Person: Blázquez Fernández, Samuel
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First Name
Samuel
Last Name
Blázquez Fernández
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Física
Area
Química Física
Identifiers
7 results
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Now showing 1 - 7 of 7
Item Building a Hofmeister-like series for the maximum in density temperature of aqueous electrolyte solutions.(Journal of Molecular Liquids, 2023) Gámez Márquez, Francisco De Asis; Fernández Sedano Vázquez, Lucía; Blázquez Fernández, Samuel; Troncoso, Jacobo; Vega De Las Heras, CarlosThe temperature of the maximum in density (TMD) at room pressure is experimentally evaluated for aqueous solutions of a set of halides containing F−, Cl−, Br−, I−, Li+, Na+, K+, Rb+, Cs+ and Mg2+ at a 1 m concentration. The measurements were performed by monitoring the density- temperature profiles and tracking the temperature-dependent position of the meniscus, in a capillary glass tube. Adding salts diminishes the TMD of the solutions with respect to pure water, being the magnitude of the change dependent on the nature of the electrolyte. The experimental values of the shift in the TMD can be split into individual ion contributions. From this information we were able to establish a rank of ions (i.e. a Hofmeister-like series) according to their efficiency in shifting down the TMD. The experimental results are also compared to simulation values obtained via Molecular Dynamics using the Madrid-2019 force field that assigns non-integer charges for the ions and is parametrized for the TIP4P/2005 water model. Finally, since the TMD is a fingerprint property of water, we will discuss the impact of ions on this maximum in relation with the way different ions modify the structure of water.Item Solubility of Methane in Water: Some Useful Results for Hydrate Nucleation(The Journal of Physical Chemistry B, 2022) Grabowska, Joanna; Blázquez Fernández, Samuel; Sanz García, Eduardo; Zerón, Iván M.; Algaba, Jesús; Míguez, José Manuel; Blas, Felipe J.; Vega de las Heras, CarlosIn this paper, the solubility of methane in water along the 400 bar isobar is determined by computer simulations using the TIP4P/Ice force field for water and a simple LJ model for methane. In particular, the solubility of methane in water when in contact with the gas phase and the solubility of methane in water when in contact with the hydrate has been determined. The solubility of methane in a gas–liquid system decreases as temperature increases. The solubility of methane in a hydrate–liquid system increases with temperature. The two curves intersect at a certain temperature that determines the triple point T3 at a certain pressure. We also determined T3 by the three-phase direct coexistence method. The results of both methods agree, and we suggest 295(2) K as the value of T3 for this system. We also analyzed the impact of curvature on the solubility of methane in water. We found that the presence of curvature increases the solubility in both the gas–liquid and hydrate–liquid systems. The change in chemical potential for the formation of hydrate is evaluated along the isobar using two different thermodynamic routes, obtaining good agreement between them. It is shown that the driving force for hydrate nucleation under experimental conditions is higher than that for the formation of pure ice when compared at the same supercooling. We also show that supersaturation (i.e., concentrations above those of the planar interface) increases the driving force for nucleation dramatically. The effect of bubbles can be equivalent to that of an additional supercooling of about 20 K. Having highly supersaturated homogeneous solutions makes possible the spontaneous formation of the hydrate at temperatures as high as 285 K (i.e., 10K below T3). The crucial role of the concentration of methane for hydrate formation is clearly revealed. Nucleation of the hydrate can be either impossible or easy and fast depending on the concentration of methane which seems to play the leading role in the understanding of the kinetics of hydrate formation.Item Melting points of water models: Current situation(Journal of Chemical Physics, 2022) Blázquez Fernández, Samuel; Vega De Las Heras, CarlosBy using the direct coexistence method, we have calculated the melting points of ice Ih at normal pressure for three recently proposed water models, namely, TIP3P-FB, TIP4P-FB, and TIP4P-D. We obtained Tm = 216 K for TIP3P-FB, Tm = 242 K for TIP4P-FB, and Tm = 247 K for TIP4P-D. We revisited the melting point of TIP4P/2005 and TIP5P obtaining Tm = 250 and 274 K, respectively. We summarize the current situation of the melting point of ice Ih for a number of water models and conclude that no model is yet able to simultaneously reproduce the melting temperature of ice Ih and the temperature of the maximum in density at room pressure. This probably points toward our both still incomplete knowledge of the potential energy surface of water and the necessity of incorporating nuclear quantum effects to describe both properties simultaneously.- Project number: PIMCD378/23-24
