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Moussaif N.,Technological Institute of Aragon ITA | Irusta S.,University of Zaragoza | Irusta S.,CIBER ISCIII | Yague C.,University of Zaragoza | And 6 more authors.
Polymer | Year: 2010

Biodegradable nanocomposites consisting of poly(e{open}-caprolactone) (PCL) reinforced by PEGylated silica (polyethylene-glycol/SiO2) nanoparticles were prepared by a melt-extrusion process. The PEGylated silica nanoparticles were prepared in a facile, one-pot synthesis process. Transmission electron microscopy (TEM) observations of the PEGylated silica nanoparticles inside the PCL matrix indicated that a homogeneous dispersion had been achieved. As a result, the storage modulus (E') in the rubbery plateau increased significantly with the filler contents at all temperatures studied, at values approximately 45% higher than the neat PCL, at a loading level of only 4wt.%. In comparison, in the absence of polyethylene-glycol (PEG) the silica nanoparticles formed aggregates inside the PCL matrix, and the reinforcement was negligible. The results from X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) analyses identified the location of the PEG at the PCL/silica interface. © 2010 Elsevier Ltd.


Castrillon M.,Technological Institute of Aragon ITA | Mayoral A.,University of Zaragoza | Magen C.,University of Zaragoza | Meier J.G.,Technological Institute of Aragon ITA | And 5 more authors.
Nanotechnology | Year: 2012

Ultra-small magnetic nanoparticles consisting of NiCo and FeNi alloys enclosed within graphitic shells (NiCo/G and FeNi/G) have been synthesized. The particles, which retained the face centered cubic (fcc) symmetry of the original bulk metals, together with the graphitic coating were characterized by means of aberration corrected scanning transmission electron microscopy (STEM), obtaining mean particle sizes of 2.6nm and 6.2nm for NiCo/G and FeNi/G, respectively. Due to the enhancement of the thermal stability by the graphite shell, the graphite coated FeNi and NiCo were stable under oxygen atmosphere up to 170°C. The effectiveness of the graphite shell was confirmed when unprotected bimetallic FeNi and NiCo were prepared and chemical characterization revealed that more than 60at.% of the samples was oxygen due to the massive oxidation of the bimetallic nanoparticles. © 2012 IOP Publishing Ltd.


Castrillon M.,Technological Institute of Aragon ITA | Mayoral A.,University of Zaragoza | Urtizberea A.,University of Zaragoza | Marquina C.,University of Zaragoza | And 5 more authors.
Nanotechnology | Year: 2013

FeCo-alloy graphite-coated nanoparticles with mean particle diameter under 8 nm have been synthesized following a CVD carbon-deficient method. The superior magnetic properties of FeCo-alloy nanoparticles makes them good candidates to be used as magnetic filler in magneto-polymer composites. Thanks to the protective effect of the graphite shell, FeCo nanoparticles are stable under oxygen atmosphere up to 200°C. The as-prepared nanoparticles presented a highly long range chemically ordered core being ferromagnetic at room temperature with a saturation magnetization at room temperature close to the bulk value. After annealing at 750 K the saturation magnetization and the coercive field increase. To investigate the processes involved in the thermal treatment, the temperature dependence of the magnetization and the particle composition, size and structure have been characterized before and after annealing. Besides powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), a detailed study by means of advanced transmission electron microscopy (TEM) techniques has been carried out. In particular, aberration corrected scanning transmission electron microscopy (STEM), has shown that nanoparticles became faceted after the thermal treatment, as a mechanism to reach the thermodynamic equilibrium within the metastable phase. This outstanding feature, not previously reported, leads to an increase of the shape anisotropy, which in turn might be the origin of the observed increase of the coercive field after annealing. © 2013 IOP Publishing Ltd.


Moussaif N.,Technological Institute of Aragon ITA | Crespo C.,Technological Institute of Aragon ITA | Meier J.G.,Technological Institute of Aragon ITA | Jimenez M.A.,Technological Institute of Aragon ITA
Polymer (United Kingdom) | Year: 2012

Biodegradable nanocomposites based on poly(ε-caprolactone) (PCL) reinforced by mesoporous silicate (MCM) were prepared by a melt-extrusion process using a second nanoclay, i.e. modified organophilic silicate layers as compatibilizer. The compatibilizing role of the nanoclay was studied with respect to the morphological, melt-rheological and dynamic mechanical properties of these nanocomposites. Transmission electron microscopy showed that a homogeneous dispersion of MCM had been achieved with addition of the nanoclay (0.5 wt.%) to the PCL/MCM composite. Oscillatory frequency sweep measurements showed that addition of about 3.0 wt.% MCM, in the presence of silicate layers (0.5 wt.%), led to a solid-like response where a percolated network structure is formed. As a result, the Elastic modulus (E), in the rubbery plateau, increased significantly with the filler contents at all temperatures studied, having, at a loading level of only 4 wt.%, values approximately 50% higher than the neat PCL. This reinforcement is probably due to a synergistic effect that arises from the combination of the modified layered clays and the mesoporous silicate particles. In comparison, in the absence of silicate layers, the mesoporous silicate aggregates inside the PCL matrix, and the reinforcement was negligible. © 2012 Published by Elsevier Ltd.


PubMed | Technological Institute of Aragon ITA
Type: Journal Article | Journal: Nanotechnology | Year: 2012

Ultra-small magnetic nanoparticles consisting of NiCo and FeNi alloys enclosed within graphitic shells (NiCo/G and FeNi/G) have been synthesized. The particles, which retained the face centered cubic (fcc) symmetry of the original bulk metals, together with the graphitic coating were characterized by means of aberration corrected scanning transmission electron microscopy (STEM), obtaining mean particle sizes of 2.6nm and 6.2nm for NiCo/G and FeNi/G, respectively. Due to the enhancement of the thermal stability by the graphite shell, the graphite coated FeNi and NiCo were stable under oxygen atmosphere up to 170C. The effectiveness of the graphite shell was confirmed when unprotected bimetallic FeNi and NiCo were prepared and chemical characterization revealed that more than 60at.% of the samples was oxygen due to the massive oxidation of the bimetallic nanoparticles.


PubMed | Technological Institute of Aragon ITA
Type: Journal Article | Journal: Nanotechnology | Year: 2013

FeCo-alloy graphite-coated nanoparticles with mean particle diameter under 8 nm have been synthesized following a CVD carbon-deficient method. The superior magnetic properties of FeCo-alloy nanoparticles makes them good candidates to be used as magnetic filler in magneto-polymer composites. Thanks to the protective effect of the graphite shell, FeCo nanoparticles are stable under oxygen atmosphere up to 200 C. The as-prepared nanoparticles presented a highly long range chemically ordered core being ferromagnetic at room temperature with a saturation magnetization at room temperature close to the bulk value. After annealing at 750 K the saturation magnetization and the coercive field increase. To investigate the processes involved in the thermal treatment, the temperature dependence of the magnetization and the particle composition, size and structure have been characterized before and after annealing. Besides powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), a detailed study by means of advanced transmission electron microscopy (TEM) techniques has been carried out. In particular, aberration corrected scanning transmission electron microscopy (STEM), has shown that nanoparticles became faceted after the thermal treatment, as a mechanism to reach the thermodynamic equilibrium within the metastable phase. This outstanding feature, not previously reported, leads to an increase of the shape anisotropy, which in turn might be the origin of the observed increase of the coercive field after annealing.

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