Search results for " Materiales"
showing 10 items of 104 documents
Effective antimicrobial materials based on low-density polyethylene (LDPE) with zinc oxide (ZnO) nanoparticles
2019
[EN] Effective antimicrobial polymeric nanocomposites were prepared with low density polyethylene (LDPE) and zinc oxide nanoparticles by melt compounding. These nanoparticles (~17 nm) obtained by the sol¿gel method, were used both as-synthesized and modified organically with oleic acid (Mod-ZnO). Young¿s modulus increased ~15 and 18% for LDPE/ZnO and LDPE/Mod-ZnO, respectively, compared to neat LDPE. When these composites were irradiated with white light, they showed an increase with nanoparticle incorporation, and the antimicrobial properties against E. coli were ~96¿99%. The release of the Zn cations was related to the antimicrobial properties. These nanocomposites are attractive for use …
Nanorings and rods interconnected by self-assembly mimicking an artificial network of neurons
2013
[EN] Molecular electronics based on structures ordered as neural networks emerges as the next evolutionary milestone in the construction of nanodevices with unprecedented applications. However, the straightforward formation of geometrically defined and interconnected nanostructures is crucial for the production of electronic circuitry nanoequivalents. Here we report on the molecularly fine-tuned self-assembly of tetrakis-Schiff base compounds into nanosized rings interconnected by unusually large nanorods providing a set of connections that mimic a biological network of neurons. The networks are produced through self-assembly resulting from the molecular conformation and noncovalent intermo…
Defect spectroscopy of single ZnO microwires
2014
The point defects of single ZnO microwires grown by carbothermal reduction were studied by microphotoluminescence, photoresistance excitation spectra, and resistance as a function of the temperature. We found the deep level defect density profile along the microwire showing that the concentration of defects decreases from the base to the tip of the microwires and this effect correlates with a band gap narrowing. The results show a characteristic deep defect levels inside the gap at 0.88 eV from the top of the VB. The resistance as a function of the temperature shows defect levels next to the bottom of the CB at 110 meV and a mean defect concentration of 4 1018 cm3 . This combination of tech…
Shear-aligned block copolymer monolayers as seeds to control the orientational order in cylinder-forming block copolymer thin films
2016
We study the dynamics of coarsening of a cylinder-forming block copolymer thin film deposited on a prepatterned substrate made of a well-ordered block copolymer monolayer. During thermal annealing the shear-aligned bottom layer drives extinction of the disclinations and promotes a strong orientational correlation, disturbed only by dislocations and undulations along the cylinders of the minority phase. The thin film bilayer system remains stable during annealing, in agreement with self-consistent field theory results that indicate that although the thickness of a stack of two monolayers is not at the optimum thickness condition, it is very close to equilibrium. Phase field simulations indic…
Densely packed semiflexible macromolecules in a rigid spherical capsule
2018
The ordering of semiflexible polymers with persistence length lp and contour length L confined in a sphere of radius R is studied by molecular dynamics simulations of a coarse-grained model. Monomer densities are chosen where the corresponding bulk lyotropic solution or melt is a well-ordered nematic, and purely repulsive walls of the rigid confining sphere are considered. It is found that polymers close to the walls are bent according to the curvature of the confining spheres with all their monomers in a few layers parallel to the sphere surface, whereas the remaining macromolecules closer to the sphere center have one chain end and their center of mass far from the surface. The latter cha…
Microstructure and mechanical properties of plasma spraying coatings from YSZ feedstocks comprising nano-and submicron-sized particles
2015
Atmospheric plasma spraying (APS) is an attractive technique to obtain nanostructured coatings due to its versatility, simplicity and relatively low cost. However, nanoparticles cannot be fed into the plasma using conventional feeding systems, due to their low mass and poor flowability, and must be adequately reconstituted into sprayable micrometric agglomerates. In this work, nanostructured and submicron/nanostiuctured powders of yttria-stabilised zirconia (YSZ) were deposited using APS, with a view to obtaining high-performance thermal bather coatings (IBC). All powders were reconstituted by spray-drying from different solid loading suspensions, followed by a thermal treatment of the spra…
Polylactide-based self-reinforced composites biodegradation: Individual and combined influence of temperature, water and compost
2018
[EN] Self-reinforced polymer composites (SRCs) are proposed as a suitable alternative for composite development, based in the combination of a polymeric matrix and a polymeric fibre made of the same polymer. SRCs based in polylactide (PLA) could be fully biodegradable and their valorisation routes could presumably be assimilated to those for neat PEA. In this sense, the aim of this study was to develop new self-reinforced PLA-based composites and ascertain their biodegradability. For this purpose, PLA-based SRCs were obtained through a thermo-compression procedure and their biodegradability corroborated under standard conditions (ISO 20200). Moreover, a deep study of the effect of the diffe…
Comparative characterization of a novel cad-cam polymer-infiltrated-ceramic-network.
2015
Background The field of dental ceramics for CAD-CAM is enriched with a new innovative material composition having a porous three-dimensional structure of feldspathic ceramic infiltrated with acrylic resins.The aim of this study is to determine the mechanical properties of Polymer-Infiltrated-Ceramic-Network (PICN) and compare its performance with other ceramics and a nano-ceramic resin available for CAD-CAM systems. Material and Methods In this study a total of five different materials for CAD-CAM were investigated. A polymer-infiltrated ceramic (Vita Enamic), a nano-ceramic resin (Lava Ultimate), a feldspathic ceramic (Mark II), a lithium disilicate ceramic (IPS-e max CAD) and finally a Le…
Cobalt ferrite nanoparticles under high pressure
2015
We report by the first time a high pressure X-ray diffraction and Raman spectroscopy study of cobalt ferrite (CoFe2O4) nanoparticles carried out at room temperature up to 17 GPa. In contrast with previous studies of nanoparticles, which proposed the transition pressure to be reduced from 20–27 GPa to 7.5–12.5 GPa (depending on particle size), we found that cobalt ferrite nanoparticles remain in the spinel structure up to the highest pressure covered by our experiments. In addition, we report the pressure dependence of the unit-cell parameter and Raman modes of the studied sample. We found that under quasi-hydrostatic conditions, the bulk modulus of the nanoparticles (B0 = 204 GPa) is consid…
Impact of hydrothermal ageing on the thermal stability, morphology and viscoelastic performance of PLA/sisal biocomposites
2016
The influence of the combined exposure to water and temperature on the behaviour of polylactide/sisal biocomposites coupled with maleic acid anhydride was assessed through accelerated hydrothermal ageing. The biocomposites were immersed in water at temperatures from 65 to 85 °C, between the glass transition and cold crystallisation of the PLA matrix. The results showed that the most influent factor for water absorption was the percentage of fibres, followed by the presence of coupling agent, whereas the effect of the temperature was not significant. Deep assessment was devoted to biocomposites subjected to hydrothermal ageing at 85 °C, since it represents the extreme degrading condition. Th…