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A. C. Lopes

Other affiliations: University of Porto
Bio: A. C. Lopes is an academic researcher from University of Minho. The author has contributed to research in topics: Dielectric & Crystallization. The author has an hindex of 18, co-authored 29 publications receiving 2679 citations. Previous affiliations of A. C. Lopes include University of Porto.

Papers
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Journal ArticleDOI
TL;DR: In this article, the main characteristics of the electroactive phases of polyvinylidene fluoride and copolymers are summarized, and some interesting potential applications and processing challenges are discussed.

2,242 citations

Journal ArticleDOI
TL;DR: In this paper, the piezoelectric d33 response of montmorillonite clay was measured and the obtained value of d33 is −7 pC/N, lower than in β-PVDF obtained by mechanical stretching but still among the largest coefficients obtained for polymers.
Abstract: Poly(vinylidene fluoride), PVDF, based nanocomposites with different clay structures have been processed by solvent casting and melt crystallization. Depending on the melting temperature of the polymer, the nanocomposite recrystalises in the electroactive γ or nonelectroactive α phase of the polymer. This fact is related to the thermal behavior of the clay. For montmorillonite clay, the full crystallization of the electroactive γ phase occurs for clay contents lower than 0.5 wt %, allowing the nanocomposites to maintain the mechanical properties of the polymer matrix. The electroactivity of the material has been proven by measuring the piezoelectric d33 response of the material. The obtained value of d33 is −7 pC/N, lower than in β-PVDF obtained by mechanical stretching but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. Finally, it is demonstrated that the nuclea...

245 citations

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TL;DR: In this article, the authors investigated the dielectric function, ac conductivity and electric modulus of polyvinylidene fluoride/zeolite composites prepared by solvent casting at 190°C.

100 citations

Journal ArticleDOI
TL;DR: Aluminosilicates have traditionally been important materials for applications related to adsorbents, water softeners, catalysis and mechanical and thermal reinforcement due to their high surface area, excellent thermal/hydrothermal stability, high shape-selectivity and superior ion exchange ability.

81 citations

Journal ArticleDOI
TL;DR: In this article, the effect of different ionic liquids (ILs) on the electroactive β-phase, thermal, mechanical and electrical properties of the polyvinylidene fluoride (PVDF) blend was evaluated.

69 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the main characteristics of the electroactive phases of polyvinylidene fluoride and copolymers are summarized, and some interesting potential applications and processing challenges are discussed.

2,242 citations

Journal ArticleDOI
TL;DR: This Review presents a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications.
Abstract: Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

1,143 citations

Journal ArticleDOI
TL;DR: In this article, a universal phase identification procedure using only the Fourier transform infrared spectroscopy (FTIR) results is proposed and validated, which can differentiate the three phases by checking the bands around 763 and/or 614, 1275, and 1234 cm−1 for the α, β and γ phases, respectively.
Abstract: Poly(vinylidene fluoride) (PVDF) has been widely utilized in scientific research and the manufacturing industry for its unique piezoelectric properties. In the past few decades, the vibrational spectra of PVDF polymorphic polymers via FTIR (Fourier transform infrared spectroscopy) have been extensively investigated and documented. However, reports on the analysis of α, β and γ phases often have conflicting views based on measured data. In this work, we analyze the FTIR vibrational bands of PVDF materials fabricated by different processes with detailed XRD (X-ray diffraction) characterization to identify the structural α, β and γ phases. By examining the results in this work and extensively reviewing published research reports in the literature, a universal phase identification procedure using only the FTIR results is proposed and validated. Specifically, this procedure can differentiate the three phases by checking the bands around 763 and/or 614, 1275, and 1234 cm−1 for the α, β and γ phases, respectively. The rule for assignment of the 840* and 510* cm−1 bands is provided for the first time and an integrated quantification methodology for individual β and γ phase in mixed systems is also demonstrated.

779 citations

Journal ArticleDOI
TL;DR: This study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries.
Abstract: Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use Li6.75La3Zr1.75Ta0.25O12 (LLZTO) ceramics to trigger structural modification of poly(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and C═O group of solvent molecules such as N,N-dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane (e.g., a high ionic conductivity of about 5 × 10–4 S cm–1 at 25 °C, high mechanical s...

617 citations

Journal ArticleDOI
TL;DR: A simple and versatile in situ fabrication of MAPbX3 nanocrystal-embedded polymer composite films is developed by controlling the crystallization process from precursor solutions, exhibiting enhanced photoluminescence properties, improved stability, and excellent piezoelectric and mechanical properties.
Abstract: A simple and versatile in situ fabrication of MAPbX3 nanocrystal-embedded polymer composite films is developed by controlling the crystallization process from precursor solutions. The composite films exhibit enhanced photoluminescence properties, improved stability, and excellent piezoelectric and mechanical properties. Applications of these composite films as color converters in liquid-crystal-display backlights are demonstrated, showing bright potential in display technology.

587 citations