Análisis de la durabilidad de la cubierta plana invertida, a través del estudio de las interacciones e incompatibilidades entre las membranas sintéticas y el poliestireno extrusionado

La cubierta plana invertida se forma, cuando sobre una membrana impermeable se coloca un aislamiento térmico. Estos materiales pueden separarse con capas auxiliares que impiden el contacto directo entre ellos. Muchos de los materiales que forman esta solución constructiva pueden ser polímeros, como lo son algunas membranas impermeables, las capas auxiliares separadoras o el poliestireno extrusionado (XPS). La mayoría de los polímeros son incompatibles entre sí, por lo que en esta tesis se plantea como hipótesis la posibilidad de que se produzcan interacciones e incompatibilidades entre algunos de estos materiales. Por ello se hace una búsqueda bibliográfica y documental de otras investigaciones que pudieran estar relacionadas con el tema, y se estudian y analizan normas y documentación facilitada por fabricantes. Sin embargo, tras consultar toda la bibliografía y documentación que se referencia en esta tesis doctoral, no fue encontrado ningún trabajo de investigación sobre la influencia de la interacción entre los materiales que componen las cubiertas planas invertidas, y de cómo afecta esta a la durabilidad de las mismas. El propósito de esta tesis es el análisis de la durabilidad de la cubierta plana invertida, desde el punto de vista de las interacciones e incompatibilidades que pueden producirse entre los materiales formantes de esta solución constructiva. Además de este objetivo general, se estudian alternativas que puedan prolongar el ciclo de vida de la cubierta plana invertida. Para ello, se desarrolla un plan experimental con el fin de analizar dichas incompatibilidades, y estudiar los factores que las condicionan. Algunos de los resultados obtenidos, muestran que determinadas láminas impermeables utilizadas normalmente para la construcción de cubiertas planas, pueden interactuar con el XPS y sufrir deterioro. El contacto con el mismo, la incorrecta separación, la presión y el calor, son factores determinantes para que se produzca deterioro. Se puede señalar como una de las conclusiones de esta investigación, que la protección térmica que proporciona el XPS a la cubierta plana invertida, puede no ser suficiente (dependiendo del espesor del mismo, y de la ubicación de la cubierta fundamentalmente), para reducir la cantidad de calor que alcanza la línea de contacto entre los materiales, y por tanto paliar las interacciones que se producen. Además, aunque los geotextiles utilizados como capas auxiliares separadoras, en los gramajes por metro cuadrado, recomendados por algunas de las normas reguladoras de este tipo de cubiertas minoran las interacciones, estas siguen produciéndose. ABSTRACT The inverted flat roof is formed from a waterproofing membrane on which the thermal insulation is placed. These materials may be separated with auxiliary layers, which prevent the direct contact between them. Many of the materials forming this constructive solution can be polymers, such as some waterproofing membranes, the auxiliary separating layers, or the extruded polystyrene board (XPS). Most polymers are incompatible, so this thesis hypothesized that interactions and incompatibilities between some of these materials might be possible. Therefore, a literature search, and other documentation that could be related to the topic, are studied and analyzed, as well as, standards and documentation provided by manufacturers. However, after consulting all literature and documents referenced in this dissertation, it was not found any research about the influence of interaction between the materials forming the inverted flat roof, and how this affects to the durability of them. The purpose of this thesis is the analysis of the durability of the inverted flat roof, from the point of view of interactions and incompatibilities may occur between the materials setting up this constructive solution. Along with this general objective, alternatives that can prolong the life cycle of the inverted roof are studied. To get this, an experimental plan is developed, in order to analyze these incompatibilities, and study the factors conditioning them. Some of the results show, that certain normally used waterproofing laminas for building flat roofs, may interact with XPS producing lamina deterioration. Contact, incorrect separation, pressure and heat, are determinant factors for degradation. It can be pointed out, as one of the conclusions of this research, that the thermal protection provided by XPS to the inverted flat roof, cannot be enough (depending on the XPS thickness, and the location of the flat mainly) to reduce the amount of heat that reaches the contact line between materials, and thus to cut down interactions. Furthermore, although geotextiles used as auxiliary separating layers, within the weights per square meter recommended by some of the regulating rules of this type of roofs reduce interactions, these still occur.

