Nanocomposites de matriz epoxi: caracterización de la interfase por fluorescencia

La utilización de la espectroscopia de fluorescencia ha demostrado ser una herramienta potente y eficaz para evaluar las propiedades de la interfase en nanocomposites de matriz epoxi. Utilizando nanopartículas de sílice como nanorefuerzo se han preparado diferentes nanocomposites variando el contenido de nanorrefuerzos, cambiando así el aspecto estructural de la interfase con diferentes estados de dispersión. Se han modificado superficialmente las nanopartículas para generar diferentes interacciones carga/matriz para así evaluar su impacto en las propiedades macroscópicas. Los tratamientos superficiales de las nanopartículas de sílice han permitido también localizar un cromóforo en diferentes regiones de la interfase, y estudiar sus propiedades a partir la emisión de fluorescencia. Se ha estudiado la formación de la red termoestable a nivel macroscópico, y a nivel local utilizando la espectroscopia de fluorescencia. Se ha mostrado que la adición de nanopartículas de sílice acelera la reacción de curado a nivel macroscópico. A nivel interfacial, con la información proporcionada por la espectroscopia de fluorescencia, se ha podido apreciar que la reacción de curado ocurre antes en la zona interfacial y de forma más acelerada que en el seno de la matriz y que estos fenómenos dependen de la naturaleza de la interfase. Se ha realizado un estudio de la dinámica de la relajación estructural de la matriz polimérica y de la temperatura de transición vítrea asociada. Se ha demostrado que macroscópicamente existe en estos nanocomposites dos efectos antagonistas sobre la dinámica de las cadenas poliméricas: una restricción de movilidad a nivel de la interfase y un fenómeno de ruptura de la red termoestable que contribuye a aumentar la movilidad segmental. Ambos efectos dependen de la naturaleza de la interfase. La localización del cromóforo en diferentes regiones de la interfase ha permitido determinar su extensión y diferenciar su comportamiento estructural del de la matriz

Towards Hydrazine Based Hydrogen Storage Materials Incorporating Late Transition Metals: a DFT Study

AbstractOur established method of modeling transition metal based H2 storage materials is extended to include the desirable and achievable targets of hydrazine linked Cu(I), Cu(II) and Ni(II). Two coordinate Cu(I) H2 binding site representations bind two H2 molecules through the reversible Kubas interaction with a theoretical maximum storage capacity of 4.27%wt

Fluorescence probes the early formation of network at the interface of epoxy-silica nanocomposite during curing

The effect of surface modified silica on the cure behavior at the interface of epoxy-silica nanocomposites has been analyzed monitoring the fluorescence of the dansyl probe located at different distances from the silica surface by means of molecular tethers. FTIR analysis revealed the catalytic role of the surface hydroxyls, which is modulated by the surface modification. Fluorescence results show that network formation and associated phenomena as gelation and vitrification occurs first at the interface. The exchange of branched species throughout the permeable interface spreads its influence to the whole system until vitrification is reached.Authors are gratefully acknowledged to Spanish Ministerio de Economía y Competitividad for financial support under grant MAT2010-17091

Interfacial characterization of epoxy/silica nanocomposites measured by fluorescence

Artículo publicado en papel: enero 2015 pero disponible online desde 10 noviembre 2014.Fluorescence labeling was used as a tool for the interfacial characterization of nanocomposites. The solvatochromic probe dansyl chloride was employed as interfacial reporter in epoxy/silica nanocomposites. Molecular spacers (organosiloxanes and polyetheramines) of different lengths were used to vary the location of the chromophore at the interface. The steady state and time resolved fluorescent responses reflect a rigid polar interface. Fluorescence changes during heating at a constant rate were analyzed for determining the local glass transition (Tg) at the interface region. The fluorescence results were then compared to the Tg obtained from differential scanning calorimetry and the results showed the existence of a gradient interface of a few nanometers thick having different properties than the bulk matrix. The thickness of this interface is small but its altered dynamics due to strong interactions with the nanofiller spreads its influence throughout the whole matrix.J.C. Cabanelas, C. Antonelli, J. Baselga and B. Serrano gratefully acknowledge Spanish Ministerio de Educación, Cultura y Deporte (MAT2010-17091) for financial support. R. Ozisik acknowledges support from the United States National Science Foundation under Grant No. 1200270

Sodium polymer electrolytes composed of sulfonated polysulfone and macromolecular/molecular solvents for Na-batteries

Polysulfone acidic ionomers have been extensively used as Fuel Cell membranes, mainly because of their mechanical, thermal, chemical and electrochemical stability as well as their excellent film-forming capability. This contribution deals with the development of blends based on polysulfone-sodium sulfonate and macromolecular/molecular solvents, consisting of poly(oxyethylene), POE, and propylene carbonate, PC, respectively. The objectives were to take advantage of both the thermomechanical performances and the macromolecular polyanions provided by the polysulfone ionomer. Combining POE/PC solvents, didn't allow obtaining sufficient blend's conductivities. Nevertheless, the addition of very low amounts of sodium perchlorate led to appreciable conductivities.This work has been supported by Projects funded by the regional government (Comunidad de Madrid through MATERYENER3CM S2013/MIT-2753), the Spanish Government, MICINN (MAT2016-78362-C4-3-R) and Fundación Iberdrola España for the Energy and Environment Research Grants 2016. J-Y Sanchez acknowledges the CONEX Programme, funding received from Universidad Carlos III de Madrid, the European Union’s Seventh Framework Programme for research, technological development and demonstration (Grant agreement nº 600371), Spanish Ministry of Economy and Competitiveness (COFUND2013-40258) and Banco Santander

