Efeito do tamanho de grão e concentração de cerâmico em compósitos de Poli (Fluoreto de Vinilideno) - cerâmico

Tese de doutoramento CiênciasNeste trabalho, utilizaram‐se compósitos de poli (fluoreto de vinilideno)/ Titanato Zirconato de Chumbo (PVDF/PZT) e poli (fluoreto de vinilideno)/ Titanato de Bário (PVDF/BaTiO3), com fracção volumétrica x e conectividade (0–3). Os tamanhos médios das partículas de PZT foram de 0,84, 1,68, e 2,35 μm, enquanto para o BaTiO3 foram de 10 e 500 nm. A percentagem volúmica de PZT, para os filmes compósitos de PVDF/PZT, foi de 10, 20, 30 e 40 % e de 5 e 10 % em BaTiO3,para compósitos de PVDF/BaTiO3, na fase apolar α‐PVDF. Efectuou‐se Análise de Microscopia Electrónica de Varrimento (MEV), constatando‐se que o aumento da percentagem cerâmica leva à formação de agregados e à diminuição das esferulites. Ambas as fases cristalinas apresentam maior formação de agregados para percentagens superiores a 20 % de PZT. Para tamanhos menores, verificou‐se que a dispersão cerâmica na matriz polimérica é melhorada sem alteração das esferulites. A inclusão de PZT, com tamanhos de partícula mencionados, não altera significativamente a fase de cristalização do polímero. A fracção cristalina diminui, no entanto, com o aumento da percentagem cerâmica, sendo que a temperatura de fusão não é significativamente alterada. Para maior tamanho de partícula cerâmica, aumenta a temperatura inicial de degradação dos compósitos, sendo independente da concentração do mesmo. Através dos Ensaios Dieléctricos (ED), verificou‐se um aumento da constante dieléctrica com o aumento da concentração do cerâmico, sendo significativamente menor a variação da constante dieléctrica para as contribuições do tamanho de partícula e da fase do polímero. Foi igualmente verificada a existência das seguintes relaxações: relaxação β, cerca dos ‐40 oC, associada à transição vítrea e relaxação α, depois dos 30 oC, relacionada com a componente cristalina, sendo que ambos os processos de relaxação são afectados pelo conteúdo e tamanho das partículas, tal como a condutividade típica do PVDF. Verificou‐se que o módulo de Young aumenta para compósitos com maior percentagem de cerâmico e para maior tamanho de grão. Na análise ED, verificou‐se a existência da relaxação de Maxwell‐Wagner‐ Sillars (MWS). Repetiram‐se as análises, efectuadas para os compósitos de PVDF/PZT, nos compósitos PVDF/BaTiO3, e verificou‐se não existirem diferenças estruturais, moleculares, térmicas, mecânicas e dieléctricas significativas, quando comparados com os do primeiro, exceptuando uma maior nucleação da fase electroactiva do polímero para os tamanhos de grão mais pequenosIn this work, poly (vinylidene fluoride)/Lead Zirconate Titanate (PVDF/PZT) and poly (vinylidene fluoride)/Barium Tinatate (PVDF/BaTiO3) composites of volumetric fractions x and (0–3) type connectivity were prepared. PZT powder of crystallite medium size of 0,84, 1,68, and 2,35 μm, and BaTiO3 powder of crystallite medium size of 10 and 500 nm, in different amounts of PZT (10, 20, 30, and 40 %), and BaTiO3 (5 and 10%), were mixed with the polymeric matrix. The crystalline phase of the polymeric matrix was the nonpolar α‐ phase. A Scanning Electron Microscopy (SEM) analysis was carried out and it was verified that the ceramic percentage increase leads to the formation of aggregates and spherulites decrease. Both crystalline phases present a greater aggregate formation for percentages higher than 20 percent of PZT. For smaller sizes, it was verified that the ceramic dispersion is improved, without spherulites alteration. For PZT with mentioned sizes it was verified that the chemical structure of the polymer´s crystallization phase was not affected. The crystalline fraction of the polymer is smaller for a higher percentage of the ceramic, although the fusion temperature is not significantly altered. For higher sizes of ceramic particles is verified a growth of the initial degradation temperature of the composites, being independent to the content of the same composites. Through Dielectric Analysis (DE) it was verified a growth in the dielectric constant with a higher content of the ceramic particles, being the variation of the same constant significantly lower for the contributions of the composite respective size and phase. It was verified the existence of the following relaxations: β, around ‐40 oC, associated to the glass transition, and α relaxation above 30 oC, related to the crystalline component, being both relaxation processes affected by the content and medium size of the particles, and also by the conductivity of the pure PVDF. It was verified that the Young’s module increases for composites with an increasing ceramic medium size and percentage. With ED analysis it was verified the existence of the Maxwell‐ Wagner‐Sillars (MWS) relaxation. Several analyses were carried out for the composites of PVDF/BaTiO3 and they revealed no significant structural, molecular, thermal, mechanical, and dielectric differences when compared with those of PVDF/PZT, except a higher nucleation of the electroactive phase for the polymers of smaller grain sizes

