Nanoporous PMMA: A novel system with different acoustic properties

The acoustic properties of closed cell nanoporous and microporous poly(methyl methacrylate) (PMMA) foams have been well characterized, showing that nanoporous PMMA exhibit a different absorption coefficient and transmission loss behavior in comparison with microporous PMMA. Experimental differences may be explained by the different wave propagation mechanism in the micro and nanoscale, which is determined by the confinement of both the gas (Knudsen regime) and the solid phases. These results place nanoporous materials as a new class of polymeric porous material with potential properties in the field of acoustics, especially in multifunctional systems requiring a certain degree of soundproofing

Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

Nanocellular polymers are a new generation of materials with the potential of being used as very efficient thermal insulators. It has been proved experimentally that these materials present the Knudsen effect, which strongly reduces the conductivity of the gas phase. There are theoretical equations to predict the thermal conductivity due to this Knudsen effect, but all the models consider an average cell size. In this work, we propose a model to predict the thermal conductivity due to the conduction mechanisms of nanocellular materials with bimodal cellular structures, that is, with two populations of cells, micro and nanocellular. The novelty of our work is to consider not only the average cell size, but the cell size distribution. The predictions of the model are compared with the experimental conductivity of two real bimodal systems based on poly(methyl methacrylate) (PMMA), and it is proved that this new model provides more accurate estimations of the conductivity than the models that do not consider the bimodality. Furthermore, this model could be applied to monomodal nanocellular polymers. In particular, for monomodal materials presenting a wide cell size distribution and at low densities, the model predicts important variations in comparison with the current models in the literature. This result indicates that the cell size distribution must be included in the estimations of the thermal conductivity of nanocellular polymer

Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization

Low-density nanocellular polymers are required to take advantage of the full potential of these materials as high efficient thermal insulators. However, their production is still a challenging task. One promising approach is the use of nanostructured polymer blends of poly(methyl methacrylate) (PMMA) and a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM), which are useful for promoting nucleation but seem to present a severe drawback, as apparently avoid low relative densities. In this work, new strategies to overcome this limitation and produce low-density nanocellular materials based on these blends are investigated. First, the effect of very low amounts of the MAM copolymer is analysed. It is detected that nanostructuration can be prevented using low copolymer contents, but nucleation is still enhanced as a result of the copolymer molecules with high CO2 affinity dispersed in the matrix, so nanocellular polymers are obtained using very low percentages of the copolymer. Second, the influence of the foaming temperature is studied. Results show that for systems in which there is not a clear nanostructuration, cells can grow more freely and smaller relative densities can be achieved. For these studies, blends of PMMA with MAM with copolymer contents from 10 wt% and as low as 0.1 wt% are used. For the first time, the production strategies proposed in this work have allowed obtaining low density (relative density 0.23) nanocellular polymers based on PMMA/MAM blends. Graphical abstrac

Posicionamiento y agrupación de la prensa española: Análisis de contenido de las noticias generadas en la Jornada Mundial de la Juventud 2011

In this paper we present a content analysis regarding the position held by several Spanish newspapers and press agencies concerning an international event; the World Youth Day 2011. Its main purpose is to analyse how different media positioned themselves when informing over such event by analyzing the frequency of negative terms in news pieces. To this end, word frequency analysis was applied to 4,860 news pieces, which were then processed through clustering techniques; Multidimensional Scaling and Hierarchical Ascendant Classification. Clustering analysis sheds light on the position of newspapers and their similarities. Results show differences in coverage and uses of keywords. We will find three main clusters of newspapers appear, according to their editorial lines.El presente trabajo es un análisis de contenido aplicado a las noticias españolas de prensa y agencias relacionadas con la Jornada Mundial de la Juventud. El objetivo principal es analizar cómo se posicionan los medios analizando los términos relacionados con noticias negativas de un total de 4860 noticias, utilizando como fuente la Base de Datos MynewsOnline®. La agrupación se consigue aplicando técnicas estadísticas de Escalamiento Multidimensional y Clasificación Ascendente Jerárquica. Así mismo se describe la producción de noticias por cabeceras y los términos negativos de mayor frecuencia y su posición en el ranking de frecuencias absolutas. Los resultados demuestran desigualdades de cobertura y uso de términos claves. Igualmente se producen tres agrupaciones de conjuntos de periódicos, muy relacionadas con la ideología editorial de sus cabeceras

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed

Nanoporous polymeric materials: A new class of materials with enhanced properties