Caracterización físico-mecánica del yeso de construcción con adición de residuos de poliestireno extruído y residuos cerámicos

Este trabajo estudia el comportamiento de una matriz de yeso de construcción a la que se le han añadido residuos de construcción y demolición (RCD), residuos de poliestireno extruido (XPS) y residuos cerámicos respectivamente, combinados y en diferentes porcentajes en función del peso del yeso. Los residuos de XPS son producto de una obra en Madrid donde el material fue utilizado como aislamiento térmico y los residuos cerámicos corresponden a trozos de ladrillos toscos encontrados en una obra paralizada en la ciudad de Ávila. Se confeccionaron probetas con porcentajes hasta 3% de XPS y hasta 50% de cerámicos en función del peso del yeso utilizado, como referencia se confeccionaron probetas sin adición de RCD. Fueron ensayadas en laboratorio y se determinaron las características físicas y mecánicas de las mismas. Tras un análisis comparativo se evidencian que la adición de residuos de XPS y residuos cerámicos en conjunto disminuye la densidad seca del material y la absorción de agua por capilaridad, en algunos casos disminuye la conductividad térmica y aumenta la dureza superficial. ABSTRACT: This paper studies the behavior of a building gypsum matrix to which have been added Construction and Demolition waste (CDW), residues of extruded polystyrene (XPS) and ceramic waste respectively, and combined in different percentages depending on the weight of gypsum. XPS waste are the product of a work in Madrid where the material was used as thermal insulation and ceramic waste correspond to pieces of rough bricks found in a paralyzed work in the city of Avila. Specimens were prepared with percentages up to 3% of XPS and up to 50% depending on the weight ceramic gypsum used as reference samples were prepared without addition of CDW. They were tested in laboratory and determined the physical and mechanical characteristics thereof. After a comparative analysis they show that the addition of ceramic waste and waste XPS decreases together dry material density and water absorption by capillary action, in some cases the thermal conductivity decreases and increases surface hardness.

Stimulation of neurite outgrowth using an electrically conducting polymer

Damage to peripheral nerves often cannot be repaired by the juxtaposition of the severed nerve ends. Surgeons have typically used autologous nerve grafts, which have several drawbacks including the need for multiple surgical procedures and loss of function at the donor site. As an alternative, the use of nerve guidance channels to bridge the gap between severed nerve ends is being explored. In this paper, the electrically conductive polymer—oxidized polypyrrole (PP)—has been evaluated for use as a substrate to enhance nerve cell interactions in culture as a first step toward potentially using such polymers to stimulate in vivo nerve regeneration. Image analysis demonstrates that PC-12 cells and primary chicken sciatic nerve explants attached and extended neurites equally well on both PP films and tissue culture polystyrene in the absence of electrical stimulation. In contrast, PC-12 cells interacted poorly with indium tin oxide (ITO), poly(l-lactic acid) (PLA), and poly(lactic acid-co-glycolic acid) surfaces. However, PC-12 cells cultured on PP films and subjected to an electrical stimulus through the film showed a significant increase in neurite lengths compared with ones that were not subjected to electrical stimulation through the film and tissue culture polystyrene controls. The median neurite length for PC-12 cells grown on PP and subjected to an electrical stimulus was 18.14 μm (n = 5643) compared with 9.5 μm (n = 4440) for controls. Furthermore, animal implantation studies reveal that PP invokes little adverse tissue response compared with poly(lactic acid-co-glycolic acid).

Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers

A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single flagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the flagellar motor was determined by measuring the displacement of the laser beam on a quadrant photodiode. The coverslip was mounted on a computer-controlled piezo-electric stage that moved the tether point in a circle around the center of the trap so that the speed of rotation of the motor could be varied. The motor generated ≈4500 pN nm of torque at all angles, regardless of whether it was stalled, allowed to rotate very slowly forwards, or driven very slowly backwards. This argues against models of motor function in which rotation is tightly coupled to proton transit and back-transport of protons is severely limited.

