- Rubio Álvarez, Miguel Ángel

## Persona: Rubio Álvarez, Miguel Ángel

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0000-0002-4210-0443

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Rubio Álvarez

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Miguel Ángel

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Publicación Prácticas de simulación en la asignatura "Teoría de circuitos y electrónica"(Universidad Nacional de Educación a Distancia (España). Instituto Universitario de Educación a Distancia (IUED), 2019) Montoya Lirola, María del Mar; Rubio Álvarez, Miguel ÁngelMás... Se presenta una actividad desarrollada por el equipo docente de la asignatura «Teoría de circuitos y electrónica» con el objetivo de fomentar una mayor participación del estudiante en su proceso de aprendizaje y de desarrollar nuevos métodos de evaluación de los resultados de aprendizaje. La actividad consiste en ofertar un conjunto de prácticas de simulación para su realización de manera voluntaria por parte de los estudiantes. La puesta en marcha de la actividad ha comprendido la elección del software, la realización de un tutorial y de unas tutorías en línea y la elaboración de los guiones de prácticas. La evaluación de los resultados de aprendizaje se lleva a cabo a través de las memorias de prácticas que elaboran los estudiantes y su contribución a la calificación final es de tipo sumativo.Más... Publicación Flow field based data processing for the oscillating conical bob interfacial shear rheometer(American Institute of Physics, 2018-01-01) Pastor Ruiz, Juan Manuel; Tajuelo Rodríguez, Javier; Rubio Álvarez, Miguel ÁngelMás... A rotational rheometer can be used as an interfacial shear rheometer (ISR) by means of proper accessories that allow one to shear fluid-fluid interfaces in a controlled manner. One of the most used accessories, even commercially available, is based on a biconical bob geometry. However, recovering the correct values of the rheological variables is far from trivial. A strategy that has proved to be successful in other ISRs is to properly account for the interface and subphase drags by numerically finding the corresponding flow fields and, then, use an iterative scheme to recover the proper values of the complex Boussinesq number and, consequently, the dynamic surface moduli. Here, we propose to use such a scheme for the biconical bob oscillatory rheometer. We compare our solution with different well known previous approximations, and discuss under which conditions those approximations may lead to errors in the data processing. We have tested the performance of our design and numerical framework on several interfacial systems, comparing the results to those obtained through a magnetic needle rheometer (ISR). We demonstrate that, even for relatively low values of the Boussinesq number, the numerical flow field solution here proposed allows one to precisely reproduce the results obtained by the ISR, while those approximations based on a linear velocity decay at the interface may introduce spurious effects on the calculation of the dynamic surface moduli.Más... Publicación Flow field-based data analysis in interfacial shear rheometry(Elsevier, 2021-02) Sánchez Puga, Pablo; Pastor Ruiz, Juan Manuel; Tajuelo Rodríguez, Javier; Rubio Álvarez, Miguel ÁngelMás... Developments in interfacial shear rheometers have considerably improved the quality of experimental data. However, data analysis in interfacial shear rheometry is still an active field of research and development due to the intrinsic complexity introduced by the unavoidable contact of the interface with, at least, one supporting bulk subphase. Nonlinear velocity profiles, both at the interface and the bulk phases, pervade the system dynamical behavior in the most usual experimental geometries, particularly in the case of soft interfaces. Such flow configurations demand data analysis schemes based on the explicit calculation of the flow field in both the interface and the bulk phases. Such procedures are progressively becoming popular in this context. In this review, we discuss the most recent advances in interfacial shear rheology data analysis techniques. We extensively review some recently proposed flow field-based data analysis schemes for the three most common interfacial shear rheometer geometries (magnetic needle, double wall-ring, and bicone), showing under what circumstances the calculation of the flow field is mandatory for a proper analysis of the experimental data. All cases are discussed starting at the appropriate hydrodynamical models and using the equation of motion of the probe to set up an iterative procedure to compute the value of the complex Boussinesq number and, from it, the complex interfacial viscosity or, equivalently, the complex interfacial modulus. Moreover, two examples of further extensions of such techniques are proposed, concerning the micro-button interfacial shear rheometer and the potential application of interfacial rheometry instruments, together with adapted flow field-based data analysis techniques, for bulk rheometry, particularly in the case of soft samples.Más... 