Persona:
Rubio Álvarez, Miguel Ángel

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ORCID
0000-0002-4210-0443
Fecha de nacimiento
Proyectos de investigación
Unidades organizativas
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Apellidos
Rubio Álvarez
Nombre de pila
Miguel Ángel
Nombre

Filtros

2020 - 20212
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Fecha de finalización: 2021 × Fecha de inicio: 2020 ×

Resultados de la búsqueda

Mostrando 1 - 2 de 2
  • Miniatura
    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 Ángel
    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.
  • Miniatura
    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, Óscar
    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.