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Solute diffusion in gels: Thirty years of simulations
(Elsevier, 2021-01) Quesada-Pérez, Manuel; Martín-Molina, Alberto
In this review, we present a summary of computer simulation studies on solute diffusion in gels carried out in the last three decades. Special attention is paid to coarse-grained simulations in which the role of steric and electrostatic interactions on the particle diffusion can be evaluated In addition, other important characteristics of particle diffusion in gels, such as the stiffness of the gel structure and hydrodynamic interactions, can be taken into account through coarse-grained simulations. Emphasis is placed on how simulation results help to test phenomenological models and to improve the interpretation interof experimental results. Finally, coarse-gained simulations have also been employed to study the diffusion controlled release of drugs from gels. We believe that scientific advances in this line will be useful to better understand the mechanisms that control the diffusive transport of molecules in a wide variety of biological systems.
Coarse-grained Monte Carlo simulations of nanogel-polyelectrolyte complexes: electrostatic effects
(Royal Society of Chemistry, 2020-02-14) Pérez-Mas, Luis; Martín-Molina, Alberto; Quesada-Pérez, Manuel
Coarse-grained Monte-Carlo simulations of nanogel-polyelectrolyte complexes have been carried out. The results presented here capture two phenomena reported in experiments with real complexes: (i) the reduction in size after absorbing just a few chains and (ii) the charge inversion detected through electrophoretic mobility data. Our simulations reveal that charge inversion occurs if the polyelectrolyte charge is large enough. In addition, the distribution of chains inside the nanogel strongly depends on whether charge inversion takes place. It should also be stressed that the chain topology has little influence on most of the properties studied here.
Coarse-Grained Simulations of Solute Diffusion in Crosslinked Flexible Hydrogels
(ACS Publications, 2022-02-22) Quesada-Pérez, Manuel; Maroto-Centeno, José-Alberto; Ramos-Tejada, María del Mar; Martín-Molina, Alberto
In this work, the longtime diffusion of a solute in a chemically crosslinked and flexible hydrogel is computed from a coarse-grained model of a polymeric network. The effects of different key parameters of this model on diffusion are assessed. The relevance of chain flexibility becomes important by increasing the polymer volume fraction and the solute size. In fact, the solute particle can moderately diffuse in flexible hydrogels even when its diameter is comparable to the mesh size. The diffusion coefficients obtained here are tested by comparing with the previously reported experimental data. A reasonably good agreement between the experiment and simulation is found without requiring any adjustable parameter.
Electrostatic hindrance to diffusion in flexible crosslinked gels: A coarse-grained simulation study
(AIP Publishing, 2023-07-05) Pérez-Mas, Luis; Ramos-Tejada, María del Mar; Martín-Molina, Alberto; Maroto-Centeno, José ALberto; Quesada-Pérez, Manuel
In this work, we study how electrostatic forces slow down the diffusion of solute in flexible gels through coarse-grained simulations. The model used explicitly considers the movement of solute particles and polyelectrolyte chains. These movements are performed by following a Brownian dynamics algorithm. The effect of three electrostatic parameters characterizing the system (solute charge, polyelectrolyte chain charge, and ionic strength) is analyzed. Our results show that the behavior of both the diffusion coefficient and the anomalous diffusion exponent changes upon the reversal of the electric charge of one of the species. In addition, the diffusion coefficient in flexible gels differs significantly from that in rigid gels if the ionic strength is low enough. However, the effect of chain flexibility on the exponent of anomalous diffusion is significant even at high ionic strength (100 mM). Our simulations also prove that varying the polyelectrolyte chain charge does not have exactly the same effect as varying the solute particle charge.
Coarse-grained simulations of diffusion controlled release of drugs from neutral nanogels: Effect of excluded volume interactions
(AIP Publishing, 2020-01-08) Maroto-Centeno, José-Alberto; Quesada-Pérez, Manuel
The primary goal of this work is to assess the effect of excluded volume interactions on the diffusion controlled release of drug molecules from a spherical, neutral, inert, and cross-linked device of nanometric size. To this end, coarse-grained simulations of the release process were performed. In this way, the inner structure and topology of the polymer network can be explicitly taken into account as well. Our in silico experiments reveal that the boundary condition of constant surface concentration is not appropriate for nanogels. In particular, the predictions based on the perfect sink condition clearly overestimate the fraction of drug released. In addition, these simulations provide values for the release exponent that depends on both the diameter of drug molecules and the number of drug molecules loaded in the matrix, which clearly contrasts with the classical prediction of a constant release exponent. Consequently, the widely used classification of drug release mechanisms based on this kinetic exponent must be extended to include new situations.
