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Lizundia E.,University of the Basque Country | Vilas J.L.,University of the Basque Country | Vilas J.L.,Basque Center for Materials | Sangroniz A.,University of the Basque Country | Etxeberria A.,University of the Basque Country
European Polymer Journal | Year: 2017

Herein we attempt to provide a deeper understanding on the influence of metal oxide nanoparticle incorporation on the gas transport properties of resulting polymer-based nanocomposites. Polylactide has been used as a model biodegradable material to develop nanocomposites containing 1 v/v% of TiO2, SiO2, Fe2O3 and Al2O3 spherical particles. These nanoparticles were characterized by transmission electron microscopy (TEM), X-ray and ζ-potential measurements. Thermal properties of nanocomposites were analyzed by differential scanning calorimetry (DSC), while scanning electron microscopy (SEM) has been used to correlate nanoparticle dispersion with both light and gas barrier properties. UV–Vis spectroscopy indicates a good UV-shielding performance of developed films. Water vapour transmission rate and oxygen permeability of nanocomposites were further determined and obtained results have been correlated to the effect of interactions between the incorporated nanoparticles and water/oxygen molecules. Taking into account that only 1% of nanoparticles have been added, noticeable improvement of the barrier character of polylactide to water vapour, up to 18%, and wet oxygen, up to 9%, have been observed. Finally, Maxwell, Bruggeman, Böttcher and Higuchi models have been applied for our two-phase mixed matrix membranes to predict the permeability of dry oxygen. Overall, the experimental findings here shown provide better understanding towards the design of membrane devices based on biodegradable materials with tailored light and gas permeability for specific industrial applications. © 2017 Elsevier Ltd

Goncalves R.,University of Minho | Martins P.,University of Minho | Correia D.M.,University of Minho | Sencadas V.,University of Minho | And 5 more authors.
RSC Advances | Year: 2015

Magnetoelectric microspheres based on piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive CoFe2O4 (CFO), a novel morphology for polymer-based ME materials, have been developed by an electrospray process. The CFO nanoparticle content in the (3-7 μm diameter) microspheres reaches values up to 27 wt%, despite their concentration in the starting solution reaching values up to 70 wt%. Additionally, the inclusion of magnetostrictive nanoparticles into the polymer spheres has no relevant effect on the piezoelectric β-phase content (≈60%), crystallinity (40%) and the onset degradation temperature (460-465°C) of the polymer matrix. The multiferroic microspheres show a maximum piezoelectric response d33 ≈ 30 pC N-1, leading to a magnetoelectric response of Δd33 ≈ 5 pC N-1 obtained when a 220 mT DC magnetic field was applied. It is also shown that the interface between CFO nanoparticles and PVDF (from 0 to 55%) has a strong influence on the ME response of the microspheres. The simplicity and the scalability of the processing method suggest a large application potential of this novel magnetoelectric geometry in areas such as tissue engineering, sensors and actuators. © The Royal Society of Chemistry 2015.

Garcia-Huete N.,Basque Center for Materials | Laza J.M.,University of the Basque Country | Cuevas J.M.,Gaiker Technology Center | Vilas J.L.,Basque Center for Materials | And 2 more authors.
Radiation Physics and Chemistry | Year: 2014

A gamma radiation process for modification of commercial polymers is a widely applied technique to promote new physical, chemical and mechanical properties. Gamma irradiation originates free radicals able to induce chain scission or recombination of radicals, which induces annihilation, branching or crosslinking processes. The aim of this work is to research the structural, thermal and mechanical changes induced on a commercial polycyclooctene (PCO) when it is irradiated with a gamma source of 60Co at different doses (25-200kGy). After gamma irradiation, gel content was determined by Soxhlet extraction in cyclohexane. Furthermore, thermal properties were evaluated before and after Soxhlet extraction by means of Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), as well as mechanical properties were measured by Dynamic Mechanical Thermal Analysis (DMTA). The results showed the variations of the properties depending on the irradiation dose. Finally, a first approach to evaluate qualitatively the shape memory behaviour of all irradiated PCO samples was performed by a visually monitoring shape recovery process. © 2014 Elsevier Ltd.

