C.M. Costa

Influence of filler size and concentration on the low and high temperature dielectric response of poly(vinylidene fluoride) /Pb(Zr0.53Ti0.47)O3 composites

Poly(vinylidene fluoride)/Pb(Zr0.53Ti0.47)O3([PVDF]1 − x/[PZT]x ) composites of volume fractions x and (0–3) type connectivity were prepared in the form of thin films. The films were prepared by solvent casting with PZT powder of 0.84, 1.86, and 2.35xa0μm average size with filler contents up to 40xa0% volume. The crystalline phase of the polymer matrix was the nonpolar α-phase and the polar β-phase. Dielectric measurements were performed in order to evaluate the influence of the filler size and content as well as the effect of the polymer matrix in the overall response of the material. No nucleation effect of any of the phases was observed for the used fillers. The spherulitic structure of the pure α-PVDF and the characteristic porosity of the β-phase material are destroyed for high PZT volume fractions. The inclusion of ceramic particles in the PVDF polymer matrix increases the complex dielectric constant of the composites independently of the PVDF polymer matrix. The dielectric properties of the composites are mainly affected by the amount of the ceramic particles. With respect to the relaxation processes of the polymer, the activation energy of the αa-relaxation increases and the glass transition temperature decreases with increasing particle size and content. The high-temperature conductivity decreases with increasing filler content and there is an important contribution of the Maxwell-Wagner-Sillars effect to the overall dielectric response.

Thermal Properties of Electrospun Poly(Lactic Acid) Membranes

Poly(lactic acid) (PLA) electrospun membranes were obtained by electrospinning and characterized by scanning electron microscopy (SEM) and thermal analysis. The polymer membranes showed a random fiber distribution with a mean diameter of 1 μm (±300 nm). Differential scanning calorimetry (DSC) experiments showed that the membranes had a glass transition, cold crystallization, and melting temperatures of 54, 90, and 151°C, respectively. The kinetic study of thermal degradation of PLA under a nitrogen atmosphere was performed by means of thermogravimetry (TGA). It was found that the thermal decomposition kinetics of PLA could be interpreted in terms of a multi-step degradation mechanism. Several theoretical models were applied to the TGA data. The activation energies obtained by the Broido and Ozawa–Flynn–Wall (OFW) models were in good agreement with the value of the activation energy calculated by the Kissinger method.

Functionally graded electroactive Poly(vinylidene fluoride) polymers

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.

Evaluation and optimization of the performance of frame geometries for lithium-ion battery application by computer simulation

Tailoring battery geometries is essential for many applications, as geometry influences the delivered capacity value. Two geometries, frame and conventional, have been studied and, for a given scan rate of 330C, the square frame shows a capacity value of 305,52 Ahm−2, which is 527 times higher than the one for the conventional geometry for a constant the area of all components.

Thermal analysis of lithium-ion batteries with square frame geometries by theoretical simulations

Portuguese Foundation for Science and Technology (FCT) in the nframework of the Strategic Funding UID/FIS/04650/2013. n The authors thank FEDER funds through the nCOMPETE 2020 Programme and National Funds through nFCT - Portuguese Foundation for Science and nTechnology under the projects PTDC/CTM-ENE n/5387/2014 and UID/CTM/50025/2013 and grants nSFRH/BPD/112547/2015 (C.M.C.). SLM thanks financial nsupport from the Basque Government Industry nDepartment under the ELKARTEK nProgram. F. Miranda was also n supported by Portuguese funds nthrough the CIDMA - Center for Research and Development in Mathematics a nnd Applications, and the nPortuguese Foundation for Science and Technology (“FCT - Fundacao para a Ciencia e a Tecnologia”), nwithin project UID/MAT/04106/2013