Analysis of the Cross Effects Found in Polymeric Cellular Materials Filled with Nanoadditives. Relationship between Dispersion and Foamability

El principal objetivo de este trabajo es estudiar el uso de nanopartículas en polímeros (tanto sólidos como espumados) y evaluar el nivel de dispersión de estas partículas dentro de la matriz polimérica. Para ello, la tesis de máster se enfocará en dos líneas de investigación: la primera está relacionada con la monitorización in-situ del proceso de exfoliación de un tipo de nanoarcilla (montmorillonita) en una matriz de polietileno durante el proceso de espumado usando agentes espumantes químicos. La segunda línea tiene por objetivo estudiar la dispersión de otro tipo de nanoarcillas (sepiolitas) en una matriz de poliestireno y su efectividad como agente nucleante. Estos resultados se compararán con los obtenidos para el talco, partícula más común usada como agente nucleante en la producción de espumas de poliestireno de baja densidad. Los materiales celulares han sido fabricados usando dos técnicas distintas: el espumado libre y el espumado por disolución de gas.Física de la Materia Condensada, Cristalografía y MineralogíaMáster en Nanociencia y Nanotecnología Molecula

Fabricación y caracterización de las propiedades físicas de polímeros nanocelulares: transición de la escala micro a la nano

Esta tesis se centra en la producción y posterior caracterización de espumas microcelulares y nanocelulares a partir de materiales basados en PMMA (poli(metil metacrilato)), mediante la técnica de espumado por disolución de gas usando CO2 como agente espumante. Debido a la novedad de este campo de investigación ha sido necesario optimizar el proceso de fabricación para obtener muestras con dimensiones y geometrías apropiadas (adaptables a los distintos protocolos de medida) y densidades relativas similares. Esto permitirá estudiar de forma sistemática la transición entre las espumas micro y nanocelulares, y analizar las potenciales aplicaciones que estas últimas pueden tener en la industria en un futuro cercano. Se ha encontrado una clara transición entre las espumas microcelulares y nanocelulares de PMMA en cuanto a las propiedades térmicas y mecánicas, y un comportamiento diferente en las propiedades dieléctricas y acústicas. Así mismo, se han encontrado nuevos efectos o comportamientos no esperados debidos al confinamiento de los elementos constituyentes de la espumas nanocelulares en el rango nanométrico.Departamento de Física de la Materia Condensada, Cristalografía y Mineralogí

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

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

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

Nanoporous PMMA foams with templated pore size obtained by localized in situ synthesis of nanoparticles and CO2 foaming

Producción CientíficaPolymer foams with controlled and templated pore size have been obtained for the first time by CO2 gas dissolution foaming from poly(methyl methacrylate) (PMMA) films. This kind of materials, with a variable porous structure, mimic some high-performance natural materials and could present significant interest in many applications. However, up to now their controlled fabrication has not been successfully achieved. Herein, we present a method to achieve a fine control in the production of such materials. Thermal in situ synthesis of ZnO nanoparticles from Zn(OAc)2 was proposed to obtain PMMA nanocomposites, in which the ZnO nanoparticles induce heterogeneous nucleation that leads to formation of pores with size below the micron, upon CO2 foaming. Starting from templated solid PMMA samples with well-differentiated regions, presenting or not ZnO nanoparticles, it was possible to obtain PMMA-based foams with well-defined areas of different pore sizes.Financial support from FPU grant FPU14/02050 (V. Bernardo) from the Spanish Ministry of Education is gratefully acknowledged. Financial assistance from MINECO, FEDER, UE (MAT2015-69234-R) and the Junta of Castile and Leon (VA011U16) are gratefully acknowledged. We also thank the organizers of the 2014 IIT Nanophysics Retreat for the fruitful discussions, which led to this work

How accurate are medical CT and micro-CT techniques compared to classical histology when addressing the growth of the internal rib parameters?

Rib internal anatomy and its cross-sectional morphology inform about important biomechanical or even evolutionary aspects. Classic histological studies require destructive techniques that are reprehensible depending on the case (e.g., fossils). In the last years, non-destructive CT-based methods are contributing to complementing previous knowledge without damaging the bone. Even though these methods have been proved to be useful to understand adult variation, we do not know whether these methods are useful to cover ontogenetic variation. This work compares classical histological methods with medical- and micro-CT to quantify the amount of mineral area at the rib midshaft (% Min. Ar.), a proxy for bone density. We compared cross-sections from an ontogenetic sample of 14 human first ribs ranging from perinates to adults using a) classical histology, b) HD (9–17 microns) and SD micro-CT (90 microns), and c) standard medical-CT (0.66 mm). We found that all the CT-based methods provide a larger % Min. Ar. compared to the histological techniques, but the HD micro-CT resolution is the only capable of producing results comparable to classical histology (p > 0.01), with the SD micro-CT and the medical-CT producing statistically larger results compared to classical histology (p < 0.01). In addition, it is important to state that the resolution of a standard medical-CT is not high enough to differentiate between mineral and non-mineral areas of the cross-sections for perinates and infants. These results could have important implications to avoid (when necessary) destructive techniques that are not appropriate in the case of highly valuable specimens such as fossils.Peer reviewe