Persona: Gálvez González, Óscar
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Gálvez González
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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 Energetics and structures of the tilted phases of fatty acid Langmuir monolayers(Royal Society of Chemistry, 2020-05-18) Toledano Sanz, Óscar; Rubio, Miguel A.; 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 Energetics and structure of Langmuir monolayers of palmitic acid: a DFT study(Royal Society of Chemistry, 2019-05-08) Toledano Sanz, Óscar; Gálvez González, ÓscarLangmuir monolayers are monomolecular wide films composed of amphiphilic molecules with a bi-dimensional structure typically formed at the air-water interface. They have been studied for many years because these monolayers have important applications in many research fields. Their phases diagram present several condensed phases whose atomic structure is not yet completely known. We present a novel density functional study on palmitic acid dimers and monolayers. Our results reveal that dihydrogen contacts established among alkyl chains play a leading role in the final structure, regarding both dimers and for the arrangement of molecules in the monolayer. In addition, our calculations show that tilted phases at approx. 30o can be formed without significant loss of structure stability, a result that is in agreement with the experimental findings. Different structures for the high pressure phases, S and CS, are proposed here for the first time, being in good greement with the diffraction data available. Furthermore, linear compressibility values also in accordance with previous experimental studies are presented for several structures.Publicación Study of the Crystal Structure and Hydrogen Bonding during Cold Crystallization of Poly(trimethylene 2,5-furandicarboxylate)(American Chemical Society, 2024-02-25) Toledano Sanz, Óscar; Gálvez González, Óscar; Sanz Monasterio, Mikel; García Arcos, Carlos; Rebollar, Esther; Nogales, Aurora; García Gutiérrez, Mari Cruz; Santoro, Gonzalo; Irska, Izabela; Paszkiewicz, Sandra; Szymczyk, Anna; Ezquerra, Tiberio A.; https://orcid.org/0000-0002-2494-3551; https://orcid.org/0000-0002-3604-1512; https://orcid.org/0000-0003-4751-2209; https://orcid.org/0000-0002-5521-1847; https://orcid.org/0000-0002-9670-6395; https://orcid.org/0000-0001-9966-519XHere, we present a detailed description of the in situ isothermal crystallization of poly(trimethylene 2,5-furandicarboxylate)(PTF) as revealed by real-time Fourier transform infrared spectroscopy (FTIR) and grazing incidence wide-angle X-ray scattering (GIWAXS). From FTIR experiments, the evolution of hydrogen bonding with crystallization time can be monitored in real time, while from GIWAXS, crystal formation can be followed. Density functional theory (DFT) calculations have been used to simulate FTIR spectra for different theoretical structures, enabling a precise band assignment. In addition, based on DFT ab initio calculations, the influence of hydrogen bonding on the evolution with crystallization time can be understood. Moreover, from DFT calculations and comparison with both FTIR and GIWAXS experiments, a crystalline structure of poly(trimethylene 2,5-furandicarboxylate) is proposed. Our results demonstrate that hydrogen bonding is present in both the crystalline and the amorphous phases and its rearrangement can be considered as a significant driving force for crystallization of poly(alkylene 2,5-furanoate)s.Publicación Development of polar phases in ferroelectric poly(vinylidene fluoride) (PVDF) nanoparticles(Elsevier, 2023-01-03) Gutiérrez Fernández, Edgar; Sena Fernández, Jose; Rebollar, Esther; Ezquerra, Tiberio A; Hermoso Pinilla, Francisco J.; Sanz, Mikel; Gálvez González, Óscar; Nogales, AuroraFerroelectric polymer nanoparticles of poly(vinylidene fluoride) (PVDF) were prepared by dialysis nanoprecipitation. Particles with mean diameter of 230 nm show piezoelectric response as observed by Piezoresponse Force Microscopy (PFM). The origin of this ferroelectric behavior has been attributed to the presence of ferroelectrically active crystalline phases of PVDF in the nanoparticles (mainly β and γ phases) as demonstrated by differential scanning calorimetry (DSC) and temperature dependent Fourier transform infrared spectroscopy (FTIR) and X ray diffraction. The combination of the preparation method and temperature treatment can provide a method for tuning the ferroelectricity in PVDF homopolymer nanoparticles.Publicación Effects of confinement and vaccination on an epidemic outburst: a statistical mechanics approach(American Physical Society, 2021-09-28) Toledano Sanz, Óscar; Mula, Begoña; Santalla, Silvia N.; Rodríguez Laguna, Javier; Gálvez González, ÓscarThis work describes a simple agent model for the spread of an epidemic outburst, with special emphasis on mobility and geographical considerations, which we characterize via statistical mechanics and numerical simulations. As the mobility is decreased, a percolation phase transition is found separating a free-propagation phase in which the outburst spreads without finding spatial barriers and a localized phase in which the outburst dies off. Interestingly, the number of infected agents is subject to maximal fluctuations at the transition point, building upon the unpredictability of the evolution of an epidemic outburst. Our model also lends itself to testing vaccination schedules. Indeed, it has been suggested that if a vaccine is available but scarce it is convenient to carefully select the vaccination program to maximize the chances of halting the outburst. We discuss and evaluate several schemes, with