365 research outputs found

    Development of Flame Retardant and Antibacterial Dual Functionalised Flexible Polyurethane Foam

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    Flexible Polyurethane foam (PUF), with its unique properties, such as lightweight and softness, has been utilised extensively. Nevertheless, owing to the intrinsic high flammability and low ignition temperature, PUF-associated fire risks are always a concern. During PUF’s combustion, excessive heat and toxic gases can be generated, threatening the health and life of human beings and causing huge property loss. Consequently, improving the flame retardancy of the PUF is of importance. Later, the global COVID-19 pandemic broke out in 2019, leading to the public’s increased awareness of maintaining good hygiene conditions. Since PUF products are frequently in contact with humans daily, rendering the PUF with bacterial-killing properties should also be addressed. This dissertation delivers studies on introducing flame retardancy to the PUF via a surface engineering method named the layer-by-layer (LbL) assembly. Due to the consequent COVID-19 situation, this thesis expands the investigations to endow the PUF with antibacterial performances. Preliminary research on fabricating a newly emerged two-dimensional material called MXene (Ti3C2) and chitosan (CH) as flame retardants (FRs) to impart fire safety performances to the PUF was conducted. With only 6.9 wt.% mass added to the PUF, unprecedented fire resistance and smoke suppression properties were received. It was revealed that the FR mechanism was ascribed to the hybrid coating’s excellent barrier and carbonisation effects. Further investigations on improving the PUFs’ biodegradability identified synergistic effects between the MXene with the CH and phytic acid, demonstrating the great potential for reducing the toxicity and improving the eco-friendliness of the PUFs. Additionally, this thesis analysed the FR and antibacterial dual-functionalised PUFs. The synthesised MXene, CH, and silver ion hybridised coating endows the foam with exceptional bactericidal properties with decreases of 99.7 % in gram-negative bacteria and 88.9 % in gram-positive bacteria compared with the unmodified counterpart. Excellent flame retardancy possessed by the dual-functionalised PUFs was discovered. The compatibility of the two functional coatings was evaluated and confirmed. The results manifest the great potential for eradicating the fire risks of PUFs and providing traditional PUF products with antibacterial properties, further expanding PUF’s applications

