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Vila Nova de Famalicão, Portugal

Lopes A.C.,University of Minho | Goncalves R.,University of Minho | Costa C.M.,nter for Nanotechnology and Smart Materials | Fonseca A.M.,University of Minho | And 3 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2012

Polymer based composites of -PVDF doped with different NaY zeolite (Na53Al53Si139O384 content were investigated. A good dispersion of NaY zeolite within the polymer matrix is achieved. The introduction of NaY nanoparticles enhance the storage modulus and the dielectric constant at room temperature. The dielectric constant at room temperature increases up to the value of 500 for the 32 wt% composite, at 1 kHz. The increase of the dielectric constant is mainly attributed to interfacial polarization effects. For increasing zeolite content, the nanocomposite conductivity shows two conducting regimes separted by the so called breaking voltage, which is associated to an intrazeolite charge transport. Thermogravimetric results show that the introduction of zeolites affects the thermal degradation of the polymer for low zeolite contents and also indicate the presence of water that also plays an important role in the electrical response of the materials. Copyright © 2012 American Scientific Publishers.

Magalhaes R.,University of Minho | Duraes N.,nter for Nanotechnology and Smart Materials | Silva M.,University of Minho | Silva J.,University of Minho | And 6 more authors.
Soft Materials | Year: 2011

Electroactive β-poly(vinylidene fluoride) (PVDF) membranes were obtained by isothermal crystallization from the solution. Different morphologies and microstructures were obtained by crystallizing at different temperatures. The mechanism and kinetics of solvent evaporation from the polymeric solution were investigated using isothermal thermogravimetric analysis. The kinetic parameters and the activation energy were also calculated. The solvent evaporation is ruled by two steps, related with a metastable- unstable-metastable transition in the solution phase diagram. Scanning electron microscopy revealed the porous structure and the variations of the morphology with the variation of the isothermal evaporation temperature. Finally, the infrared spectroscopy measurements confirm that the polymer crystallizes in the electroactive-phase of PVDF. © 2010 Taylor & Francis Group, LLC.

Costa C.M.,University of Minho | Costa C.M.,nter for Nanotechnology and Smart Materials | Firmino Mendes S.,University of Minho | Sencadas V.,University of Minho | And 6 more authors.
Journal of Non-Crystalline Solids | Year: 2010

In this work, poly(vinilidene fluoride)/Pb(Zr0.53Ti 0.47)O3,([PVDF]1 - x/[PZT]x) composites of ceramic volume fractions x and (0-3) type connectivity were prepared in the form of thin films. PZT powders with average grain size of 0.84, 1.86 and 2.35 μm in different volume fraction of PZT (10, 20, 30 and 40%) were mixed with the polymer matrix. The PVDF crystalline phase was the nonpolar α-phase and the polar β-phase. Dielectric measurements were performed and the study revealed that the dielectric constant of the materials strongly increases with increasing PZT particle content. The quasi-static and dynamic mechanical properties of the composites are also strongly dependent on the PZT volume fraction. The grain size of the ceramic particles and the PVDF crystalline phase do not affect significantly neither dielectric nor the mechanical response. Scanning electron microscopy, Fourier transformed infrared spectroscopy and differential scanning calorimetry measurements were performed in order to study the distribution of particles within the polymer matrix, the influence of these particles at a molecular level and the variations induced in the melting transition and in the degree of crystallinity of the composites, respectively. © 2010 Elsevier B.V.

Ribeiro C.,University of Minho | Sencadas V.,University of Minho | Costa C.M.,University of Minho | Costa C.M.,nter for Nanotechnology and Smart Materials | And 4 more authors.
Science and Technology of Advanced Materials | Year: 2011

Biodegradable poly(L-lactic acid) (PLLA) microfibers were prepared by electrospinning by varying the applied potential, solution flow rate and collector conditions. PLLA fibers with smoothly oriented and random morphologies were obtained and characterized by scanning electron microscopy. The optimum fiber orientation was obtained at 1000 rpm using a 20.3 cm diameter collecting drum, while for higher and lower drum rotation speeds, the rapid random motion of the jets resulted in a random fiber distribution. The deformation of the jet with rapid solidification during electrospinning often results in a metastable phase. PLLA electrospun fibers are amorphous but contain numerous crystal nuclei that rapidly grow when the sample is heated to 70-140 °C. In this way, the degree of crystallinity of the fibers can be tailored between 0 and 50% by annealing. Infrared transmission spectra revealed that the processing conditions do not affect the PLLA samples at the molecular level and that the crystallinity of the samples is related to the presence of α-crystals. © 2011 National Institute for Materials Science.

Martins P.,University of Minho | Costa C.M.,nter for Nanotechnology and Smart Materials | Lanceros-Mendez S.,University of Minho
Applied Physics A: Materials Science and Processing | Year: 2011

Multiferroic and magnetoelectric materials show enormous potential for technological developments. Multiferroic composites are more attractive for applications due to their enhanced properties with respect to single-phase multiferroic materials. In this paper we report on the nucleation of the electroactive β-phase of poly(vinylidene fluoride), PVDF, by the addition of CoFe2O4 and NiFe2O4 nanoparticles in order to prepare poly(vinylidene fluoride)/ferrite nanocomposite for multiferroic and magnetoelectric applications,. The dispersed ferrite nanofiller particles strongly enhance the nucleation of the β-phase of the polymer matrix. In this way, magnetoelectric polymer nanocomposites can be processed avoiding the usual α- to β-phase transformation by stretching of the polymer matrix. © 2010 Springer-Verlag.

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