Estudo da relação entre a resposta piezoeléctrica macro-e microscópica do poli(fluoreto de vinilideno)

Dissertação de mestrado em Engenharia de MateriaisNa vasta gama dos polímeros, o poli(fluoreto de vinilideno) (PVDF), é o que reúne as propriedades piezo, piro e ferroeléctricas mais interessantes do ponto de vista científico e tecnológico. Assim sendo, o objectivo deste trabalho consistiu em estudar e caracterizar a resposta piezoeléctrica deste polímero, quer na escala microscópica quer na macroscópica, relacionando posteriormente ambas as respostas de forma a entender os processos físicos envolvidos nas diferentes. Isto permitirá uma melhor compreensão e eventual controlo das propriedades finais deste polímero. Deste modo foram estudados dois tipos de amostras, a primeira possuindo a fase mais estável deste polímero quando obtida por cristalização do fundido (fase α), a segunda foi obtida por estiramento da primeira amostra a uma temperatura de 80ºC, intitulada de fase β. Esta segunda amostra foi estudada antes e após do processo de polarização, i.e., da aplicação de um campo eléctrico, induzindo a orientação dos dipólos na direcção deste campo, obtendo-se assim amostras polarizadas. Para além das medidas dieléctricas realizadas em todas estas amostras, à temperatura ambiente, a resposta piezoeléctrica macroscópica foi obtida por dois métodos diferentes: o primeiro por interferometria óptica, que foi idealizado e desenvolvido utilizando como referência um interferómetro de Michelson, sendo este modificado de forma a obter uma maior resolução do sistema; e o segundo por medidas electromecânicas constituído por um detector capacitivo, um circuito de Sawyer-Tower e um integrador, ambos determinando a contribuição da parte electroactiva de toda a área da amostra. Com recurso à Microscopia de Força Atómica, obteve-se a morfologia e rugosidade das várias fases do PVDF. A resposta piezoeléctrica microscópica foi obtida através do modo de Microscopia de Força Piezoeléctrica, visualizando as diferentes distribuições dos domínios piezoeléctricamente activos em cada uma das fases, assim como o efeito da polarização na amostra em fase beta. Igualmente foi estudada a distribuição de zonas cristalinas e amorfas das amostras polarizadas. Desta forma foi possível estudar e compreender a relação existente entre as diferentes escalas da resposta piezoeléctrica do PVDF, verificando-se que esta resposta surge sempre na fase β enquanto na macroscópica está presente apenas na fase β quando os dipólos se encontram orientados na direcção do campo eléctrico.Poly(vinylidene fluoride) (PVDF) is the polymer with the most interesting piezo-, pyro-, and ferroelectric properties, both from a scientific and a technological standpoint. In this way, the goal of this work was to study and characterize the piezoelectric response of this polymer both at a microscopic and macroscopic level, relating both responses in order to understand the main physical processes present at the different scales and their influence in the final proprieties of the polymer. Two types of samples were studied in this work: samples in the α phase, which is the most stable phase in this polymer when crystallized from the melt, and β phase samples obtained by stretching α-phase samples at 80ºC. The last samples were also studied in the poled form, i.e. after applying an electric field in order to orient the dipoles in the direction of the applied field. Together with dielectric measurements at room temperatures, the macroscopic piezoresponse of the samples was obtained by two different methods. The first one was by optical interferometry, using a modified Michelson interferometer in order to obtain a higher resolution from this system; the second one used electromechanical measurements performed by a capacitive detector, a Sawyer-Tower circuit and an integrator, both determining the contribution of the electroactive part from the area of the samples. With the help of Atomic Force Microscopy (AFM), it was possible to obtain the morphology and roughness of the samples at different scales. The microscopic piezoelectric response was obtained using the Piezoelectric Force Microscopy (PFM) mode, visualizing the electric domain distribution in each PVDF phase and performing an assessment of crystalline and amorphous phase distribution of the poled sample. It was possible to study and understand the relationship between the piezoelectric response of PVDF at the macroscopic and microscopic scales. The microscopic response is present in the β phase samples but it appears only macroscopically after the sample is poled, since the orientation of the dipole moment changes the dipole and therefore domain distribution

Information security frameworks for assisting GDPR compliance in banking industry