Revamping Newtonian Gravity
(SCIRP, 2014-06) Eckhardt, D. H.; Garrido Pestaña, J. L.
The nineteenth century’s quest for the missing matter (Vulcan) ended with the publication of Einstein’s General Theory of Relativity. We contend that the current quest for the missing matter is parallel in its perseverance and in its ultimate futility. After setting the search for dark matter in its historic perspective, we critique extant dark matter models and offer alternative explanations—derived from a Lorentz-invariant Lagrangian—that will, at the very least, sow seeds of doubt about the existence of dark matter.
Magnetic fields in the Milky Way neighbouhood as deduced from WARPS in inspiral galaxies
(EDP Sciences, 1991-11) Battaner, E.; Garrido, J.L.; Sánchez-Saavedra, M.L.; Florido, E.
It is shown that warps of spiral galaxies are not randomly oriented in the Milky Way neighbourhood. By adopting a previous model, in which warps are produced by intergalactic magnetic fields, and considering all northern hemisphere warped edge-on NGC spiral galaxies, an analysis of the intergalactic magnetic field in the 100 Mpc neighbourhood of our Galaxy is carried out. At the 100 Mpc scale the magnetic field is still rather homogeneous, having a direction given by (alpha = 289 degrees, delta = 8 degrees), but a characteristic scale of about 25 Mpc is found, inside which the dispersion is very low. The region containing the Virgo Cluster has a direction of the magnetic field different from the direction found in adjacent regions.
Magnetic fields as an alternative explanation for the rotation curves of spiral galaxies
(Springer Nature, 1992-12) Battaner, E.; Garrido, J.L.; Membrado, M.; Florido, E.
The flat rotation curves of spiral galaxies are usually regarded as the most convincing evidence for dark matter. The assumption that gravity alone is responsible for the motion of gas beyond the visible disks of galaxies leads directly to the conclusion that there must be perhaps 10 times as much dark matter as visible matter. Other forces besides gravity are usually neglected, as order-of-magnitude arguments seem to suggest they cannot be important. The existence of dark matter is, however, so important an issue that we believe it is wise to consider other possibilities. Here we argue that an azimuthal magnetic field can carry slightly ionized gas with the general galactic rotation, rendering dark matter unnecessary (a related idea was first proposed by Nelson1). For the illustrative case of M31, a magnetic field of 6 μG is required, and the synchrotron emission of relativistic electrons in this field is compatible with the observations.
On the coherent orientation of spins of spiral galaxies
(EDP Sciences, 1993-04) Garrido, J.L.; Battaner, E.; Sánchez-Saavedra, M.L.; Florido, E.
The method of convergence of planes developed by Battaner et al. (1991, hereafter BGSF) has been used for investigating coherent alignments of rotation axes of spiral galaxies in the Milky Way neighbourhood. Results are contrasted with previous analyses carried out by other means, taking into account that they were not conclusive either to confirm or to reject coherent alignments. Some improvements of the method are described. No evidence for coherent alignments has been found here, with the exception of some zones, in particular that around the Coma supercluster in which the angular momentum vectors tend to be perpendicular to the axis of the Coma supercluster.
The distribution of dark and luminous matter inferred from extended rotation curves
(Oxford University Press, 2015-04) Bottema, R.; Garrido Pestaña, J.L.