Modulation of Cell Proliferation and Differentiation through Substrate-dependent Changes in Fibronectin Conformation

Integrin-mediated cell adhesion to extracellular matrices provides signals essential for cell cycle progression and differentiation. We demonstrate that substrate-dependent changes in the conformation of adsorbed fibronectin (Fn) modulated integrin binding and controlled switching between proliferation and differentiation. Adsorption of Fn onto bacterial polystyrene (B), tissue culture polystyrene (T), and collagen (C) resulted in differences in Fn conformation as indicated by antibody binding. Using a biochemical method to quantify bound integrins in cultured cells, we found that differences in Fn conformation altered the quantity of bound α5 and β1 integrin subunits but not αv or β3. C2C12 myoblasts grown on these Fn-coated substrates proliferated to different levels (B > T > C). Immunostaining for muscle-specific myosin revealed minimal differentiation on B, significant levels on T, and extensive differentiation on C. Differentiation required binding to the RGD cell binding site in Fn and was blocked by antibodies specific for this site. Switching between proliferation and differentiation was controlled by the levels of α5β1 integrin bound to Fn, and differentiation was inhibited by anti-α5, but not anti-αv, antibodies, suggesting distinct integrin-mediated signaling pathways. Control of cell proliferation and differentiation through conformational changes in extracellular matrix proteins represents a versatile mechanism to elicit specific cellular responses for biological and biotechnological applications.

Isolation and Contraction of the Stress Fiber

Stress fibers were isolated from cultured human foreskin fibroblasts and bovine endothelial cells, and their contraction was demonstrated in vitro. Cells in culture dishes were first treated with a low-ionic-strength extraction solution and then further extracted using detergents. With gentle washes by pipetting, the nucleus and the apical part of cells were removed. The material on the culture dish was scraped, and the freed material was forced through a hypodermic needle and fractionated by sucrose gradient centrifugation. Isolated, free-floating stress fibers stained brightly with fluorescently labeled phalloidin. When stained with anti-α-actinin or anti-myosin, isolated stress fibers showed banded staining patterns. By electron microscopy, they consisted of bundles of microfilaments, and electron-dense areas were associated with them in a semiperiodic manner. By negative staining, isolated stress fibers often exhibited gentle twisting of microfilament bundles. Focal adhesion–associated proteins were also detected in the isolated stress fiber by both immunocytochemical and biochemical means. In the presence of Mg-ATP, isolated stress fibers shortened, on the average, to 23% of the initial length. The maximum velocity of shortening was several micrometers per second. Polystyrene beads on shortening isolated stress fibers rotated, indicating spiral contraction of stress fibers. Myosin regulatory light chain phosphorylation was detected in contracting stress fibers, and a myosin light chain kinase inhibitor, KT5926, inhibited isolated stress fiber contraction. Our study demonstrates that stress fibers can be isolated with no apparent loss of morphological features and that they are truly contractile organelle.

Effects of unique ion chemistry on thin-film growth by plasma–surface interactions

Plasma processing is a standard industrial method for the modification of material surfaces and the deposition of thin films. Polyatomic ions and neutrals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the deposition of polymeric films from fluorocarbon plasmas. In this paper, low energy CF3+ and C3F5+ ions are used to modify a polystyrene surface. Experimental and computational studies are combined to quantify the effect of the unique chemistry and structure of the incident ions on the result of ion-polymer collisions. C3F5+ ions are more effective at growing films than CF3+, both at similar energy/atom of ≈6 eV/atom and similar total kinetic energies of 25 and 50 eV. The composition of the films grown experimentally also varies with both the structure and kinetic energy of the incident ion. Both C3F5+ and CF3+ should be thought of as covalently bound polyatomic precursors or fragments that can react and become incorporated within the polystyrene surface, rather than merely donating F atoms. The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking probabilities, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger species contribute to the deposition of polymeric films from fluorocarbon plasmas. These results indicate that complete understanding and accurate computer modeling of plasma–surface modification requires accurate measurement of the identities, number densities, and kinetic energies of higher mass ions and energetic neutrals.

