Browsing by Author "Flores, Marcos"

Now showing 1 - 9 of 9
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    CHEMOMETRIC OPTIMIZATION OF AN EXTRACTION PROCEDURE USING TARTARIC ACID FOR BUTYLTIN COMPOUNDS FROM SEDIMENT SAMPLES BY GC-PFPD
    (2015) Bravo, Manuel A.; Flores, Marcos; Parra, Sonnia; Quiroz, Waldo; Maxwell, Paulette; Mester, Zoltan
    In this study a simple extraction procedure was developed to minimize the sulfur interferences on the determination of butyltin in sediment samples based on extraction with tartaric acid solution. The optimal conditions were determined using an experimental design methodology and these were achieved using a solution of tartaric acid (0.5 M) with methanol (30 % v/v) for 12 hours in an orbital shaker. This protocol could be followed by a liquid-liquid extraction and this organic phase can be analyzed directly by gas chromatography with pulsed flame photometric detection (GC-PFPD) without any further cleanup due to interferences from elemental sulfur were completely eliminated. The accuracy of the procedure was verified analyzing two reference materials (CRM) (BCR-646, freshwater sediment and PACS-2, marine sediment) and comparing the results to the certified values, the optimized method produced satisfactory results certified values in the CRMs. Finally, harbour sediment samples were analyzed in order to evaluate the suitability of the method for organotin control in complex environmental samples containing high concentrations of sulfur compounds.
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    Determination of the Conformational Preference of para-Aminobenzoic Acid on Vanadium Pentoxide Surface: An XPS and DFT Study
    (2021) Dietrich, Fabian; Fernandez, Juan; Hevia, Samuel; Cisternas, Eduardo; Flores, Marcos
    Self-assembled monolayers are a promising opportunity to control the electrochemical reactions taking place on electrodes of lithium-ion batteries. Such control is relevant to diminish the aging process and to improve the performance of these energy storage devices. From this point of view, the adsorption of para-aminobenzoic acid on vanadium pentoxide, an attractive high-capacity cathode material, is investigated with the combination of experimental angle-resolved X-ray photoelectron spectroscopy as well as dispersion-corrected density functional calculations. Our results show that the molecules prefer a lyingdown or up-standing configuration depending on their concentration. The comparison between experiment and simulation indicates a high coverage of the surface and hence the formation of a self-assembled monolayer of up-standing molecules.
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    Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy
    (2023) Montero, Cecilia; Ramirez, Cristian Gino; Munoz, Lisa; Sancy, Mamie; Azocar, Manuel; Flores, Marcos; Artigas, Alfredo; Zagal, Jose H.; Zhou, Xiaorong; Monsalve, Alberto; Paez, Maritza
    Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.
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    Effect of thiol adsorption on the electrical resistance of copper ultrathin films
    (2024) Gray, Gabriel; Marin, Francisca; del Campo, Valeria; Gonzalez-Fuentes, Claudio; Correa-Puerta, Jonathan; Flores, Marcos; Segura, Rodrigo; Haberle, Patricio; Henriquez, Ricardo
    The impact of thiol adsorption on thin copper films, covered with a copper oxide layer, was investigated using electrical resistance measurements at various stages: during film growth, aging, exposure to air, and immersion in thiol solutions. Thin copper films (20 nm) were thermally evaporated, with variations in substrate temperature (RT, 330 and 390 K). Films deposited at 330 K exhibited the smallest percolation thickness and aging rates due to their compact morphology, showcasing lower surface roughness and correlation length. Exposure to air led to the formation of a Cu2O 2 O layer on the film surface. Subsequent immersion in a dodecanethiol solution in ethanol resulted in a resistance increase, ranging from 0.1 % to 0.4 %. This change was dependent on the substrate temperature, with the largest difference observed at 330 K. This observation suggests that samples grown at this temperature exhibited the highest electron-surface scattering. Moreover, by depositing a chromium surfactant layer, the impact of this scattering mechanism was amplified, leading to a resistance increase of up to 1.2 %. Mayadas-Shatzkes theory provided a good description of these resistance changes. The negatively charged S-head of the adsorbed thiols alters the electric field experienced by conduction electrons in the Cu2O/Cu 2 O/Cu interface, modifying the electron-surface scattering.