A better understanding of the formation of mass structures in the Universe can be obtained by determining the amount and distribution of dark and luminous matter in spiral galaxies. To investigate such matters a sample of 12 galaxies, most with accurate distances, has been composed of which the luminosities are distributed regularly over a range spanning two and a half orders of magnitude. Of the observed high quality and extended rotation curves of these galaxies decompositions have been made, for four different schemes, each with two free parameters. For a `maximum disc fit' the rotation curves can be well matched, yet a large range of mass-to-light (M/L) ratios for the individual galaxies is required. For the alternative gravitational theory of MOND (Modified Newtonian Dynamics) the rotation curves can be explained if the fundamental parameter associated with MOND is allowed as a free parameter. Fixing that parameter leads to a disagreement between the predicted and observed rotation curves for a few galaxies. When cosmologically motivated NFW dark matter haloes are assumed, the rotation curves for the least massive galaxies can, by no means, be reproduced; cores are definitively preferred over cusps. Finally, decompositions have been made for a pseudo-isothermal halo combined with a universal M/L ratio. For the latter, the light of each galactic disc and bulge has been corrected for extinction and has been scaled by the effect of stellar population. This scheme can successfully explain the observed rotations and leads to submaximum disc mass contributions. Properties of the resulting dark matter haloes are described and a ratio between dark and baryonic mass of ∼9 for the least, and of ∼5, for the most luminous galaxies has been determined, at the outermost measured rotation.
Dark Future for Dark Matter
(SCIRP (Scientific Research Publishing Inc.), 2020-01) Eckhardt, D.H.; Garrido Pestaña, J.L.
The prevailing cosmological constant and cold dark matter (LCDM) cosmic concordance model accounts for the radial expansion of the universe after the Big Bang. The model appears to be authoritative because it is based on the Einstein gravitational field equation. However, a thorough scrutiny of the underlying theory calls into question the suitability of the field equation, which states that the Einstein tensor is a constant multiple of the stress-energy tensor when they both are evaluated at the same 4D space-time point. Notwithstanding its venerable provenance, this equation is incorrect unless the cosmic pressure is 0; but then all that remains of the Einstein equation is the Poisson equation which models the Newtonian gravity field. This shortcoming is not resolved by adding the cosmological constant term to the field equation as in the LCDM model, because then pressure is L, so the pressure is a universal constant, not a variable. Numerous studies support the concept of a linearly expanding universe in which gravitational forces and accelerations are negligible because the baryonic mass density of the universe is far below its critical density. We show that such a coasting universe model agrees with SNe Ia luminosity vs. redshift distances just as well or even better than the LCDM model, and that it does so without having to invoke dark matter or dark energy. Occam’s razor favors a coasting universe over the LCDM model.
Analysis of the Patent of a Protective Cover for Vertical-AxisWind Turbines (VAWTs): Simulations of Wind Flow
(MDPI, 2020-09-22) Moleón Baca, Jose Alberto; Gutierrez Montes, Cándido; Expósito González, Antonio Jesús
El uso de energía eléctrica en localizaciones aisladas y en condiciones climáticas extremas es muy complicado si no se quieren usar combustibles fósiles. En las zonas polares, por ejemplo, los vientos fuertes o las pocas horas de sol impiden el uso de placas solares o de aerogenerador convencionales. Así surge la idea de un aerogenerador con cúpula protectora. Este artículo se centró en una de las aplicaciones de este sistema, se realizaron simulaciones que han indicado mejoras significativas en el diseño para su mejor funcionamiento y rendimiento. Los resultados respaldan que esta patente puede ser una buena alternativa para la generación de energía eólica en zonas geográficas con condiciones climáticas extremas o con viento sostenido o racheado fuerte.
Heterogeneities in the Cohesion of the Deposits of the 2021 Tajogaite Eruption of La Palma (Canary Islands, Spain)
(MDPI, 2023-11) Ontiveros-Ortega, Alfonso; Moleón-Baca, Jose Alberto; Abad, Isabel; Sánchez-Gómez, Mario
The present study analyzes the electrical and thermodynamic properties of the volcanic ash deposits from the recent eruption that started on 19 September 2021 in the Cumbre Vieja area on the island of La Palma. This work compares the analysis of the zeta potential and the surface free energy components of representative samples of unaltered tephra deposits with samples affected by the fumarolic activity near the emission zone, where sulfurous vapors were present. The results show that fumarolic activity modifies both the zeta potential and the surface free energy components of volcanic ash, decreasing its surface electrical charge and conferring less hydrophilicity on the deposit. Based on this, the interaction energies between ash particles in an aqueous medium have been calculated, in order to analyze the cohesion of the deposit and, where appropriate, its rheological properties, ending with the analysis of the effect produced by different chemical species on the surface charge and free energy of the ashes, and their influence on the cohesion of the deposit. The results confirm an attractive interaction energy between the ash particles and therefore greater stability to the deposit affected by fumarolic activity.