Brownian flocculation of polymer colloids in the presence of a secondary minimum

Most analyses of Brownian flocculation apply to conditions where London–van der Waals attractive forces cause particles to be strongly bound in a deep interparticle potential well. In this paper, results are reported that show the interaction between primary- and secondary-minimum flocculation when the interparticle potential curve reflects both attractive and electrostatic repulsive forces. The process is highly time-dependent because of transfer of particles from secondary- to primary-minimum flocculation. Essential features of the analysis are corroborated by experiments with 0.80-μm polystyrene spheres suspended in aqueous solutions of NaCl over a range of ionic strengths. In all cases, experiments were restricted to the initial stage of coagulation, where singlets and doublets predominate.

Enzyme-mediated spatial segregation on individual polymeric support beads: application to generation and screening of encoded combinatorial libraries.

Proteolysis of short N alpha-protected peptide substrates bound to polyoxyethylene-polystyrene beads releases selectively free amino sites in the enzyme-accessible "surface" area. The substantial majority of functional sites in the "interior" of the polymeric support are not reached by the enzyme and remain uncleaved (protected). Subsequent synthesis with two classes of orthogonal protecting groups-N alpha-tert-butyloxycarbonyl (Boc) and N alpha-9-fluorenylmethyloxy-carbonyl (Fmoc)-allows generation of two structures on the same bead. The surface structure is available for receptor interactions, whereas the corresponding interior structure is used for coding. Coding structures are usually readily sequenceable peptides. This "shaving" methodology was illustrated by the preparation of a peptide-encoded model peptide combinatorial library containing 1.0 x 10(5) members at approximately 6-fold degeneracy. From this single library, good ligands were selected for three different receptors: anti-beta-endorphin anti-body, streptavidin, and thrombin, and the binding structures were deduced correctly by sequencing the coding peptides present on the same beads.

Applications of EPR with an Emphasis on Tau Fibril Structure

Substances containing unpaired electrons have been studied by electron paramagnetic resonance (EPR) for nearly 70 years. With continual development and enhancement of EPR techniques, questions have arisen regarding optimum method selection for a given sample based on its properties. In this work, radiation defects, natural lattice defects, solid organic radicals, radicals in solution, and spin-labeled proteins were analyzed using CW, pulse, and rapid scan EPR to compare methods. Studies of solid BDPA, EOe in quartz, Ns0 in diamond, and a-Si:H, showed that rapid scan could overcome many obstacles presented by other techniques, cementing rapid scan as an effective alternative to CW and pulse methods. Relaxation times of six nitroxide radicals were characterized from 0.25-34 GHz, guiding synthesis of improved nitroxides for in vivo imaging experiments. Processes contributing to T1 of DPPH in polystyrene were found through variable temperature measurements at X- and Q-band, resolving previously-reported discrepancies in relaxation properties and providing new insight into this commonly-used standard. In the history of EPR, the study of proteins is relatively new. Double electron-electron resonance (DEER) has emerged as a powerful technique for the study of amyloid fibrils, a class of protein aggregates implicated in a number of neurodegenerative disorders. Microtubule-associated protein tau forms fibrils linked to Alzheimerfs disease through seeded conversion of monomer. Self-assembly is mediated by the microtubule binding repeats in tau, and there are either three or four repeats present depending on the isoform. DEER was used to show that filaments of 3R and 4R tau are conformationally distinct and that 4R fibrils adopt a heterogeneous mixture of conformations. Populations of 4R fibril conformations, which were independently validated using a model system, can be modulated by introduction of mutations to the primary sequence or by varying fibril growth conditions. These findings provided unprecedented insights into the seed selection of tau monomers and established conformational compatibility as an important driving force in tau fibril propagation. Lastly, DEER acquisition was improved through addition of paramagnetic metal to spin-labeled protein, decreasing collection time, and through use of a novel spin label with increased T2, thereby lengthening the available acquisition window.