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, ÓscarMás... Langmuir 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.Más... Publicación Shear rheology of fluid interfaces: Closing the gap between macro- and micro-rheology(Elsevier, 2018-09) Guzmán Solís, Eduardo; Pastor Ruiz, Juan Manuel; González Rubio, Ramón; Tajuelo Rodríguez, Javier; Rubio Álvarez, Miguel Ángel; Ortega Coloma, Francisco JavierMás... For many years the determination of the shear viscosity of interfacial layers has been source of strong controversy. This is mainly because different techniques provided different values of such parameter, which leads in many cases to a puzzling interpretation of the experimental results. One possible explanation of this is the non-correct analysis of the hydrodynamic conditions of the measurement and, in particular, the assumption of some approximations that may not be necessarily valid in all cases. The introduction of hydrodynamic consideration in the study of interfacial shear rheology has helped to clarify some of the existing discrepancies between measurements performed using different devices, thus allowing one to establish clearly the viscosity range in which different techniques can operate with enough sensitivity for determining the interfacial shear viscosity. This review puts in perspective the most recent developments on the studies of the interfacial shear rheology of fluid/fluid interfaces, analyzing the strength and weakness of the different approaches.Más... Publicación Red Interactiva de Inteligencia Colectiva para el servicio Exterior venezolano (RINCEX)(2007-06-18) Alves Pérez, Elisabeth; Rubio Álvarez, Miguel ÁngelMás... Publicación Linear shear rheology of aging β-casein films adsorbing at the air/water interface(Elsevier, 2018-02-01) Martínez Pedrero, F.; Sánchez Puga, Pablo; Chulia Jordan, R.; González Rubio, Ramón; Tajuelo Rodríguez, Javier; Ortega Coloma, Francisco Javier; Rubio Álvarez, Miguel ÁngelMás... In this work, the viscoelasticity of fragile β-casein films has been followed using different macro- and microrheological techniques. The modulus of the complex surface viscosity varies with time, allowing for the monitoring of the protein adsorption and annealing. β-casein adsorption creates a soft glassy gel at the interface that experiences an aging process. Macrorheological experiments with multiple probe sizes in addition to microrheological experiments demonstrated the consistency of the surface rheological properties over a broad range of viscosities. Surface pressure measurements were performed to complement the characterization of the processes.Más... Publicación BiconeDrag—A data processing application for the oscillating conical bob interfacial shear rheometer(Elsevier, 2019-06) Sánchez Puga, Pablo; Pastor Ruiz, Juan Manuel; Tajuelo Rodríguez, Javier; Rubio Álvarez, Miguel ÁngelMás... BiconeDrag is a software package that allows one to perform a flow field based data processing of dynamic interfacial rheology data pertaining to surfactant laden air–fluid interfaces obtained by means of a rotational bicone shear rheometer. MATLAB and Python versions of the program are provided. The bicone fixture is widely used to transform a conventional bulk rotational rheometer into an interfacial shear rheometer. Typically, such systems are made of a bicone bob, which is mounted on the rheometer rotor, and a cylindrical cup. Usually, the experiment consists of measuring the response of the interface under an oscillatory stress. The program takes the values of the torque/angular displacement amplitude ratio and phase difference to compute the interfacial dynamic moduli (or complex viscosity) by consistently taking into account the hydrodynamic flow both at the interface and the subphase. This is done by numerically solving the Navier–Stokes equations for the subphase velocity field together with the Boussinesq–Scriven boundary condition at the interface, and no slip boundary conditions elsewhere. Furthermore, the program implements a new iterative scheme devised by solving for the complex Boussinesq number in the rotor’s torque balance equation.Más...