Nanocrystalline cellulose reinforced poly(ethylene oxide) electrolytes for lithium-metal batteries with excellent cycling stability

Polyethylene oxide (PEO) based polymer electrolytes are still the state of the art for commercial lithium-metal batteries (LMBs) despite their remaining challenges such as the limited ionic conductivity at ambient temperature. Accordingly, the realization of thin electrolyte membranes and, thus, higher conductance is even more important, but this requires a sufficiently high mechanical strength. Herein, the incorporation of nanocrystalline cellulose into PEO-based electrolyte membranes is investigated with a specific focus on the electrochemical properties and the compatibility with lithium-metal and LiFePO$_4$-based electrodes. The excellent cycling stability of symmetric Li||Li cells, including the complete stripping of lithium from one electrode to the other, and Li||LiFePO$_4$ cells renders this approach very promising for eventually yielding thin high-performance electrolyte membranes for LMBs

Molecular probe technique for determining local thermal transitions: The glass transition at Silica/PMMA nanocomposite interfaces

Local glass transition temperatures (Tg) have been measured in the interfaces of solution blended silica/poly(methyl methacrylate) (PMMA) nanocomposites using florescence spectroscopy and compared with Tg measured by differential scanning calorimetry (DSC). It was found that the two types of measurements yielded significantly different information. Combinations of silanes and poly(propylene glycol)-based molecular spacers bound to fluorophores were covalently linked to the surface of the nanoparticles, allowing for variation of the fluorophore response with respect to the distance from the nanofiller surface. Increases in the bulk Tg from the neat PMMA value were found upon the addition of nanofillers, but were independent of the nanofiller concentration when the filler concentration was above 2% by weight. Furthermore, as the size of the grafted molecular spacer was increased, Tg values were found to decrease and approach Tg of the neat PMMA. Owing to variable conformations of the spacers, an effective distribution of fluorophore-silica distances exists, which influences the fluorophores' response to the transition.This research was supported by the National Science Foundation under Grant No. 0500324. Authors from UC3M would like to acknowledge CICYT for financial support (MAT 2007-63722)

Interplay between Conductivity, Matrix Relaxations and Composition of Ca-Polyoxyethylene Polymer Electrolytes

This article also appears in: In Memoriam: Prof. Jean-Michel Savéant.In this report, the conductivity mechanism of Ca2+-ion in polyoxyethylene (POE) solid polymer electrolytes (SPEs) for calcium secondary batteries is investigated by broadband electrical spectroscopy studies. SPEs are obtained by dissolving into the POE hosting matrix three different calcium salts: CaTf2, Ca(TFSI)2 and CaI2. The investigation of the electric response of the synthetized SPEs reveals the presence in materials of two polarization phenomena and two dielectric relaxation events. It is demonstrated that the nature of the anion (i. e., steric hindrance, charge density and ability to act as coordination ligand) and the density of “dynamic crosslinks” of SPEs is fundamental in the establishment of ion-ion/ion-polymer interactions. The long-range charge migration processes occurring along the two revealed percolation pathways of the electrolytes are generally coupled with the polymer host dynamics and depend on the temperature and the anion nature. This study offers the needed tools for understanding Ca2+ conduction in POE-based electrolytes.This work has been supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 829145(FETOPEN-VIDICAT).V. Di Notothanks the University CarlosIII of Madrid for the “Catedras de Excelencia UC3M-Santander” (Chairof Excellence UC3M-Santander)

Colorectal polypectomy and endoscopic mucosal resection: European Society of Gastrointestinal Endoscopy Cascade Guideline

No abstract availabl

International therapeutic guidelines for patients with HCV-related extrahepatic disorders. A multidisciplinary expert statement

Hepatitis C virus (HCV) is both hepatotrophic and lymphotropic virus that causes liver as well extrahepatic manifestations including cryoglobulinemic vasculitis, the most frequent and studied condition, lymphoma, and neurologic, cardiovascular, endocrine-metabolic or renal diseases. HCV-extrahepatic manifestations (HCV-EHMs) may severely affect the overall prognosis, while viral eradication significantly reduces non-liver related deaths. Different clinical manifestations may coexist in the same patient. Due to the variety of HCV clinical manifestations, a multidisciplinary approach along with appropriate therapeutic strategies are required. In the era of interferon-free anti-HCV treatments, international recommendations for the therapeutic management of HCV-EHMs are needed. This implies the need to define the best criteria to use antivirals and/or other therapeutic approaches. The present recommendations, based on qualified expert experience and specific literature, will focus on etiological (antiviral) therapies and/or traditional pathogenetic treatments that still maintain their therapeutic utility