Iturrospe A.,University of the Basque Country | San Felices L.,University of the Basque Country | Reinoso S.,University of the Basque Country | Artetxe B.,University of the Basque Country | And 4 more authors.
Crystal Growth and Design | Year: 2014

Hydrothermal reaction of the Keggin-type [-GeW11O 39]8- anion with copper(II) complexes of the tetradentate N-donor ligands N,N′-dimethyl-N,N′-bis-(pyridine-2-ylmethyl)-1,2- diaminoethane (bpmen) or N,N′-dimethyl-N,N′-bis-(pyridine-2- ylmethyl)-1,3-diaminopropane (bpmpn) results in three new hybrid compounds [Cu(bpmen)(H2O)][GeW12O40{Cu(bpmen)}]·3. 5H2O (1), [GeW12O40{Cu(bpmpn)(H 2O)}2]·3H2O (2), and [Cu(bpmpn)(H 2O)][GeW12O40{Cu(bpmpn)}]·8H 2O (3). All compounds have been characterized by elemental analyses and infrared spectroscopy, and their structures have been established by single-crystal X-ray diffraction. Both 1 and 3 contain monodecorated polyanions and additional complex cations, but their layered structures show noticeable differences. For 1, the polyanions are arranged in rows whose stacking generates intralamellar cavities where complex cations and lattice water molecules are hosted, whereas double-layers of hybrid anions pillared by the cations occupying the interlamellar space are observed for 3. In the case of 2, the packing of trans-didecorated clusters generates honeycomb-like metalorganic layers and perpendicular hexagonal channels where Keggin moieties are nested. A combination of thermogravimetric and variable temperature powder X-ray diffraction analyses show that dehydration of 1 and 2 results in thermally stable, crystalline phases. Dehydrations are fully reversible upon exposure to air and proceed via single-crystal to single-crystal transformations implying rupture/formation processes in the copper(II) bonding and consequent geometrical and conformational modifications in the complexes. Transformations have been followed by single-crystal X-ray diffraction, allowing for the structures of the anhydrous phases [GeW12O40{Cu(bpmen)}2] (1a) and [GeW12O40{Cu(bpmpn)}2] (2a) to be determined. Dehydration of 1 into 1a with consequent formation of neutral, didecorated clusters does not result in the collapse of the intralamellar cavities but rather in an open-framework structure with slit-shaped micropores. Structural variations between 1 and 2 and their corresponding anhydrous phases are reflected in the electron paramagnetic resonance spectra. © 2014 American Chemical Society.

Legarra E.,Basque Center for Materials | Apinaniz E.,University of the Basque Country | Plazaola F.,University of the Basque Country
Intermetallics | Year: 2016

The influence of the different crystal structures and the variation of the lattice parameter on the evolution of the magnetism in the order-disorder transition produced by crushing and mechanical milling in the intermetallic Fe75Al25-xSix alloys (x = 7.5, 12.5, 17.5, 25) has been systematically studied by means of XRD measurements, Mössbauer spectroscopy and magnetic measurements. The results indicate that with the addition of Si to binary Fe75Al25 alloy the mechanical deformation needed to disorder the alloys increases. At the same time the variation of the lattice parameter due to the disorder is reduced as Si is added. The magnetic measurements indicate that there is a complex behaviour in ternary alloys with an opposite influence of Si and Al during the order-disorder transition. However, when the transition is fulfilled there is a linear relationship between structural and magnetic parameters. © 2015 Elsevier Ltd.

Lizundia E.,University of the Basque Country | Vilas J.L.,Basque Center for Materials | Leon L.M.,University of the Basque Country | Leon L.M.,Basque Center for Materials
Carbohydrate Polymers | Year: 2015

In this work, crystallization, structural relaxation and thermal degradation kinetics of neat Poly(l-lactide) (PLLA) and its nanocomposites with cellulose nanocrystals (CNC) and CNC-grafted-PLLA (CNC-g-PLLA) have been studied. Although crystallinity degree of nanocomposites remains similar to that of neat homopolymer, results reveal an increase on the crystallization rate by 1.7-5 times boosted by CNC, which act as nucleating agents during the crystallization process. In addition, structural relaxation kinetics of PLLA chains has been drastically reduced by 53% and 27% with the addition of neat and grafted CNC, respectively. The thermal degradation activation energy (E) has been determined from thermogravimetric analysis in the light of Kissinger's and Ozawa-Flynn-Wall theoretical models. Results reveal a reduction on the thermal stability when in presence of CNC-g-PLLA, while raw CNC slightly increases the thermal stability of PLLA. Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy results confirm that the presence of residual catalyst in CNC-g-PLLA plays a pivotal role in the thermal degradation behavior of nanocomposites. © 2015 Elsevier Ltd. All rights reserved.