    Porous carbon fibers derived from PAN-based block copolymers

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    Mención Internacional en el título de doctorDurante años, los materiales porosos de carbono han suscitado un gran interés para su uso en innumerables aplicaciones tecnológicas, debido a sus excelentes propiedades fisicoquímicas y su elevada superficie específica. Estos materiales han demostrado tener un elevado potencial especialmente en aplicaciones relacionadas con el medioambiente y la energía debido a su alta capacidad para adsorber distintas especies, incluyendo gases, moléculas orgánicas y/o iones metálicos. En particular, las fibras de carbono porosas, PCFs por sus siglas en inglés (Porous Carbon Fibers), con una porosidad controlada y jerarquizada han captado una atención significativa en los últimos años, ya que combinan las ventajas de materiales macro−, meso− y microporosos, lo que las convierte en excelentes candidatas para aplicaciones de adsorción y energía, entre otras. Las PCFs ofrecen una estructura de carbono continua que combina alta conductividad, altos valores de áreas superficiales y densidades muy bajas. Concretamente, en lo que respecta a su uso como materiales para electrodos de supercondensadores, las PCFs presentan algunas ventajas sobre los carbones activos, que son los materiales comúnmente utilizados como electrodos en este tipo de dispositivos. Estas fibras de carbono pueden emplearse idealmente como electrodos sin el uso de aglutinantes o aditivos conductores. Además, para esta aplicación específica, el desarrollo de PCFs con una estructura de poros jerarquizada es especialmente interesante, ya que los mesoporos facilitan la difusión de iones hacia los microporos confinados en las regiones internas del material. Por lo tanto, se consigue incrementar el área de superficie accesible a los iones de electrolito, que se traduce en una mayor capacidad de almacenamiento y con ello se incrementa el rendimiento electroquímico. Destaca el uso de copolímeros en bloque, BCPs por sus siglas en inglés (Block copolymers), como materiales molde o plantilla para la obtención de PCFs, debido a su capacidad para autoensamblarse y separarse en microfases, lo que da lugar a múltiples morfologías. Mediante el empleo de un bloque de sacrificio compuesto por un polímero térmicamente degradable y otro bloque como fuente de carbono, es posible controlar las estructuras de carbono generadas, en términos de volumen, tamaño y forma de los poros. Ajustando la fracción volumétrica del bloque de sacrificio, la interacción entre los bloques y/o el grado de polimerización del copolímero es posible modificar el número, tamaño y forma de los poros generados después de la carbonización del material plantilla. Esta tesis analiza el uso de copolímeros en bloque como precursores para obtener fibras de carbono porosas. Se sintetizaron copolímeros con pesos moleculares definidos, a partir de una polimerización radical controlada (RAFT), basados en poliacrilonitrilo (PAN) y diferentes bloques de sacrificio, como poliestireno (PS) y poli(tert−butil acrilato) (PtBA), que dieron lugar a fibras con distintas propiedades fisicoquímicas. Se ha estudiado el comportamiento de autoensamblaje y separación de fases de los copolímeros durante el tratamiento térmico, así como el tamaño del poro y su distribución después de la pirólisis. La obtención de las fibras porosas se llevó a cabo mediante una técnica simple, versátil, y fácilmente escalable, el electrohilado. Mediante la pirólisis del bloque de sacrificio se obtuvieron fibras de carbono con estructuras de poro jerarquizadas, diámetros estrechos y varias formas y tamaños dependiendo de la naturaleza del bloque de sacrificio y el grado de polimerización. Asimismo, se estudiaron diferentes parámetros que influyen en las propiedades capacitivas y el comportamiento electroquímico de las PCFs. Entre ellos se consideraron la incorporación de heteroátomos (nitrógeno y azufre) y nanopartículas con actividad redox (nanopartículas de magnetita). Las PCFs derivadas de un copolímero en bloque de poliestireno y poliacrilonitrilo (PS−b−PAN), se activaron/doparon con urea y tiourea como precursores de heteroátomos de N y N/S, respectivamente. Estos procesos permitieron obtener PCFs co−dopadas sin comprometer los valores de área superficial y mostrando un aumento de la capacitancia. Por último, se presenta un estudio preliminar de la incorporación de nanopartículas de magnetita (MNPs) con actividad redox en la estructura de las fibras de carbono porosas (PCFs), y su influencia en la microestructura y la porosidad. Para ello, se introdujeron nanopartículas de magnetita en bajas concentraciones en la matriz del copolímero en bloque (PtBA−b−PAN), y posteriormente se utilizó esa dispersión como precursor de electrohilado en la fabricación de las fibras. Se obtuvieron PCFs con una porosidad y rendimiento electroquímico mejorados, en comparación con las fibras fabricadas sin la adición de nanopartículas. En resumen, este trabajo de tesis tiene como objetivo investigar el comportamiento de los copolímeros de bloque basados en poliacrilonitrilo como precursores para la producción de fibras de carbono porosas. En particular, se pretende estudiar las variaciones en los parámetros que influyen en la separación de fases, lo que a su vez permitirá explorar nuevas vías para modular el tamaño y la forma de los poros. Además, a través de la caracterización electroquímica de los materiales generados se analiza el impacto en el rendimiento electroquímico de las variaciones en el área de superficie específica, la distribución del tamaño de los poros y las funcionalidades de la superficie.For years, porous carbon materials have attracted wide interest for their use in countless technological applications, due to their excellent physicochemical properties and their high specific surface area. These materials have shown a high potential, especially for environmental and energy−related applications, due to their ability to adsorb different species, including gases, organic molecules and/or metal ions. In particular, porous carbon fibers (PCFs) with a well−controlled and hierarchical porosity have attracted significant attention recently, since they combine the advantages of macro−, meso− and microporous materials, making them excellent candidates for adsorption and energy applications, among others. PCFs offer a continuous carbon structure that combines high conductivity, high surface area values, and very low densities. Specifically, concerning their use as electrode materials for supercapacitor, PCFs present some advantages over active carbons, which are commonly used as electrodes in these devices. These carbon fibers can ideally be used as self−standing electrodes without using binders or conductive additives. Furthermore, for this specific application, the development of PCFs with a hierarchical pore structure is especially interesting, since the mesopores facilitate the ion−diffusion towards the micropores confined in the internal regions of the material. Therefore, the surface area accessible to electrolyte ions is increased, which translates into a higher storage capacity and thus increases the electrochemical performance. The use of block copolymers (BCPs) as template materials for obtaining PCFs stands out due to the ability of block copolymers to self−assemble and separate into microphases, producing miscellaneous morphologies. By using a sacrificial block composed of a thermally degradable polymer and another block as a carbon source, it is possible to control the carbon structures produced in terms of pore volume, size, and shape. Adjusting the volume fraction of the sacrificial block, the interaction between the blocks and/or the overall degree of polymerization of the copolymer allows to modify the number, size and shape of the pores generated after carbonization of the template. This thesis analyzes the use of block copolymers as precursors to obtain porous carbon fibers. Copolymers with defined molecular weights were synthesized using controlled radical polymerization (RAFT), based on polyacrylonitrile (PAN) and different sacrificial blocks, such as polystyrene (PS) and poly(tert−butyl acrylate) (PtBA), resulting in fibers with different physicochemical properties. The self−assembly and phase separation behavior of block copolymers during thermal treatments, as well as the pore size and distribution after pyrolysis, have been studied. PCFs were obtained using a simple, versatile, and easily scalable technique, electrospinning. By pyrolysis of the sacrificial block, carbon fibers with hierarchical pore structures, narrow diameters, and various shapes and sizes were obtained, depending on the nature of the sacrificial block and the degree of polymerization. Different parameters influencing the capacitive properties and electrochemical behavior of the obtained PCFs were also studied. Among them, the introduction of heteroatoms (nitrogen and sulfur) and redox active nanoparticles (magnetite nanoparticles) were considered. PCFs derived from a polystyrene and polyacrylonitrile block copolymer (PS−b−PAN) were activated/doped with urea and thiourea as N and N/S heteroatom precursors, respectively. These processes allowed to obtain co−doped PCFs without compromising surface area values and showing an increase in capacitance. Finally, a preliminary study is presented based on the addition of magnetite nanoparticles (MNPs) with redox activity in the structure of porous carbon fibers (PCFs), and its influence on the microstructure and porosity. For this purpose, magnetite nanoparticles were introduced in low concentrations into the block copolymer matrix (PtBA−b−PAN), and this dispersion was subsequently used as an electrospinning precursor to produce fibers. PCFs with improved porosity and electrochemical performance were obtained, compared to fibers produced without the addition of nanoparticles. In summary, this thesis aims to investigate the behavior of polyacrylonitrile−based block copolymers as precursors to produce PCFs. In particular, it is intended to study the variations in the parameters that influence phase separation, allowing to explore new ways of modulating the size and shape of the pores. In addition, through the electrochemical characterization of the generated materials, the impact on electrochemical performance of variations in the specific surface area, pore size distribution, and surface functionalities is analyzed.This project has been financed through PIPF scholarship (2019) from the same University and the project PID2021−125302NB−I00 from the Spanish Ministry of Science and Innovation.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidenta: Pilar Herrasti González.- Secretaria: María Crespo Ribadeneyra.- Vocal: Juan José Vilatela Garcí

