Persona: Gálvez González, Óscar
Cargando...
Dirección de correo electrónico
ORCID
0000-0003-2963-9599
Fecha de nacimiento
Proyectos de investigación
Unidades organizativas
Puesto de trabajo
Apellidos
Gálvez González
Nombre de pila
Óscar
Nombre
3 resultados
Resultados de la búsqueda
Mostrando 1 - 3 de 3
Publicación Energetics and structures of the tilted phases of fatty acid Langmuir monolayers(Royal Society of Chemistry, 2020) Toledano Sanz, Óscar; Rubio Álvarez, Miguel Ángel; Gálvez González, ÓscarLangmuir monolayers are monomolecular deep films composed of amphiphilic molecules which are typically confined to a water/air interface in a bi-dimensional structure. Due to the important applications in many research areas, they have been studied for many years. Their phase diagrams present several condensed phases, showing untilted or tilted structures at low values of surface pressure. In this paper, we present a novel density functional study on tilted phases of different fatty acid Langmuir monolayers. By means of this study, a further understanding of the physical chemistry properties and the nature of the formation of tilted monolayers can be achieved. Our calculations reveal that, regardless of the number of carbon atoms which form the apolar chain, the transversal (or conventional in the case of untilted phases) unit cell shows similar dimensions, ca. 4.9 × 6.8 Å, which is in fair agreement with the range of the observed data. The energy variation of the unit cell as a function of the inclination of the molecules, reveals an abrupt increase in values larger than 45° and 36° for NN- and NNN-tilt, respectively, in fair agreement with the experimental observation of L2h (NN) and L2′ (NNN) phases of fatty acids. All of the fatty acids explored (from 10 to 19 carbon atoms) yield similar results. Finally, the energetics and structural changes of the monolayer along the variation of the area per molecule, obtained by enlarging in a-, b- or both axes of the untilted unit cell, have been explored. This study reveals that the untilted phases are energetically more stable at low values of area per molecule (high surface concentration), as it is expected. When the area per molecule values are increased, tilted phases (along NN or NNN-direction) with b/a ratio typical of herringbone (HB) or pseudo-herringbone (PHB) structures are found in the lowest energy configurations, which depend on how the distortion of the untilted unit cell is performed. For example, HB structures are the most stable when the molecules tilt along the enlarged axis of the untilted unit cell (a or b), meanwhile unit cell structures characteristic of PHB configurations occur in the opposite cases and at larger values of the area per molecule (low surface concentrations). All these predictions are in good agreement with the GIXD observations of the different phases of the phase diagram of fatty acid Langmuir monolayers.Publicación Melting in two-dimensional systems: Characterizing continuous and first-order transitions(American Physical Society, 2022-03-16) Toledano Sanz, Óscar; Pancorbo Castro, Manuel; Alvarellos Bermejo, José Enrique; Gálvez González, ÓscarThe mechanisms underlying the melting process in bidimensional systems have been widely studied by means of experiments, theory, and simulations since Kosterlitz, Thouless, Halperin, Nelson, and Young elaborated the KTHNY theory. In the framework of this theory, melting is produced by two continuous transitions mediated by the unbinding of local defects and the appearance of an intermediate phase between solid and liquid, called “hexatic.” There are also other competing theories that could explain this process, as, e.g., the formation of grain boundaries (lines of defects), which lead to a first-order transition. In this paper, simulations of systems interacting via the Lennard Jones 6–12 and Morse potentials using the Metropolis Monte Carlo method in the NVT ensemble have been performed to study the effect of the potential shape in the melting process. Additionally, truncated Morse potentials (with only a repulsive part) have been used to investigate the effect of the long-range interactions. Transitions from solid to hexatic phases were found to be continuous for all potentials studied, but transitions from hexatic to liquid phases were found to be either continuous or first order, depending on the thermodynamic conditions and the potential interaction selected, suggesting that melting can be triggered by different mechanisms, like grain boundary formation or defect unbinding. We find that the ratio of defects at the liquid-hexatic or liquid-coexistence phase transitions could determine the nature of these transitions and the mechanism underlying the melting process. The effect of the interaction of particles with their first- and second-nearest neighbors is also discussed.Publicación Prácticas virtuales de Astrofísica basadas en software libre y bases de datos astronómicos(Universidad Nacional de Educación a Distancia (España). Instituto Universitario de Educación a Distancia (IUED), 2019) Williart Torres, Amalia; Gálvez González, ÓscarPara llevar a cabo la evaluación continua en la asignatura «Astrofísica general», optativa de cuarto curso de los grados en Física y Matemáticas, se han ofertado dos prácticas virtuales voluntarias, basadas en el uso de software libre y bases de datos astronómicos. En la primera de ellas se ha usado ALADIN (CDS, 1999), que es un atlas interactivo del universo. Con los datos obtenidos por los estudiantes pudieron obtener los diagramas Hertzprung-Russell de dos cúmulos estelares abiertos. Con la segunda práctica, usando SIMBAD (CDS, 1979), que es una base de datos astronómicos, pudieron comprobar con datos profesionales que se cumple la ley de Hubble y que el universo está expandiéndose. Estas experiencias han permitido al equipo docente evaluar destrezas y competencias relacionadas con la experimentación en Astrofísica.