetradecane) interfaces was performed. The effect of the Sodium p-(1-heptylnonyl) benzene sulfonate surfactant, on the adhesion forces of the water/n-hydrocarbon (decane, undecane, dodecane, and tetradecane) interfaces was studied. Scanning of the binding energy per area against n-alkanes shows that the magnitude of this parameter for the surfactant tail-alkane interactions at the interface systematically increases with the chain length of the alkane, whereas it shows a maximum at undecane for the water-surfactant head interactions at the interface. This maximum of head adhesion forces thus agrees with the reported minimum value of the interfacial tension at undecane for the p-(1-heptylnonyl) benzene sulfonate, suggests that for the water/alkane interface it is this trend in surfactant head adhesion at the interface that defines that interfacial tension minimum value

Distribución del 1-butanol y 2-butanol en los sistemas agua/n-octano y agua/Dodecil ´Sulfato de Sodio (SDS)/n-octano usando dinámica molecular. Parte II. Uso de las herramientas gmx-density y gmx-densmap

En este trabajo, la distribución de las moléculas de 1-butanol y 2-butanol en los sistemas agua/n-octano y agua/SDS/n-octano fue determinada usando las herramientas gmx-density y gmx-densmap del programa gromacs con la finalidad de complementar a nivel computacional el comportamiento experimental estos co-surfactantes cuando están localizados en la región interfacial de estos sistemas. Los modelos de energía potencial GROMOS53A6 y SPC fueron utilizados para describir a las moléculas de 1-butanol, 2-butanol, SDS y agua, respectivamente. Estos modelos fueron capaces de predecir las propiedades interfaciales del sistema agua/n-octano y el área por molécula del Dodecil Sulfato de Sodio en la interfaz agua/n-octano de forma consistente. Finalmente, los perfiles y mapas de densidad demuestran que las moléculas de alcohol y SDS coexisten en la región interfacial del sistema agua/n-octano favoreciendo la estabilidad de la monocapa de surfactante y la película interfacial

Exploring the electron density localization in single MoS2 monolayers by means of a localize-electrons detector and the quantum theory of atoms in molecules

The nature of the electron density localization in a MoS2 monolayer under 0 % to 11% tensile strain has been systematically studied by means of a localized electron detector function and the Quantum Theory of atoms in molecules. At 10% tensile strain, this monolayer become metallic. It was found that for less than 6.5% of applied stress, the same atomic structure of the equilibrium geometry (0% strain) is maintained; while over 6.5% strain induces a transformation to a structure where the sulfur atoms placed on the top and bottom layer form S2 groups. The localized electron detector function shows the presence of zones of highly electron delocalization extending throughout the Mo central layer. For less than 10% tensile strain, these zones comprise the BCPs and the remainder CPs in separates regions of the space; while for the structures beyond 10% strain, all the critical points are involved in a region of highly delocalized electrons that extends throughout the material. This dissimilar electron localization pattern is like to that previously reported for semiconductors such as Ge bulk and metallic systems such as transition metals bulk. © 2017 Author(s)

Nature of the Active Sites of Molybdenum-Based Catalysts and Their Interaction with Sulfur- and Nitrogen-Containing Molecules Using the Quantum Theory of Atoms in Molecules and the Molecular Electrostatic Potentia

Density-functional theory (DFT), morphologic, and quantum theory of atoms in molecules (QTAIM) studies of bilayer models of nonhydrogenated MoS2, CoMoS, and NiMoS phases have been performed. The QTAIM calculations have shown that for inactive catalysts, such as MoS2 and Ni3S2, the basins of the outermost atoms of the particles on the exposed surfaces are almost covered by S atomic basins, giving reduced access to the Ni and Mo atoms. In contrast, for very active catalysts, such as NiMoS and RuS2, there are substantial open zones on the outermost S basin, giving considerable access to the metal atoms. Analysis of the electrostatic potential mapping onto the outermost atoms basins reveals soft Lewis acid zones for Ni3S2 and MoS2 and strong Lewis acid zones for NiMoS and RuS2. QTAIM and electrostatic potential calculations on hydrated MoS2-based monolayers have shown that the adsorption strengths (binding energies) of sulfur (H2S, thiophene, dibenzothiophene) and nitrogen (NH3 and acridine) compounds on the exposed metallic sites are related to the Lewis basic-acid interaction of the minima at the molecule and the maxima at the metallic sites, whereas on the so-called BRIM sites, it is the result of the combination of Lewis and Brønsted acidity. The studied nitrogen and sulfur molecules exhibit just one and two lone pairs on the N and S atoms, respectively. In general, N minima ≫ S minima, showing the origin of the larger adsorption of the organonitrogen molecules, except on those metallic sites where both sulfur lone pairs adsorb at two neighboring metal maxima. The present results corroborate and explain the origin of the reported DFT findings

Exploring the electron density localization in MoS2 nanoparticles using a localized-electron detector: Unraveling the origin of the one-dimensional metallic sites on MoS2 catalysts

The nature of the electron density localization in two MoS2 nanoclusters containing eight rows of Mo atoms, one with 100% sulphur coverage at the Mo edges (n8-100S) and the other with 50% coverage (n8-50S) was studied using a localized-electron detector function defined in the local moment representation. For n8-100S, pairs of neighboring S2 dimers cover the edges and the electron density localization function analysis shows the presence of a local triangular-shaped ring zone of highly delocalized electrons along these edges, which corresponds to a good metallic conductor zone. The optimized geometry analysis shows that the Mo-S2 bond length is much longer than that of the Mo-S bonds inside the cluster. The removal of one S atom from each sulphur dimer to create a cluster with 50% coverage produces a general compressive stress on the cluster optimized geometry, which shortens the Mo-S bond length, particularly at the edge. The electron density location function analysis shows that close to the cluster corners, a zone of highly delocalized electron zones with a characteristic semiconductor pattern and broken one-dimensional metallic ring was generated. These results suggest that the Mo-S2 bond elongation produced by the sulphur dimers is similar to a MoS2 monolayer under tensile strain and is the origin of the one-dimensional metallic sites at the Mo-edges. In general, the present findings show excellent agreement with the key features of the reported ambient pressure X-ray photoemission spectra and the corresponding simulated scanning tunneling microscopy images

Predicción del volumen molar y la entalpía molar de vaporización de moléculas orgánicas usando variables determinadas mediante el modelo de apantallamiento tipo conductor (COSMO)

Usando el método de solvatación del modelo de apantallamiento tipo conductor (COSMO) y el método de Amovilli-Mennucci contenido en el programa GAMESS, se estimaron las energías libres de Van der Waals y electrostáticas de moléculas orgánicas en su propio medio dieléctrico. Con estas energías y el volumen de la cavidad del soluto, se diseñaron dos modelos de relación estructura-propiedad (QSPR) para determinar el volumen molar y la entalpía de vaporización a la temperatura de ebullición de las moléculas orgánicas. El mejor modelo obtenido usando el volumen molar presenta una correlación igual a 0,9949 y la correlación del modelo usando la entalpía de vaporización fue 0,[email protected] the method of solvation Conductor-like Screening Model (COSMO) and the method of Amovilli-Menucci GAMESS program content, we estimated the free energies of van der Waals and electrostatic of organic molecules in their dielectric medium. With these energy and volume of the solute cavity, we designed two models of structure-property relationship (QSPR) to determine the molar volume and enthalpy of vaporization to the ebullition temperature of organic molecules. The best obtained model using the molecular volume presents a correlation equal to 0.9949 and the correlation of the model using the enthalpy of vaporization was 0. 9895