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    Improving the interaction between aluminum surfaces and polymer coatings
    (2019) Muñoz, Lisa; Pineda Parra, Fabiola Makarena; Martínez, Carola; Sancy, Mamié; Urzúa, Marcela; Flores, Marcos; Encinas, María V.; Paez, Maritza A.
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    In-situ hydrogenated V2O5 thin films: Study of the structural dynamics and their behavior as Li-ion batteries cathode
    (2024) Briceno, Mackarena; Villarroel, Roberto; Zambrano-Mera, Dario; Fernandez, Juan; Flores, Marcos; Rojas-Saez, Nicols; Lisoni, Judit; Hevia, Samuel; Espinoza-Gonzalez, Rodrigo
    This investigation focuses on a one-step preparation method to produce hydrogenated V2O5 thin films by controlling the atmosphere of the DC reactive magnetron sputtering process. An increasing hydrogen flux during the film deposition promotes the formation of defects such as oxygen vacancies and hydroxyl sites in the oxide matrix. The hydrogenated samples were tested as cathodes in Li-ion batteries and exhibited lower charge capacities but superior stability to cycling compared to pristine V2O5 film. These results pave the way to prepare hydrogenated transition metal oxide thin films by a simple route without further thermal procedures and affordable conditions.
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    Protective Effect of Red Algae (Rhodophyta) Extracts on Essential Dietary Components of Heat-Treated Salmon
    (2021) Ortiz-Viedma, Jaime; Aguilera, Jose M.; Flores, Marcos; Lemus-Mondaca, Roberto; Jose Larrazabal, Maria; Miranda, Jose M.; Aubourg, Santiago P.
    Salmon paste contains nutritious components such as essential fatty acids (EPA, DHA), vitamin E and astaxanthin, which can be protected with the addition of red algae extracts. Phenolic extracts were prepared with an ethanol: water mixture (1:1) from the red seaweeds Gracilaria chilensis, Gelidium chilense, Iridaea larga, Gigartina chamissoi, Gigartina skottsbergii and Gigartina radula, obtained from the Pacific Ocean. Most algae had a high content of protein (>7.2%), fiber (>55%) and beta-glucans (>4.9%), all expressed on a dry weight basis. Total polyphenols (TP), total flavonoids (TF), antioxidant (DPPH, FRAP) and antibacterial power of the extracts were measured. In addition, the nutritional components of the algae were determined. Results showed that the content of TP in the six algae varied between 2.6 and 11.3 mg EAG/g dw and between 2.2 and 9.6 for TF. Also, the extracts of G. skottsbergii, G. chamissoi, G. radula and G. chilensis showed the highest antiradical activity (DPPH, FRAP). All samples exhibited a low production of primary oxidation products, and protection of the essential components and the endogenous antioxidants tocopherols and astaxanthin, particularly in the case of G. skottsbergii, G. chamissoi, G. radula and G. chilensis. Furthermore, all algae had inhibitory activity against the tested microorganisms, coincident with their antioxidant capacity. Results show that the extracts may have future applications in the development and preservation of essential dietary components of healthy foods.
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    Pulsed laser deposition of carbon films in low pressure neutral gas background
    (2012) Guzmán Olivos, Fernando Alfredo; Ruiz Araya, Hugo Marcelo; Favre Domínguez, Mario; Hevia, Samuel; Bhuyan, Heman; Chuaqui, Hernán; Wyndham, Edmund; Flores, Marcos
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    The effect of electron-surface scattering and thiol adsorption on the electrical resistivity of gold ultrathin films
    (2017) Henríquez, Ricardo; Del Campo, Valeria; González Fuentes, Claudio; Correa Puerta, Jonathan; Moraga, Luis; Flores, Marcos; Segura Segura, Rodrigo; Donoso, Sebastián; Marín, Francisca; Bravo, Sergio; Häberle, Patricio