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Effect of the ceramic grain size and concentration on the dynamical mechanical and dielectric behavior of poly(vinilidene fluoride)/Pb(Zr 0.53Ti0.47)O3 composites

In this work, poly(vinilidene fluoride)/Pb(Zr0.53Ti 0.47)O3([PVDF]1-x /[PZT] x ) composites of volumetric fractions x and (0-3) type connectivity were prepared in the form of thin films. PZT powder of crystallite size of 0.84, 1.68, and 2.35 μm in different amounts of PZT (10, 20, 30, and 40%) was mixed with the polymeric matrix. The crystalline phase of the polymeric matrix was the nonpolar α-phase and the polar β-phase. Dielectric and dynamic mechanical (DMA) measurements were performed to these composites in order to evaluate the influence of particle size and the amount of PZT filler with respect to the PVDF matrix. The inclusion of ceramic particles in the PVDF polymer matrix increases the complex dielectric constant and dynamical mechanical response of the composites. A similar behavior is observed for the α- or β-phase of the polymeric matrix indicating that the PVDF polymer matrix is not particularly relevant for the composite behavior. On the other hand, ceramic size and especially content play the major role in the increase of the dielectric response and the room temperature storage modulus. In particular, the storage modulus increases with increasing PZT concentration, but this increase is more pronounced, in terms of maximum value, for the sample with 2.35 μm particle size; DMA reveals two main relaxations in the analyzed samples. A low-temperature process maximum at ca. -40°C, usually labeled by β or α a associated to the T g of the polymer and the α-relaxation at temperatures above 30°C. The β-relaxation is also observed in the dielectric measurements. The models used to asses the dielectric behavior of the samples with increasing PZT concentration indicate that the particle-matrix interaction plays a relevant role, as well as the particle asymmetry and relative orientation, being the Yamada model the most appropriate to describe the composite behavior

Effect of filler size and concentration on the structure and properties of poly(vinylidene fluoride)/BaTiO3 nanocomposites

The effect of filler size and content in the thermal, mechanical and electrical response of poly(vinylidene fluoride) (PVDF)/ BaTiO3 nanocomposites has been investigated. Dielectric constant increases significantly with increasing filler content and decreasing filler size. Space charge effects at the interface between BaTiO3 and PVDF strongly influence the dielectric response. The electroactive -phase of PVDF is nucleated by the presence of the ceramic filler, the effect being strongly dependent on filler size and independent on filler content. This filler/matrix interaction is also responsible for the variations observed in the activation energy of the thermal degradation of the polymer. Smaller particles lead to larger relative contact areas and are responsible for the main variations observed in the thermal, mechanical and electrical properties of the composites.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade-COMPETE'' and by national funds by FCT-Fundacao para a Ciencia e a Tecnologia, project references PTDC/CTM/69316/2006, PTDC/CTM-NAN/112574/2009, and NANO/NMed-SD/0156/2007. The authors also thank support from the COST Action MP1003, 2010 'European Scientific Network for Artificial Muscles'. V. S., S. F. M., and C. M. C. thank the FCT for the SFRH/BPD/63148/2009, SFRH/BD/22506/2005, and SFRH/BD/68499/2010 grants, respectively

Influence of processing parameters on the polymer phase, microstructure and macroscopic properties of poly(vinilidene fluoride)/Pb(Zr0.53Ti 0.47)O3 composites

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

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 2.35 μm average size with filler contents up to 40% 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 a-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.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade - COM-PETE" and by national funds by FCT-Fundacao para a Ciencia e a Tecnologia, project references PTDC/CTM/69316/2006, PTDC/CTM-NAN/112574/2009, and NANO/NMed-SD/0156/2007. V. S., S. Firmino Mendes and C. M. Costa thank the FCT for the SFRH/BPD/63148/2009, SFRH/BD/22506/2005 and SFRH/BD/68499/2010 grants, respectively. JLGR acknowledge the support of the Spanish Ministry of Education through project No. MAT2007-66759-C03-01 (including the FEDER financial support), and founding in the Centro de Investigacion Principe Felipe in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana), and the Instituto de Salud Carlos III (Ministry of Science and Innovation). The authors thank the support from the COST Action MP1003, 2010, 'European Scientific Network for Artificial Muscles' (ESNAM)

3D Reconstruction and Prediction of Sialolith Surgery

Imaging examinations play an important role in the diagnosis of sialolithiasis, whose symptoms are initially confounded with other diseases. The objective of the present case report is to highlight imaging and processing techniques as well as image analysis for the preoperative assessment and planning of surgical interventions and adequate treatment of massive sialoliths. A 35-year-old male patient presented complaining of pain in the submandibular region and purulent secretions from a lingual caruncle with slightly increased volume in the region. Imaging examinations were ordered as follows: cone beam computed tomography, ultrasonography, and three-dimensional reconstruction, including clinical evaluation. A final diagnosis of sialolithiasis was established. Surgery was indicated and carried out by using a lateral transcervical approach for complete resection of the gland, which was based on the calculation of the total volume of the sialolith, thus increasing the surgery’s success