    Design and validation of experimental methods for probing foam formation dynamics and cellular structure

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    The present thesis focuses on the development of new experimental techniques to study the process-structure-properties relationship in polymeric foams. To achieve this objective rigid polyurethane (RPU) foams were studied. Methodologies have been developed to investigate the synthesis of RPU foams from complementary rheological, physicochemical and structural points of view. To validate the potential of the methods, the effect of different catalyst and blowing agent concentrations on the synthesis of these foams has been systematically studied. As a result of this research, new methods of characterisation of the synthesis process have been obtained at laboratory level, these are based on Dynamic Mechanical Analysis (DMA), Shear Rheology, as well as X-ray tomography and X-ray radioscopy. Furthermore, the development and application of these techniques has allowed to understand the effect of micrometric Silica Aerogel particles on the synthesis, cellular structure and thermal insulation properties of RPU foams reinforced with these particles. The joint evaluation of the reaction kinetics, polymer matrix development and cell structure of RPU foams has identified new ways for the future improvement and optimisation of RPU-Aerogel composite materials with great potential to replace traditional thermal insulators. The present thesis is part of the research activities carried out in the CellMat Laboratory of the Department of Condensed Matter Physics of the University of Valladolid and has been supervised by Prof. Dr. Miguel Ángel Rodríguez-Pérez, director of this laboratory and professor at the University of Valladolid. This thesis has been written as a compendium of eight publications, five of which have already been published in international journals. In addition, this thesis meets the requirements to be accredited with an International Mention.La presente tesis se centra en el desarrollo de nuevas técnicas experimentales para estudiar la relación proceso-estructura-propiedades en las espumas poliméricas. Para alcanzar este objetivo se estudiaron principalmente espumas de poliuretano rígido (RPU). Se han desarrollado metodologías que permiten investigar la síntesis de las espumas de RPU desde puntos de vista complementarios, reológico, fisicoquímicos y estructural. Para validar el potencial de los métodos se ha estudiado de forma sistemática el efecto de distintas concentraciones de catalizador y agente espumante en la síntesis de estas espumas. Como resultado de esta investigación se han podido obtener nuevos métodos de caracterización a nivel de laboratorio del proceso de síntesis, basados en Análisis Mecánico Dinámico (DMA), Reología de Cizalla, así como tomografía y radioscopía de rayos X. Además, el desarrollo y aplicación de estas técnicas ha permitido comprender el efecto de partículas micrométricas de Aerogel de Silice en la síntesis, estructura celular y propiedades de aislamiento térmico de espumas de RPU reforzadas con dichas partículas. La evaluación conjunta de las cinética de reacción, desarrollo de la matriz polimérica y de la estructura celular de las espumas de RPU ha permitido identificar vías para la mejora y optimización futura de materiales compuestos de RPU-Aerogel con gran potencial para sustituir a los aislantes térmicos tradicionales. La presente tesis es parte de las actividades de investigación desarrolladas en el Laboratorio CellMat del Departamento de Física de la Materia Condensada de la Universidad de Valladolid y ha sido supervisada por el Prof. Dr. Miguel Ángel Rodríguez-Pérez, director de este laboratorio y catedrático de la Universidad de Valladolid. Esta tesis se ha escrito como compendio de ocho publicaciones, cinco de las cuales ya han sido publicadas en revistas internacionales. Además, esta tesis reúne los requerimientos para ser acreditada con Mención Internacional.Escuela de DoctoradoDoctorado en Físic