Cells electric charge analyses define specific properties for cancer cells activity
(Elsevier, 2022-04) Moleon-Baca JA; Ontiveros -Ortega A; Aranega -Jiménez A; Granados-Principal S
The surface electrical charge of cells is conditioned by the ionic medium in which they are immersed. This charge is specific for each cell type and is especially important in tumour cells because it determines their state of aggregation and their adhesion in the different organs. This study analyses the variations in surface charge of cells when pH, electrolytes, and their concentration are modified. The modification of these factors leads to changes in the surface charge of tumour cells; therefore, their states of aggregation and behaviour can be modified. This may even have a use in the prognosis and treatment of various tumours. Some studies conclude that the activity associated with the glycolysis process is accompanied by a change in the surface charge of cells. Notably, there is a high rate of glycolysis in tumours. Our results show that surface charge of cells strongly depends on nature of ionic medium in which they are found, with the valence of the majority ion being the most important factor. When ionic strength was high, the charge decreased dramatically. On the other hand, charge becomes zero or positive in an acidic pH, while in a basic pH, the negative charge increases.
Hydrophobicity and surface free energy to assess spent coffee grounds as soil amendment. Relationships with soil quality
(Elsevier, 2021-01) Cervera-Mata A; Aranda V; Ontiveros -Ortega A; Comino F; Martin-García JM; Vela-Cano M; Delgado G
The aim of this work was to evaluate the effects of spent coffee grounds (SCG), a highly hydrophobic raw material, on the hydrophobicity of two Mediterranean agricultural soils. Physical, chemical, mineralogical and biological soil properties, most of them used to evaluate soil quality, were studied and related to the main hydrophobicity parameters. The in vitro assay was performed with two SCG doses (2.5 and 10%), two soils and two incubation times (30 and 60 days). Hydrophobicity was determined by the water drop penetration time test (WDPT), the contact angle (CA) with H2O, formamide and diiodomethane, and the surface free energy components (SFE) calculated using the Van Oss model. The addition of SCG increased the WDPT, CA and SFE, being the latter which was related to a greater number of soil quality variables. Hydrophobicity was related to lower humus quality index (HQI), and a higher proportion of labile organic matter, as shown by Infrared and UV–vis spectroscopy. An increase in hydrophobicity was related to an improvement of soil physical quality: a high aggregate stability index, saturated hydraulic conductivity, porosity (total and macro), water retention, and a less bulk density. The most critical effect related to the increase in hydrophobicity was the significant decrease in the available water content. The SEM images showed a greater occlusion and stabilization mechanism of the SCG particles incorporated in Vega soil, probably due to its higher content of smectite and carbonates. The appearance of fungal biomineralizations of calcium carbonate is associated with SCG addition and could be considered as an interesting and little studied process of inorganic carbon fixation and secuestration. These results showed that hydrophobicity can afford relevant information that can help to asses soil quality status after an amendment with SCG.
A new approach to triggering mechanism of volcano landslides based on zeta potential and surface free energy balance
(Elsevier, 2018-01) Ontiveros -Ortega A, Plaza I; Calero J, Romero C
The layers of Almagre (iron-rich deposits) from Tenerife Island are the result of thermal metamorphism of soils in contact with lava flow (1073–1273 K). These layers of small thickness relative to the basaltic wash, are interesting for geotechnical study, because the stability of the deposits is determined by the weakest element, in this case Almagre, which acts as a sliding plane. The flow of maritime air over the hillsides of the volcanic islands increases the content of cations in ashes deposits. This modifies the superficial properties of material that composes the substratum. This modification affects the retention of water and the cohesion of material making up the deposit. The results show that the presence of sodium and magnesium increased the hydrophobicity of the material, which had a weak water retention capacity and strong cohesion at basic pH. When there is iron in solution, repulsion between the particles is greater than one obtained with other studied electrolytes. Hence, the deposit is less stable, and Almagre under saturated water conditions constitutes an ideal layer for landslides.
