Person: Barragán García, Vicenta María
Universidad Complutense de Madrid
Faculty / Institute
Estructura de la Materia, Física Térmica y Electrónica
Now showing 1 - 10 of 56
PublicationSalt diffusion through cation-exchange membranes in alcohol-water solutions(Elsevier Science BV, 2009-01-12) Izquierdo Gil, María Amparo; Barragán García, Vicenta María; Godino Gómez, María Paz; García Villaluenga, Juan Pedro; Ruiz Bauzá, Carlos; Seoane Rodríguez, BenjamínThe salt flow through several commercial cation-exchange membranes separating two NaCl alcohol-water solutions with the same alcohol concentration, but different NaCl concentration was investigated. Homogeneous (Nafion-115) and heterogeneous (MK-40 and CR65-AZL-412) membranes were used in this work. The integral permeability coefficient was determined from the temporal evolution of the concentration in the dilute solution. The results showed that the integral permeability coefficient depends on both the solution alcohol concentration and the type of alcohol. It is observed that this dependence is function of the membrane structure. In general, for the heterogeneous membranes, the integral permeability coefficient is less sensible to alcohol concentration than for the homogeneous membrane at low and intermediate values of the alcohol percentage in the solutions. PublicationOn Current Dependence of the Electroosmotic Permeability in Ion-Exchange Membranes(Elsevier Science BV, 1994-10-10) Barragán García, Vicenta María; Ruiz Bauzá, Carlos; Mengual Cabezón , Juan IgnacioThe apparent electro-osmotic permeability, W, of three ion-exchange membranes has been obtained under different experimental conditions. The behaviour of W as a function of the current density, I, shows the following characteristics: (i) at sufficiently low values of I, the apparent electro-osmotic permeability decreases when the current density increases; (ii) at an intermediate values of I, a local maximum appears; and (iii) at the highest values of I, the apparent electro-osmotic permeability seems to approach a roughly constant value. The value of I at which the local maximum takes place is very close to the so-called limiting current density. PublicationOn the methanol-water electroosmotic transport in a Nafion membrane(Elsevier Science BV, 2004-06-15) Barragán García, Vicenta María; Ruiz Bauzá, Carlos; García Villaluenga, Juan Pedro; Seoane Rodríguez, BenjamínElectroosmosis experiments through a Nafion membrane have been performed using methanol–water KCl solutions in different experimental situations. The influence on the electroosmotic transport of the percentage of methanol on solvent at different electrolyte concentrations has been studied. The experimental results show that the presence of methanol on the solutions affects strongly to the electroosmotic flow. From the current–voltage curves determined for this membrane system, the limiting currents were obtained at different volume percentages of methanol. The values obtained decrease with increasing the percentage of methanol and a minimum value seems to be reached at certain percentage of alcohol. PublicationExperimental determination of the streaming potential across cation-exchange membranes with different morphologies(Elsevier, 2016) García Villaluenga, Juan Pedro; Somovilla, Pilar; Barragán García, Vicenta María; Izquierdo Gil, María AmparoLiquid uptake and streaming potential have been determined in aqueous sodium chloride solutions for five different commercial sulfonated polymer cation-exchange membranes. The selected membranes have distinct morphologies and electrochemical properties. Differences in the liquid uptake properties of the membranes have been found, which have been analysed on the basis of the structure and the chemical properties of the membranes. In most of the membranes analyzed, the higher the liquid content of the membranes, the lower the effective concentration of fixed charges in the membranes. The streaming potential across the membranes increases linearly with the established pressure difference, and it is larger in heterogeneous membranes than in homogeneous ones. In general, the higher the membrane liquid content, the higher the streaming potential across the membranes. PublicationEstimation of the temperature of a radiating body by measuring the stationary temperatures of a thermometer placed at different distances(IOP Publishing, 2016-07) Barragán García, Vicenta María; García Villaluenga, Juan Pedro; Izquierdo Gil, María Amparo; Pérez Cordón, RafaelThis paper presents a novel method for determining the temperature of a radiating body. The experimental method requires only very common instrumentation. It is based on the measurement of the stationary temperature of an object placed at different distances from the body and on the application of the energy balance equation in a stationary state. The method allows one to obtain the temperature of an inaccessible radiating body when radiation measurements are not available. The method has been applied to the determination of the filament temperature of incandescent lamps of different powers. PublicationSwelling properties of alkali-metal doped polymeric anion-exchange membranes in alcohol media for application in fuel cells(Pergamon-Elsevier Science Ltd, 2016-08-24) Lain, L.; Barragán García, Vicenta MaríaSwelling properties of four commercial anion-exchange membranes with different structure have been analyzed in several hydro-organic media. With