Legarra E.,Basque Center for Materials | Apinaniz E.,University of the Basque Country | Plazaola F.,University of the Basque Country
Journal of Alloys and Compounds | Year: 2016

The aim of this work is to study the influence of the coexistence of different ordered structures on the evolution of the magnetism in the order-disorder transition produced by crushing and mechanical milling in the intermetallic Fe70Al30-xSix alloys. First, XRD measurements show that the three ordered samples have both D03 and B2 structures simultaneously and that the disordering process takes place in two stages. In the first one the D03 structure starts to disorder and in the second one, once the D03 structure has almost disappeared, the B2 starts to disorder. Second, Mössbauer spectroscopy and magnetic measurements show that there is an enhancement of the magnetic properties related to the structure change and to the increase of the lattice parameter in the order-disorder transition. The change of the magnetic behaviour is linked to the disordering of B2 structure in these alloys. © 2016 Elsevier B.V.

Garcia-Huete N.,Basque Center for Materials | Laza J.M.,University of the Basque Country | Cuevas J.M.,Gaiker Technology Center | Gonzalo B.,Gaiker Technology Center | And 2 more authors.
Journal of Polymer Research | Year: 2014

Self-repair properties based on shape-memory features of covalently crosslinked semi-crystal line polyalkenamers were demonstrated by thermal-activated recovery of performed surface marks (indented holes and scratches). Shape memory polymers were prepared by mixing a commercial polycyclooctene (PCO) with different percentages of peroxide, and then these mixtures were processed by compression moulding to obtain crosslinked sheets. With the aid of a hardness test pencil, holes and scratches in the surface of the materials were realized with different known forces (5, 10 and 15 N). The disappearance of surface defects was evaluated using both optical and contact surface profilometry, as well as optical microscopy under heating processes. This technique allowed evaluating shape recovery ratios of edgewise holes in PCO samples. In parallel, the analysis of maximum depth of indentations with temperature for edgewise samples by optical microscopy allows evaluating shape recovery. As a complementary tool for analysing thermal shaperecovery and surface resistance to indentation, thermal properties and hardness were investigated by DSC and Shore durometer test, respectively. © Springer Science+Business Media Dordrecht 2014.

PubMed | Basque Center for Materials
Type: Journal Article | Journal: Nanotechnology | Year: 2016

Permalloy disc structures in magnetic vortex state constitute a promising new type of magnetic nanoparticles for biomedical applications. They present high saturation magnetisation and lack of remanence, which ease the remote manipulation of the particles by magnetic fields and avoid the problem of agglomeration, respectively. Importantly, they are also endowed with the capability of low-frequency magneto-mechanical actuation. This effect has already been shown to produce cancer cell destruction using functionalized discs, about 1 m in diameter, attached to the cell membrane. Here, Permalloy nanodiscs down to 60 nm in diameter are obtained by hole-mask colloidal lithography, which is proved to be a cost-effective method for the uniform patterning of large substrate areas, with a high production yield of nanostructures. The characterisation of the magnetic behaviour of the nanodiscs, complemented with micromagnetic simulations, confirms that they present a very well defined magnetic vortex configuration, unprecedented, to our knowledge, for nanostructures of this size prepared by a high-yield method. The successful detachment of the gold-covered nanodiscs from the substrate is also demonstrated by the use of sacrificial layers.

PubMed | Basque Center for Materials and University of the Basque Country
Type: Journal Article | Journal: Acta crystallographica. Section E, Crystallographic communications | Year: 2016

Single crystals of the title compound, potassium hexa-phosphito-penta-ferrate(II,III) hemihydrate, K0.75[Fe(II) 3.75Fe(III) 1.25(HPO3)6]0.5H2O, were grown under mild hydro-thermal conditions. The crystal structure is isotypic with Li1.43[Fe(II) 4.43Fe(III) 0.57(HPO3)6]1.5H2O and (NH4)2[Fe(II) 5(HPO3)6] and exhibits a [Fe(II) 3.75Fe(III) 1.25(HPO3)6](0.75-) open framework with disordered K(+) (occupancy 3/4) as counter-cations. The anionic framework is based on (001) sheets of two [FeO6] octa-hedra (one with point group symmetry 3.. and one with point group symmetry .2.) linked along [001] through [HPO3](2-) oxoanions. Each sheet is constructed from 12-membered rings of edge-sharing [FeO6] octa-hedra, giving rise to channels with a radius of ca 3.1 where the K(+) cations and likewise disordered water mol-ecules (occupancy 1/4) are located. OO contacts between the water mol-ecule and framework O atoms of 2.864(5) indicate hydrogen-bonding inter-actions of medium strength. The infrared spectrum of the compound shows vibrational bands typical for phosphite and water groups. The Mssbauer spectrum is in accordance with the presence of Fe(II) and Fe(III) ions.

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