Item Innovación sobre la docencia y evaluación del laboratorio de Química Física I(2024) Omiste Romero, Juan José; Ahijado Guzmán, Rubén; Blázquez Fernández, Samuel; Caselli, Niccolo; Díaz Blanco, Cristina; Guerrero Martínez, Andrés; Hernández Díaz, María Yolanda; Labrador Páez, Lucía; Marggi Poullaín, Sonia; Pulido Lamas, Cintia; Sánchez Benítez, Francisco Javier; Sola Reija, Ignacio; Suardíaz Delrío, Reynier; Izquierdo Ruiz, Fernando; Lobato Fernández, Álvaro; Sánchez González, Julia Item On the computation of electrical conductivities of aqueous electrolyte solutions: Two surfaces one property(Journal of Chemical Theory and Computation, 2023) Blázquez Fernández, Samuel; Fernández Abascal, José Luis; Lagerweij, Jelle; Habibi, Parsa; Dey, Poloumy; Vlugt, Thijs; Moultos, Othonas; Vega De Las Heras, CarlosIn this work, we have computed electrical conductivities at ambient conditions of aqueous NaCl and KCl solutions by using the Einstein-Helfand equation. Common force fields (charge q =±1 e) do not reproduce the experimental values of electrical conductivities, viscosities and diffusion coefficients. Recently, we proposed the idea of using different charges to describe the Potential Energy Surface (PES) and the Dipole Moment Surface (DMS). In this work, we implement this concept. The equilibrium trajectories required to evaluate electrical conductivities (within linear response theory) were obtained by using scaled charges (with the value q =±0.75 e) to describe the PES. The potential parameters were those of the Madrid-Transport force field, which describe accurately viscosities and diffusion coefficients of these ionic solutions. However, integer charges were used to compute the conductivities (thus describing the DMS). The basic idea is that although the scaled charge describes the ion-water interaction better, the integer charge reflects the value of the charge that is transported due to the electric field. The agreement obtained with experiments is excellent, as for the first time electrical conductivities (and the other transport properties) of NaCl and KCl electrolyte solutions are described with high accuracy for the whole concentration range up to their solubility limit. Finally, we propose an easy way to obtain a rough estimate of the actual electrical conductivity of the potential model under consideration using the approximate Nernst-Einstein equation, which neglects correlations between different ions.Item The Madrid-2019 force field for electrolytes in water using TIP4P/2005 and scaled charges: Extension to the ions F−, Br−, I−, Rb+, and Cs+(Journal of Chemical Physics, 2022) Blázquez Fernández, Samuel; Martín Conde, María; Fernández Abascal, José Luis; Vega De Las Heras, CarlosIn this work, an extension of the Madrid-2019 force field is presented. We have added the cations Rb+ and Cs+ and the anions F−, Br−, and I−. These ions were the remaining alkaline and halogen ions, not previously considered in the Madrid-2019 force field. The force field, denoted as Madrid-2019-Extended, does not include polarizability and uses the TIP4P/2005 model of water and scaled charges for the ions. A charge of ±0.85e is assigned to monovalent ions. The force field developed provides an accurate description of aqueous solution densities over a wide range of concentrations up to the solubility limit of each salt studied. Good predictions of viscosity and diffusion coefficients are obtained for concentrations below 2 m. Structural properties obtained with this force field are also in reasonable agreement with the experiment. The number of contact ion pairs has been controlled to be low so as to avoid precipitation of the system at concentrations close to the experimental solubility limit. A comprehensive comparison of the performance for aqueous solutions of alkaline halides of force fields of electrolytes using scaled and integer charges is now possible. This comparison will help in the future to learn about the benefits and limitations of the use of scaled charges to describe electrolyte solutions.Item Three phase equilibria of the methane hydrate in NaCl solutions: A simulation study(2023) Blázquez Fernández, Samuel; Vega De Las Heras, Carlos; Conde, MaríaMolecular dynamics simulations have been performed to determine the three-phase coexistence temperature for a methane hydrate system in equilibrium with a NaCl solution and a methane gas phase. The direct coexistence technique is used following two approaches, one where the triple coexistence temperature for a given NaCl concentration is narrow down and another where the concentration at a given temperature is equilibrated. In both approaches the results are consistent within the error bars. All simulations were carried out at 400 bar and the range of concentrations explored extends up to a molality of 4 m. TIP4P/2005 for water molecules and a simple Lennard-Jones interaction site for methane were used to simulate the system. Positive deviations from the Lorentz-Berthelot energetic rule have been applied between methane and water (i.e., increasing the attractive interaction between water and methane). Na+ and Cl− ions were described by using the Madrid-2019 scaled charge model. The role played by finite size effects in the calculation of the coexistence line was analyzed by studying a system with larger number of molecules at a given NaCl concentration. Overall, our simulations show that upon NaCl addition to the liquid water phase, a shift in the three-phase equilibrium line to lower temperatures is produced as occurs in the ice-NaCl(aq) system. The depression of the three-phase coexistence line obtained at different concentrations is in a very good agreement with the experimental results.