Thermal decomposition of the CaO in traditional lime kilns. Applications in cultural heritage conservation
(Elsevier, 2018-11) Ontiveros-Ortega E, Ruiz-Agudo EM; Ontiveros-Ortega A
It has been the aim of this paper to know the factors that most affect to the process of obtaining the quicklime in traditional lime kilns. To this end, a comparative study has been carried out between two quicklime types, one obtained in traditional lime kiln and another obtained in an industrial lime kiln. On the other hand, two limestone types, commonly used in the production of lime in these kilns, have been calcination in the laboratory. They correspond to an oosparite and oomicritic limestones, traditionally used in the elaboration of limes in the Morón de la Frontera region, Seville (Spain). The samples have been analyzed from the chemical, physical and mineralogical points of view. The calcination process of the limestones and the optimum heating temperature depends of the porosity and crystalline structure original of the limestones. The calcination temperatures, longer residence time and CO2 and steam pressure in the kilns affects the size and porosity of the CaO crystals. The quicklimes with greater volume of pores allow faster access of water to the interior of the material and consequently the lime slaking reaction is less exothermic. The size of the particles CaO affects the rate of the lime slaking reaction, accelerating the reaction when the particles are smaller. The quicklimes calcined in traditional kilns are characterized by greater particle and pore size and greater volume of mesopores.
High varability of interaction energy between volcanic particles: implications for deposit stability.
(Springer Nature, 2023-10-27) Ontiveros Ortega, Alfonso; Calero, Julio; Moleón Baca, Jose Alberto
Landslides on the flanks of stratovolcanoes can significantly modify the structure of the volcano. Macroscopic factors that determine the stability of volcanic deposits are well understood, but the microscopic interactions between particles and their impact on deposit cohesion remain poorly understood. Deposit cohesion is related to the energy of interaction between particles, and its calculation depends on the surficial properties of the eruptive materials. The purpose of this study was to perform a preliminary comparative analysis of the surficial properties of volcanic materials from various tectonic settings, including electrical (zeta potential) and thermodynamic (surface free energy) components and to calculate the total interaction energy between particles under different environmental conditions. We analyzed samples of eruptive materials obtained from volcanic flows characteristic of six active volcanoes (El Hierro, Pico Do Fogo, Vulcano, Stromboli, Mt. Etna, and Deception Island). The results show that deposit cohesion varies among volcanoes and changes drastically with the pH of the medium. Among the volcanic systems investigated, El Hierro (pH = 3) has the most cohesive materials, while Mt. Etna (pH = 8) has the least cohesive materials. Our results suggest that microscopic electrical and thermodynamic properties play a role in the stability of volcanic deposits, and confirm the need for a greater research focus in this area.
Adsorption of Graphene Oxide onto Synthetic Fibers: Experimental Conditions
(Springer Nature, 2018-08-23) Giménez Martín, Elena; Moleón Baca, Jose Alberto; Ontiveros Ortega, Alfonso; Plaza, Iván
Comparative studies on the adsorption capacity of two synthetic fibers, polyamide (PA 66) and polyester (PET) pre-treated with N-cetylpyridinium chloride (PET-NCPCl), towards graphene oxide (GO) have been carried out. The fiber samples were characterized by scanning electron microscopy (FE-SEM) and Raman spectroscopy. The results of adsorption isotherms, kinetics, and zeta potential determinations as a function of the GO concentration, pH, and temperature show that at a low pH of 2.5 and a high temperature of 323 K, almost 99 % of the 75 mg/l GO solution is adsorbed onto PA 66 and 70 % onto the PET-NCPCl fibers. The interaction should be first attributed to electrostatic forces, also the adsorption data exhibited a good fit to the Freundlich isotherm model and the free energy value of 10 kJ/mol was in the range of physical adsorption, which could suggest that the interaction is driven mainly by physical forces. Due to the increasing development of wastewater treatments based on the GO reactivity with metals and cationic contaminants, synthetic fibers coated with GO could be considered an adsorbent for environmental applications.

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