Vila Nova de Famalicão, Portugal
Vila Nova de Famalicão, Portugal

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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.


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.


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.


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.


Gomes J.,nter for Nanotechnology and Smart Materials | Nunes J.S.,University of Minho | Sencadas V.,University of Minho | Lanceros-Mendez S.,University of Minho
Smart Materials and Structures | Year: 2010

The ferroelectric switching behaviour and piezoelectric response of poly(vinylidene fluoride) (PVDF) prepared by drawing at stretching ratios from 1 to 5 and temperatures from 80 to 140 °C has been studied. Stretching ratio and temperature deeply influence the α (non-ferroelectric) to β (ferroelectric) phase transformation. The variations in the phase content are accompanied by changes in the degree of crystallinity and the microstructure, all of them influencing the macroscopic piezoelectric and ferroelectric response of the material. This work shows how the piezo-and ferroelectric behaviour of PVDF depends on the aforementioned parameters and, in particular, on the crystalline β-phase content. Coercive electric field, remnant polarization and saturation polarization increase with increasing ferroelectric β-phase content in the sample. In a similar way, samples with higher β-phase content show higher d33 piezoelectric coefficients. © 2010 IOP Publishing Ltd.


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.


Costa C.M.,nter for Nanotechnology and Smart Materials | Gomes J.,nter for Nanotechnology and Smart Materials | Nunes J.S.,University of Minho | Sencadas V.,University of Minho | Lanceros-Mendez S.,University of Minho
International Journal of Materials and Product Technology | Year: 2010

The phase transformation from α to β Poly(vinylidene fluoride) (PVDF) through an stretching process at a given temperature and stretching ratio allows controlling the phase content and therefore the electroactive properties of the polymer. Inhomogeneous stretching allows tailoring these properties along a given sample and to obtain graded electroactive and optical properties within the same plate of material from the micro to the macroscopic scale, increasing the potential of PVDF for advance applications. Copyright © 2010 Inderscience Enterprises Ltd.


Trindade A.J.,University of Aveiro | Santos M.G.,University of Aveiro | Gomes J.,nter for Nanotechnology and Smart Materials | Pereira L.,nter for Nanotechnology and Smart Materials
Materials Research Society Symposium Proceedings | Year: 2011

This work shows the relationship between the morphology (studied by AFM) of an active bulk-heterojunction (BHJ) layer composed by MEH-PPV (poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) and the respective photovoltaic figures of merit. It is observed that the most relevant parameter (influencing the efficiency) is the fill-factor (FF), as both the open circuit voltage and short circuit current are not significantly affected by the microscopic morphology. Different local conformation of the active films can change the FF from near 25% to more than 65%, having a strong impact in the efficiency. These results were modulated by an equivalent circuit. Serial and parallel resistances were related with the physical behavior of the organic cells. These were observed to have a direct relationship with the achieved morphology. © 2011 Materials Research Society.


Vilela C.,University of Aveiro | Santos S.A.O.,University of Aveiro | Coelho D.,University of Aveiro | Coelho D.,nter for Nanotechnology and Smart Materials | And 4 more authors.
Industrial Crops and Products | Year: 2014

The chemical composition of the lipophilic and phenolic extractives of the leaves, stems and roots of the salt marsh plant Halimione portulacoides from the Aveiro Lagoon was thoroughly investigated by gas chromatography-mass spectrometry (GC-MS) and ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS), respectively. The lipophilic fraction of leaves and stems is mainly composed of long chain aliphatic acids and alcohols (both in the C16-C30 range) and smaller amounts of sterols, such as schottenol, β-sitosterol and β-sitostanol. The major component of roots extract is a triterpenic ketone, hop-17(21)-en-3-one, accounting for 2.8gkg-1 of dry material. Furthermore, thirteen phenolic compounds were firstly reported as constituents of this halophytic shrub. Among the studied plant tissues, leaves are the richest in phenolic compounds with 4.6gkg-1 of dry material, most of which correspond to sulfated flavonoids (3.1gkg-1 of dry material), particularly derivatives of isorhamnetin-sulfate. © 2013 Elsevier B.V.


Santos J.M.R.C.A.,nter for Nanotechnology and Smart Materials | Sampaio A.R.,nter for Nanotechnology and Smart Materials | Branquinho J.,nter for Nanotechnology and Smart Materials
Journal of Renewable Materials | Year: 2016

Cellulose-based materials are one of the most widely used materials provided by nature to mankind. In particular, cotton fi bers have been used for millennia to produce clothing items. This wide usage stems from the inherent properties of cotton fabrics such as hydrophilicity and permeability to water vapor. However, increasingly sophisticated uses for cotton-based clothing (e.g., technical textiles) demand specifi c properties such as hydrophobicity and oleophobicity for repellent functions. The current surface treatments used to attain these functionalities are based on thermally initiated polymerization reactions, using water-based formulations. Thus, the current technologies are energy- and water-intensive. The advantages of using alternative polymerization routes based on actinic radiation are thus clear and include lower energy consumptions, increased processing speeds and smaller plant space. However, example current drawbacks include issues related to the loss of substrate fl exibility, breathability and hand. In order to overcome these issues, a durable surface treatment has been developed based on UV-curable polymeric materials that provide superhydrophobic and oleophobic properties to cotton substrates, maintaining intrinsic useful properties of cotton fabrics such as pleasant hand. In this article are reported the innovative surface treatment formulations and procedures developed. © 2016 Scrivener Publishing LLC.

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