Producción CientíficaNanoporous polymeric materials are porous materials with pore sizes in the nanometer range (i.e., below 200 nm), processed as bulk or film materials, and from a wide set of polymers. Over the last several years, research and development on these novel materials have progressed significantly, because it is believed that the reduction of the pore size to the nanometer range could strongly influence some of the properties of porous polymers, providing unexpected and improved properties compared to conventional porous and microporous polymers and non-porous solids. In this review, the key properties of these nanoporous polymeric materials (mechanical, thermal, dielectric, optical, filtration, sensing, etc.) are analyzed. The experimental and theoretical results obtained up to date related to the structure–property relations are presented. In several sections, in order to present a more compressive approach, the trends obtained for nanoporous polymers are compared to those for metallic and ceramic nanoporous systems. Moreover, some specific characteristics of these materials, such as the consequences of the confinement of both gas and solid phases, are described. Likewise, the main production methods are briefly described. Finally, some of the potential applications of these materials are also discussed in this paper.Financial support from FPI Grant BES-2013-062852 (B. Notario) from the Spanish Ministry of Education is gratefully acknowledged. Financial assistance from the MINECO and FEDER Program (MAT 2012-34901) and the Junta of Castile and Leon (VA035U13) is gratefully acknowledge

La Burbuja Inmobiliaria de España: un análisis comparativo con el Mercado Inmobiliario chileno

El desarrollo de las empresas constructoras e inmobiliarias chilenas ha ido creciendo de manera acelerada, lo que implica una alta demanda de bienes inmuebles, tanto para inversión como adquisición de viviendas para las familias, por este motivo, el negocio inmobiliario lleva años con ventas al alza, y por consecuencia lógica, se han notado importantes aumentos en los precios de venta de las viviendas, incluso por sobre el IPC y rentas. Estas alzas vienen asociadas a la especulación de los últimos años por la reforma tributaria y la incorporación de la venta habitual de inmuebles al IVA, falta de suelo edificable, incremento en el número de créditos y aumento de duración de créditos hipotecarios. Este escenario, es similar al vivido por España, que se denominó “burbuja inmobiliaria” y que al explotar hizo caer la industria por la disminución de la demanda, impactando directamente a los precios, menor incentivo a inversionistas y desarrollo de proyectos, lo que sumado a la desaceleración del país significó una crisis de proporciones. Bajo esta idea general se busca desarrollar una investigación que analice los factores que influyeron en la formación de la burbuja inmobiliaria en España, de manera de poder realizar una comparación con el mercado chileno, que dé como resultado un análisis predictivo de los factores en que se debe tener especial hincapié en los próximos años de manera de evitar seguir el camino que lleve a una crisis inmobiliaria

Comportamiento agronómico de las hortalizas de fruto berenjena (Solanum melongena) y pepino (Cucumis sativus) con dos fertilizantes orgánicos en el centro experimental “La Playita” de la Universidad Técnica de Cotopaxi extensión La Maná. año 2014

The research was carried out in the Experimental "La Playita" of the Technical University of Cotopaxi, aimed to evaluate the agronomic performance of vegetables (cucumber and Eggplant) through the application of the Experimental Center of the Canton Beach organic fertilizers the Maná province of Cotopaxi. A complete block design applied to random (DBCA) with four treatments and five replications, each vegetable had five plants as experimental unit. Their results were: in cucumber the greatest number of fruits per plant was found in the vermicompost treatment with 1.40 g. and total fruits in the same treatment with 12,80 kg.; Vermicompost reported the highest values the variable length of fruit with 19.90 cm and diameter of fruit with 5.34 cm....La investigación se realizó en el Centro Experimental “La Playita” de la Universidad Técnica de Cotopaxi, tuvo como objetivo evaluar el comportamiento agronómico de hortalizas (pepino y berenjena) mediante la aplicación de fertilizantes orgánicos en el Centro Experimental la Playita del Cantón la Maná Provincia de Cotopaxi. Se aplicó un Diseño de Bloques Completos al Azar (DBCA) con cuatro tratamientos y cinco repeticiones, cada hortaliza tuvo cinco plantas como unidad experimental. Sus resultados fueron: En pepino el mayor número de frutos por planta se encontró en el tratamiento vermicompost con 1,40 g. y en el total de frutos en el mismo tratamiento con 12,80 kg...

Dielectric behavior of porous PMMA: From the micrometer to the nanometer scale

Producción CientíficaIn recent years, there has been a significant interest of the scientific community on nanocellular polymeric foams as a possible next generation of materials with a low dielectric constant for microelectronics applications In this work, the dielectric behavior of microcellular and nanocellular poly (methyl methacrylate) (PMMA) based foams has been characterized, both as a function of frequency and temperature, in order to analyze the effect of reducing the cell size to the nanoscale on the dielectric properties. Experimental results have shown clear differences in the dielectric behavior of the samples with cell sizes in the nanoscale as well as a sharp reduction of the dielectric constant when the porosity increases.Financial support from FPI grant BES-2013-062852 (B. Notario) from MINECO and FEDER program (MAT 2012-34901) MINECO, FEDER, UE (MAT2015-69234-R) and the Junta de Castile and Leon (VA035U13) are gratefully acknowledged