special interest on how the percolation transition point can be shifted, allowing for higher mobility without epidemiological impact.Publicación Iodide conversion to iodate in aqueous and solid aerosols exposed to ozone(Royal Society of Chemistry, 2020-02-17) Moreno, Carolina; Baeza Romero, María Teresa; Sanz Monasterio, Mikel; Gálvez González, Óscar; López Arza, Vicente; Iann, James C.; Espíldora, Eva; https://orcid.org/0000-0001-6891-4982; https://orcid.org/0000-0002-8390-0949; https://orcid.org/0000-0001-6963-9812; https://orcid.org/0000-0001-6003-4497The aqueous-phase and surface reactions of ozone (O3) with iodide (I−) in/on seawater have been recently found to be a strong atmospheric source of iodine. In addition, ozone also reacts with I− in solid and aqueous sea-salt aerosol. However, the primary products of the heterogeneous reactions of ozone with I− have not been clarified. In this paper, solid and aqueous KI aerosols have been exposed to ozone in an aerosol flow tube system and I− and iodate (IO3−) concentrations have been measured by UV-Vis spectroscopy. The results of these experiments have been combined with a kinetic model to elucidate the primary products of the aqueous and surface reactions. The reaction of ozone with aqueous iodide has been inferred to originate different products depending on whether it occurs at the surface via O3 adsorption (product I2−) or in the aqueous phase via O3 solvation (product IO−). The surface reaction of ozone with solid KI in the presence of water vapor forms KIO3, and other species, which are likely to be gaseous. Although the reactions have been studied in aerosols, the results can be extrapolated to aqueous solutions as well.Publicación Inter and intra molecular dynamics in poly(trimethylene 2,5-furanoate) as revealed by infrared and Broadband Dielectric Spectroscopies(Elsevier, 2023-02-22) Gálvez González, Óscar; Toledano Sanz, Óscar; Hermoso,Francisco Javier; Linares, A.; Sanz Monasterio, Mikel; Rebollar, Esther; Nogales, Aurora; García Gutiérrez, Mari Cruz; Santoro, Gonzalo; Irska, Izabela; Paszkiewicz, Sandra; Szymczyk, Anna; Ezquerra, Tiberio A.Infrared spectroscopy (IR) and Broadband Dielectric Spectroscopy (BDS) experiments have been performed in poly(trimethylene 2,5-furanoate)(PTF) and poly(trimethylene terephthalate)(PTT) below their glass transition temperatures. The BDS experiments reveal a richer inter-molecular dynamic for PTT as characterized by a multimodal β relaxation in contrast with the monomodal one exhibited by PTF. The evolution with temperature of comparable IR absorption bands is very similar for PTF and PTT and shows small shifts in wavenumbers towards lower values, with exception of the band related to the stretching mode of the carbonyl group. In addition, a significant difference appears in the shape of the bands associated with the –Cdouble bondO stretching. While for PTT the absorption feature is comprised of a single component, that for PTF exhibits several components suggesting the presence of hydrogen bonds. This effect may be responsible for the monomodal shape of the β relaxation of PTF since a higher degree of intramolecular coupling between the furan ring and the rest of the monomer is expected. Density Functional Theory (DFT) calculations support the experimental results revealing that as temperature increases an increment of the syn conformations of the 2,5-furandicarboxylic acid (FDCA) moiety is likely to occur in the amorphous state. The energy gain from more stable anti to less stable syn isomers can be compensated by the formation of hydrogen bonds between interchain FDCA moieties in syn conformations. This effect may cause additional hindrance to the intermolecular dynamics of the dielectric β relaxation. It is conceivable that the hindrance exhibited by PTF in both intra and inter-molecular dynamics may play a role in the reduction of gas diffusion and permeability of PTF in comparison with PTT.Publicación Probing structure development in Poly(vinylidene Fluoride) during “operando” 3-D printing by small and wide angle X-ray scattering(Elsevier, 2022-04-10) Ezquerra, Tiberio A.; Nogales, Aurora; García Gutiérrez, Mari Cruz; Rebollar, Esther; Gálvez González, Óscar; Sics, Igors; Malfois, MarcWe have investigated the crystallization of the thermoplastic polymer Poly(vinylidene Fluoride) (PVDF) during “operando” 3D printing Fused Filament Fabrication (FFF). The performance of the 3D printing set-up and the corresponding methodology for performing simultaneous SAXS/WAXS with synchrotron radiation have been discussed. Simultaneous SAXS and WAXS experiments were performed across the printed line with a resolution of 50 μm. The experiments indicate that crystallization is faster at the polymer-air interface than in other points within the printed line. The final crystallinity varies with position being lower at both the interfaces, i.e. polymer-air (13%) and welding zone (11%), while being higher (18%) in the middle part of the printed line. Orientation of the crystalline lamellae is higher at both interfaces, suggesting higher shear rate than in the bulk of the printed line where elongational flow is dominant. The final crystallinity levels in the different locations of the printed line are relatively low, as compared with reported values in melt pressed samples (≈30%), due to the extremely fast crystallization kinetics involved in the solidification of PVDF 3D printed lines. Therefore, it is expected that 3D printed PVDF pieces will exhibit significant structural modifications due to the potential crystallization that eventually will proceed during storage because the glass transition of PVDF is well below room temperature.