Síntese, caracterização e atividade catalítica de compostos organolantanídeos contendo os ânions metanossulfonato e pentametilciclopentadienil e o ligante pirazinamida

O estudo de compostos organolantanídeos consiste em um dos campos de maior interesse dentro da química organometálica, principalmente devido ao uso potencial como precursores ou catalisadores em reações de hidrogenação, hidroformilação, carbonilação, oxidação e principalmente polimerização de olefinas. Este interesse tem levado diversos grupos de pesquisa a sintetizarem compostos utilizando o ânion ciclopentadienil e seus derivados ligados a íons lantanídeos (III). O presente trabalho tem como objetivo contribuir para a aplicação desses compostos organolantanídeos como catalisadores em reações de polimerização de olefinas. O trabalho envolveu uma etapa de síntese e caracterização de duas classes de compostos organolantanídeos Ln(MS)2Cp*(Ln = Tb e Yb), e Ln(MS)2Cp*PzA (Ln = Sm, Tb e Yb) e uma etapa de estudo da atividade catalítica desses compostos frente a reações de polimerização de etileno, propileno e estireno, utilizando metilaluminoxano como co-catalisador e a caracterização dos polímeros formados. Os compostos sintetizados apresentaram atividade catalítica apenas para polimerização de estireno. O polímero formado, independente do composto organolantanídeo utilizado, foi caracterizado como poliestireno principalmente atático, indicando que a polimerização não é estereoespecífica e apresentou massa molar da ordem de 104 g/mol.

Modelagem estocástica da dispersão axial: aplicação em um reator tubular de polimerização.

Reatores tubulares de polimerização podem apresentar um perfil de velocidade bastante distorcido. Partindo desta observação, um modelo estocástico baseado no modelo de dispersão axial foi proposto para a representação matemática da fluidodinâmica de um reator tubular para produção de poliestireno. A equação diferencial foi obtida inserindo a aleatoriedade no parâmetro de dispersão, resultando na adição de um termo estocástico ao modelo capaz de simular as oscilações observadas experimentalmente. A equação diferencial estocástica foi discretizada e resolvida pelo método Euler-Maruyama de forma satisfatória. Uma função estimadora foi desenvolvida para a obtenção do parâmetro do termo estocástico e o parâmetro do termo determinístico foi calculado pelo método dos mínimos quadrados. Uma análise de convergência foi conduzida para determinar o número de elementos da discretização e o modelo foi validado através da comparação de trajetórias e de intervalos de confiança computacionais com dados experimentais. O resultado obtido foi satisfatório, o que auxilia na compreensão do comportamento fluidodinâmico complexo do reator estudado.

Polimerização em emulsão de estireno em microrreator.

A polimerização em emulsão de estireno em um microrreator Syrris de 250 µL com misturador estático junção \"T\" foi estudada em duas etapas. Primeiro somente a fluidodinâmica deste dispositivo não convencional foi avaliada, depois, foi desenvolvida a reação de polimerização de forma a observar como este fator influencia no sistema. Os experimentos foram realizados procurando se atingir maiores conversões, mas mantendo a estabilidade da emulsão. Foi um trabalho exploratório, portanto se assemelha mais a um processo de evolução (evolutionary process). Foram verificados a partir de qual relação das vazões dos dois fluidos ocorre a formação de gotas, e que com o aumento da vazão da fase contínua, aquosa (Qc), mantendo constante a vazão da fase dispersa (Qd), foi verificado uma diminuição do diâmetro das gotas e um regime de fluxo laminar. Posteriormente, realizou-se a polimerização em emulsão do estireno no microrreator, porém com restrições para altas vazões. Os parâmetros de processo testados foram a proporção Qc e Qd, a temperatura e a concentração do iniciador para então verificar o efeito que a variação destas ocasionam na conversão de monômero, no diâmetro e número de partículas e nas massas moleculares médias. A polimerização foi feita para soma das vazões Qc e Qd da ordem de 100 µ L/min, com 15% de monômero na formulação e com o maior tempo de residência possível de 2,5 minutos. Para maiores concentrações de monômero, acima de 15% foi verificado entupimento do canal do microrreator. A taxa de conversão de monômero aumentou com o aumento da temperatura e com o aumento da concentração do iniciador, mas o maior valor atingido foi de apenas 37% devido ao baixo tempo de residência. Nos casos de maiores taxas de conversão, as massas moleculares obtidas foram as menores conforme o esperado pela teoria. Finalmente, os índices de polidispersão (PDI), obtidos foram da ordem de 2,5 a 3,5.