this target, the liquid uptake and the surface expansion of the membranes in contact with different pure liquids, water and alcohols (methanol, ethanol and 1-propanol), and with water alcohol mixtures with different concentrations have been experimentally determined in presence and in absence of an alkaline medium (LiOH, NaOH and KOH of different concentrations). The alkali-metal doping effect on the membrane water uptake has also been investigated, analyzing the influence of the hydroxide concentration and the presence of an alcohol in the doping solution. The results show that the membrane structure plays an essential role in the influence that alcohol nature and alkaline media has on the selective properties of the membrane. The heterogeneous membranes, with lower density, show higher liquid uptakes and dimensional changes than the homogeneous membranes, regardless of the doping conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. PublicationEffect of Unstirred Solution Layers on Electroosmotic Permeability of Cation-Exchange Membranes(Academic Press Inc Elsevier Science, 1994-12) Barragán García, Vicenta María; Ruiz Bauzá, Carlos; Mengual Cabezón, Juan IgnacioElectro-osmotic fluxes of water through two cation-exchange membranes have been measured under different experimental conditions. The influence of unstirred solution layers adjoining the membrane surfaces on the obtained values has been studied both theoretically and experimentally A model has been developed which gives quantitative information about the concentration polarization effects on the electro-osmotic fluxes. The theoretical predictions are compared to the experimental results, and the accordance may be considered satisfactory. PublicationFluid flow modeling in a sulfonated cation-exchange membrane(John Wiley & Sons Inc, 2009-11-05) García Villaluenga, Juan Pedro; Barragán García, Vicenta María; Izquierdo Gil, María Amparo; Godino Gómez, María Paz; Seoane Rodríguez, Benjamín; Ruiz Bauzá, CarlosLiquid permeation measurements of water, methanol, and 2-propanol were carried out using a commercial cation-exchange membrane Nafion-117 (perfluorinated polyethylene with pendant ether-linked side chains terminated with sulfonated groups). The experimental permeation data are treated and analyzed using the capillary model, leading to the determination of equivalent pore radius of the membrane structure. PublicationWater uptake and salt transport through Nafion cation-exchange membranes with different thicknesses(Pergamon-Elsevier Science Ltd, 2012) Izquierdo Gil, María Amparo; Barragán García, Vicenta María; García Villaluenga, Juan Pedro; Godino Gómez, María PazThe water uptake of different aqueous salt solutions in different Nafion membranes, and the salt transport through those membranes under the driving force of a concentration gradient, have been studied. These experiments have been performed by using the following salts: lithium chloride, sodium chloride, potassium chloride and cesium chloride. Different homogeneous Nafion membranes, NF111, NF112, NF115 and NF117, have been used in this work, with the aim of studying the membrane thickness influence. It has been observed that the membrane water uptake increases with the membrane thickness and decreases with the size of the cation. The integral permeability coefficient has been determined from the time evolution of the salt concentration in the dilute solution. The results show that the integral permeability coefficient decreases with the membrane thickness. In general, the influence of the type of electrolyte on the integral permeability coefficient is not significant for the membranes with larger thickness (that is, NF115 and NF117). Average apparent cation transport number has been determined for the same salt solutions, and from that membrane apparent permselectivity has been estimated. In general, in membranes with large thickness, the average apparent cation transport number increases with the cation size. Finally, from fluxes and membrane potentials membrane negative ionic permeabilities have been determined finding also that they decrease with membrane thickness. Salt diffusion coefficient has been also determined from membrane negative ionic diffusion coefficient. PublicationOn the electrokinetic characterization of charged polymeric membranes by transversal streaming potential(Pergamon-Elsevier Science Ltd., 2021-08-10) Barragán García, Vicenta María; García Villaluenga, Juan Pedro; Izquierdo Gil, María Amparo; Kristiansen, K. R.The effect of a transmembrane pressure on the electrokinetic properties of different polymeric charged membranes is analysed. Electrokinetic characterization can involve the application of increasing or decreasing pressure differences over a membrane sample. The aim of this work is to study whether the transmembrane pressure application during the measurement process to determine the zeta potential and the intrinsic permeability of polymeric membranes causes a membrane irreversible change. It is a relevant issue in membrane technology, because electrokinetic properties are used to analyse the viability and performance of ion-exchange membranes processes in practical applications. We show that polymeric membranes can be affected by a transmembrane pressure application. This influence does not affect surface char ge distribution of the polymeric membranes, but it can strongly affect the membrane structure. (c) 2021 Elsevier Ltd. All rights reserved.