    Environmental Effects of Stratospheric Ozone Depletion, UV Radiation, and interactions with Climate Change: 2022 Assessment Report

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    The Montreal Protocol on Substances that Deplete the Ozone Layer was established 35 years ago following the 1985 Vienna Convention for protection of the environment and human health against excessive amounts of harmful ultraviolet-B (UV-B, 280-315 nm) radiation reaching the Earth’s surface due to a reduced UV-B-absorbing ozone layer. The Montreal Protocol, ratified globally by all 198 Parties (countries), controls ca 100 ozone-depleting substances (ODS). These substances have been used in many applications, such as in refrigerants, air conditioners, aerosol propellants, fumigants against pests, fire extinguishers, and foam materials. The Montreal Protocol has phased out nearly 99% of ODS, including ODS with high global warming potentials such as chlorofluorocarbons (CFC), thus serving a dual purpose. However, some of the replacements for ODS also have high global warming potentials, for example, the hydrofluorocarbons (HFCs). Several of these replacements have been added to the substances controlled by the Montreal Protocol. The HFCs are now being phased down under the Kigali Amendment. As of December 2022, 145 countries have signed the Kigali Amendment, exemplifying key additional outcomes of the Montreal Protocol, namely, that of also curbing climate warming and stimulating innovations to increase energy efficiency of cooling equipment used industrially as well as domestically. As the concentrations of ODS decline in the upper atmosphere, the stratospheric ozone layer is projected to recover to pre-1980 levels by the middle of the 21st century, assuming full compliance with the control measures of the Montreal Protocol. However, in the coming decades, the ozone layer will be increasingly influenced by emissions of greenhouse gases and ensuing global warming. These trends are highly likely to modify the amount of UV radiation reaching the Earth\u27s surface with implications for the effects on ecosystems and human health. Against this background, four Panels of experts were established in 1988 to support and advise the Parties to the Montreal Protocol with up-to-date information to facilitate decisions for protecting the stratospheric ozone layer. In 1990 the four Panels were consolidated into three, the Scientific Assessment Panel, the Environmental Effects Assessment Panel, and the Technology and Economic Assessment Panel. Every four years, each of the Panels provides their Quadrennial Assessments as well as a Synthesis Report that summarises the key findings of all the Panels. In the in-between years leading up to the quadrennial, the Panels continue to inform the Parties to the Montreal Protocol of new scientific information

    Towards COP27: The Water-Food-Energy Nexus in a Changing Climate in the Middle East and North Africa

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    Due to its low adaptability to climate change, the MENA region has become a "hot spot". Water scarcity, extreme heat, drought, and crop failure will worsen as the region becomes more urbanized and industrialized. Both water and food scarcity are made worse by civil wars, terrorism, and political and social unrest. It is unclear how climate change will affect the MENA water–food–energy nexus. All of these concerns need to be empirically evaluated and quantified for a full climate change assessment in the region. Policymakers in the MENA region need to be aware of this interconnection between population growth, rapid urbanization, food safety, climate change, and the global goal of lowering greenhouse gas emissions (as planned in COP27). Researchers from a wide range of disciplines have come together in this SI to investigate the connections between water, food, energy, and climate in the region. By assessing the impacts of climate change on hydrological processes, natural disasters, water supply, energy production and demand, and environmental impacts in the region, this SI will aid in implementation of sustainable solutions to these challenges across multiple spatial scales

    Feature Papers in Electronic Materials Section

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    This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

    Advances in Transmission Electron Microscopy for the Study of Soft and Hard Matter

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    This book provides readers with some examples of advanced applications of electron microscopy on organic and inorganic specimens, highlighting out how new original approaches could provide a deeper understanding of the properties of matter and how a transmission electron microscope is not only a microscope but also a flexible tool for tailoring experiments, properly suited, to the issue of interest
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