Purpose: Data can nowadays be seen as the main asset of organizations and data leaks have a considerable impact on the organization’s image, revenues and possible consequences to the affected clients. One of the most critical industries is the bank. Information security frameworks (ISF) have been created to assist organizations and other frameworks evolved to update these domain practices. Recently, the European Union decided to create the general data protection regulation (GDPR), applicable to all organizations dealing with personal data of citizens residing in the European Union. Although considered a general regulation, GDPR implementation needs to align with some industries’ laws and policies. Especially in the Bank industry. How these ISF can assist the implementation of GDPR is not clear. Design/methodology/approach: The design science research process was followed and semi-structured interviews performed. Findings: A list of practices to assist the bank industry in GDPR implementation is provided. How each practice map with assessed ISF and GDPR requirements is also presented. Research limitations/implications: As GDPR is a relatively recent subject, it is hard to find experts in the area. It is more difficult if the authors intend to find experienced people in the GDPR and bank industry. That is one of the main reasons this study does not include more interviews. Originality/value: This research provides a novel artefact to the body of knowledge. The proposed artefact lists which ISF practices banks should implement to comply with GDPR. By doing it the artefact provides a centralized view about which ISF frameworks (or part of them) could be implemented to help banks comply with GDPR.info:eu-repo/semantics/acceptedVersio

Electrical and microstructural changes of β-PVDF under uniaxial stress studied by scanning force microscopy

Chain reorientation may be induced in polyvinylidene fluoride (PVDF) in its β-phase by applying a deformation perpendicular to the pre-oriented polymeric chains. This reorientation begins right after the yielding point and seems to be completed when the stress-strain curve stabilizes. As the deformation process plays an important role in the processing and optimisation properties of the material for practical applications, different deformation stress was applied to the PVDF lamellas and their topographic change and piezoelectric response were studied by means of scanning force microscopy in a piezo-response mode. The experimental results confirm the previously observed chain reorientation that occurs right after the yielding point and that is completed when the yielding region is passed. This reorientation is accompanied by a stretching of the granular structures observed in the topographical images and variations in the domain response. The observed results help to explain the variations in the macroscopic response of the material.Fundação para a Ciência e a Tecnologia (FCT) - Grant POCTI/CTM/33501/99, POCI/CTM/59425/2004.Measurement Specialties Inc

Piezoelectric and optical response of uniaxially stretched (VDF/TrFE) (75/25) copolymer films

The phase diagram of the poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) copolymer system shows for VDF contents of 50...85 mol% a ferroelectric (FE)-paraelectric (PE) phase transition below melting temperature. Investigations on P(VDF-TrFE) 75/25 samples revealed a slight anisotropic behaviour, which leads to a strongly anisotropic stretching effect both on the phase transition and on the amount and nature of the FE phase in samples subjected to mechanical stretching along the main directions of the film. In this work, both the refractive index n1,2 and the piezoelectric coefficient d33 of mechanically stretched P(VDF-TrFE) have been measured for samples with different levels of permanent deformation. These parameters are found to reflect the anisotropy of the permanently deformed samples. The stretching effect is most pronounced (n1,2) or limited (d33) to the vicinity of the yielding point of the material. Above the yielding point, almost the piezoelectric d33 coefficient of the non-deformed sample is observed for samples with large permanent deformation.Fundação para a Ciência e a Tecnologia (FCT) - Grants POCTI/CTM/33501/99, POCI/CTM/59425/2004.PIEZOTECH S.A.CRUP (AI-A-16/04)

Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines, December 2012

Category 5 (C5) Super Typhoon Bopha, the world’s worst storm of 2012, formed abnormally close to the West Pacific Equator, and Bopha’s Mindanao landfall has the record equatorial proximity for C5 storms. Bopha generated a debris flow that buried 500 ha of New Bataan municipality and killed 566 people. New Bataan, established in 1968, had never experienced super typhoons and debris flows. We describe the respective histories of New Bataan and Super Typhoon Bopha; debris flows; and how population growth and unwise settlement practices contribute to Philippine “natural” disasters. The historical record of Mindanao tropical cyclones yields clues regarding how climate change may be exacerbating near-equatorial vulnerability to typhoons. Existing models of future typhoon behavior do not apply well to Mindanao because they evaluate only the tropical cyclones that occur during the main June–October typhoon season, and most Mindanao tropical cyclones occur in the off season. The models also ignore tropical depressions, the most frequent—and commonly lethal—Mindanao cyclones. Including these in annual tallies of Mindanao cyclones up to early 2018 reveals a pronounced and accelerating increase since 1990. Mindanao is susceptible to other natural hazards, including other consequences of climate change and volcanic activity