Nanocompósito de poliestireno reciclado, bentonita sódica e hemi-hidrato de sulfato de cálcio: obtenção e caracterização.

Nesta Tese foram preparados, em solução, filmes híbridos de argila e poliestireno provenientes de copos descartáveis comercializados no mercado brasileiro, com acetato de etila e glicerol. Posteriormente, foi adicionado o Hemi-hidrato de sulfato de cálcio como carga de reforço. Tanto a argila quanto o glicerol, assim como o hemihidrato de sulfato de cálcio, foram utilizados nos percentuais relativos à massa do poliestireno fragmentado correspondendo a 1%,2%, 3%,4%, 5% e 7%. Dos filmes, nos percentuais 3, 4, 5 e 7, exclui-se o percentual de 4% e os demais foram fragmentados e submetidos a extrusão, com resfriamento natural, à seco, produzindo-se grãos com os quais foi avaliado o índice de fluidez e injetados para a moldagem de corpos de prova rígidos. O desempenho dos corpos rígidos, foi comparado com os resultados do HIPS 484, e o GPPS comercializados no mercado brasileiro. Os filmes foram caracterizados por difração de raios X, microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC), além dos testes de resistência à tração, fluorescência de raios X, EDS e FTIR. Amostra do filme, ultrafino, obtido a partir da solução com o percentual de 5% foi observada ao microscópio ótico e no microscópio eletrônico de transmissão, assim como amostras de corpos rígidos microtomizadas. Nos corpos rígidos, além das análises instrumentais citadas, foram avaliadas a resistência à flexão, modulo de flexão, resistência à tração, alongamento e resistência ao impacto Izod. O desempenho sob chama foi avaliado em amostras de filme e também do corpo rígido. Resultados do DRX, e da MET foram coerentes com a bibliografia para nanocompósitos argila-polímero e, associado às respostas dos demais ensaios, indicaram um material de boa qualidade morfológica e boas propriedades mecânicas comparadas ao HIPS 484 e ao GPPS. Sob a chama o material produzido apresentou maior resistência à queima avaliado pela quantidade aparente de material residual para um mesmo tempo sob fogo. Constatou-se, também, uma boa dispersão das cargas na matriz polimérica, assim como uma adequada interação entre os elementos orgânicos e inorgânicos do material, a delaminação parcial da argila e quebra da estrutura do hemi-hidrato. Isto resultou em um bom desempenho mecânico e térmico do compósito que pode ser atribuído, tanto a uma forte influência dos íons metálicos presentes nas cargas inorgânicas, quanto às adições presentes na formulação dos copos descartáveis.

New Methods for Measuring Transient Interactions Between Proteins and Curved Membranes

Variations in the physical deformation of the plasma membrane play a significant role in the sorting and behavior of the proteins that occupy it. Determining the interplay between membrane curvature and protein behavior required the development and thorough characterization of a model plasma membrane with well defined and localized regions of curvature. This model system consists of a fluid lipid bilayer that is supported by a dye-loaded polystyrene nanoparticle patterned glass substrate. As the physical deformation of the supported lipid bilayer is essential to our understanding of the behavior of the protein occupying the bilayer, extensive characterization of the structure of the model plasma membrane was conducted. Neither the regions of curvature in the vicinity of the polystyrene nanoparticles or the interaction between a lipid bilayer and small patches of curved polystyrene are well understood, so the results of experiments to determine these properties are described. To do so, individual fluorescently labeled proteins and lipids are tracked on this model system and in live cells. New methods for analyzing the resulting tracks and ensemble data are presented and discussed. To validate the model system and analytical methods, fluorescence microscopy was used to image a peripheral membrane protein, cholera toxin subunit B (CTB). These results are compared to results obtained from membrane components that were not expected to show an preference for membrane curvature: an individual fluorescently-labeled lipid, lissamine rhodamine B DHPE, and another protein, streptavidin associated with biotin-labeled DHPE. The observed tendency for cholera toxin subunit B to avoid curved regions of curvature, as determined by new and established analytical methods, is presented and discussed.