Oral POLYMER BASED ELECTRO-ACTIVE MICRO-AND NANO-COMPOSITES

Abstract Polymeric materials filled with micro and nanoparticles have been widely investigated in the last few years. Till recently, mainly the mechanical reinforcement effect of these nanofillers was highlighted. Nowadays, several composites and nano-composites of electroactive polymers have been investigated due to their potential applications. In this way, carbon nanotubes/ polymer nanocomposites with high dielectric constant; electroactive polymers with metallic nanoparticles in order to tune electro-optic properties, magnetostrictive nanoparticles inducing magntoelectric response, and the introduction of ceramic microparticles to tune dielectric and piezoelectric properties have been investigated. In order to achieve the desired electromechanical, magnetoelectric and electro-optical properties, the composites have to poled The general issues related to the processing of the electroactive composites such as dispersion, stretching and poling will be presented and discussed. The influence of these parameters on some key macroscopic properties such as the electrical and mechanical properties will be also presented. Particular attention will be drawn on the stretching and poling process necessary to achieve NanoSpain2008 14-18 April, 2008 Braga-Portugal Oral polar β-phase within the polymeric matrix, as this critical step shows specific issues within the different nanocomposites. Acknowledgement

HIV-1-Transmitted Drug Resistance and Transmission Clusters in Newly Diagnosed Patients in Portugal Between 2014 and 2019

Objective: To describe and analyze transmitted drug resistance (TDR) between 2014 and 2019 in newly infected patients with HIV-1 in Portugal and to characterize its transmission networks. Methods: Clinical, socioepidemiological, and risk behavior data were collected from 820 newly diagnosed patients in Portugal between September 2014 and December 2019. The sequences obtained from drug resistance testing were used for subtyping, TDR determination, and transmission cluster (TC) analyses. Results: In Portugal, the overall prevalence of TDR between 2014 and 2019 was 11.0%. TDR presented a decreasing trend from 16.7% in 2014 to 9.2% in 2016 (p for-trend = 0.114). Multivariate analysis indicated that TDR was significantly associated with transmission route (MSM presented a lower probability of presenting TDR when compared to heterosexual contact) and with subtype (subtype C presented significantly more TDR when compared to subtype B). TC analysis corroborated that the heterosexual risk group presented a higher proportion of TDR in TCs when compared to MSMs. Among subtype A1, TDR reached 16.6% in heterosexuals, followed by 14.2% in patients infected with subtype B and 9.4% in patients infected with subtype G. Conclusion: Our molecular epidemiology approach indicates that the HIV-1 epidemic in Portugal is changing among risk group populations, with heterosexuals showing increasing levels of HIV-1 transmission and TDR. Prevention measures for this subpopulation should be reinforced.info:eu-repo/semantics/publishedVersio

Influence of the β−phase content and degree of crystallinity on the piezo- and ferroelectric properties of poly (vinylidene fluoride)

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 ºC has been studied. Stretching ratio and temperature deeply influences 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 depend 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.Authors want to express their thanks to Solvay for the excellent material provided and to Portuguese Foundation for Science Technology – FCT for financial support (Grant POCI/CTM/59425/2004, PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007). V. Sencadas acknowledges the FCT for Grant (SFRH/BD/16543/2004 and SFRH/BPD/63148/2009)

Piezoelectric beta-PVDF polymer films as fluid acoustic microagitator

The main objective of this paper is to describe a fluidic acoustic microagitation system based on a Poly(Vinylidene Fluoride) polymer. This system benefits from the high piezoelectric properties presented by the beta-phase of the polymer (beta-PVDF) converting an electrical signal into acoustics vibrations. These vibrations can be used in microfluid systems to enhance fluids mixture and reaction. Experimental results regarding the influence of the area and thickness of the piezoelectric beta-PVDF polymer on the velocity of reaction of some biological fluids are presented. Moreover, the incorporation of the beta-PVDF underneath microfluidic structures of a lab-on-a-chip with an automatic electronic control is referred.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/BIO/70017/2006 and POCI/CTM/59425/2004

A lab-on-a-chip for clinical analysis with acoustic microagitation based on piezoelectric poly (Vinylidene Fluoride)

This paper reports on the incorporation and validation of a microagitation system based on a piezoelectric polymer, Poly(vinylidene fluoride) in its beta phase, β-PVDF, in a fullyintegrated disposable lab-on-a-chip for point-of-care testing and monitoring of biochemical parameters in biological fluids. The lab-on-a-chip concept offers a novel approach for clinical analyses, especially in biological fluids analyses, due to its portability, ensuring that the analysis can be performed at any location with quick results. Its microagitation system performance was successfully demonstrated by quantitative measurements of uric acid in human urine, thought other molecules or biological fluids can be also measured. The optimization tests prove that it is possible to use lower frequencies than resonance with no major changes in the mixing process. The effect of area and location within the lab-on-a-chip of the microagitation system was also considered.Portuguese Foundation for Science and Technology (grants PTDC/BIO/70017/2006 and PTDC/CTM/69362/2006)