Development of mechanical, electrical and electromechanical properties of copolymer styrene-butadiene-styrene with carbon nanotubes composites

Tese de doutoramento (Programa Doutoral em Engenharia de Materiais)Composites are an important class of materials as they allow to reinforce or to include specific properties not typically found in nature. In this way, suitable electromechanical materials allow the measurement of large deformations by electrical means can be achieved by the development of composites. Research in electromechanical composites has been based in several polymer matrices with carbon nanoallotropes to increase the electrical conductivity of the composites. Successful development of electromechanical transducer materials has been accomplished, but reliable solutions for the development of large deformation sensors are still to be developed to meet the increasing industrial needs. This work is focused on the study of the electromechanical response of carbon nanotubes/thermoplastic elastomers (CNT/TPE) composites with the main goal of maximizing sensitivity and deformation (> 30%) in order to improve the application range of the composites for sensor applications. The composite materials used in these work are four different tri-block copolymers styrene-butadiene-styrene (SBS) (with reference C401, C411, C500 and C540) where the block copolymer structure is linear or radial and butadiene/styrene ratio ranged between 80/20 to 60/40. The composites materials are prepared by three different processing methods: solvent casting, extrusion and electrospinning. The amount of CNT included in the composites prepared by the different processing methods are 0, 1, 2, 4 and 8 weight percentage (wt%) for solvent casting, 0, 2, 4, 6, 8 and 10 wt% for extruded composites and 0, 0.05, 0.1 and 0.5 wt% for electrospun composites. It was important to find the electrical percolation threshold to obtain suitable electromechanical responses for sensors applications. Different types of CNT such as single walled CNT (SWCNT) and multi walled CNT (MWCNT) were used to study electrical and electromechanical properties of the composites. Chemical treatment of the CNT was also performed to understand the effect of functionalization on CNT dispersion and in the electromechanical response of the CNT/SBS composites. Covalent and non-covalent functionalization on MWCNT has been used for filler concentrations up to 8 wt%. SBS shows maximum strain larger than 1000% both for pure SBS and the both composites prepared by solvent casting and extrusion. On the other hand, composites prepared by electrospinning show a maximum strain of 350%. The ratio of butadiene/styrene in the copolymer and the different copolymer architecture mainly influences the mechanical properties. Initial modulus is larger for matrices with higher amounts of styrene and for CNT/SBS composites increases with increasing CNT content, independently of the composite processing method. Mechanical hysteresis of the composite increases with applied strain (from 5% to 20%) and decreases with increasing the number of stress-strain cycles. Softer matrices (higher amount of butadiene) have lower mechanical hysteresis than harder matrices (higher amounts of styrene), demonstrating the influence of the butadiene/styrene ratio on the mechanical properties of the composites. Morphological evaluation of the composites shows well dispersed clusters of CNT inside SBS matrices for pristine CNT and individual dispersion of functionalized CNT within the SBS matrices. The percolation theory concludes that hopping between nearest fillers is considered as the main mechanism for the composite electrical conduction, the overall composite conductivity is explained by the existence of a weak disorder regime. The amount of pristine CNT inside the SBS matrix improves electrical properties of the composites, the electrical percolation threshold being lower than 1 wt% CNT for composites prepared by solvent casting and electrospinning processing methods, increasing up to 4-5 wt% CNT content for extruded composites. Composites with covalent and non-covalent functionalization, do not present electrical percolation threshold for filler contents up to 8 wt% CNT, where conductivity remains similar to pure SBS matrix. The electromechanical properties of the composites depend on composite fillers content, CNT functionalization state and processing methods. Uniaxial strain and 4-pointbending measurements for solvent casting composites show larger electromechanical response for all matrices with maximized sensibility after initial pre-stress. The Gauge Factor (GF) for solvent casted composites with 4 wt% CNT filler content can reach values of GF~120 for C540 samples under uniaxial strain and GF~100 for C401 samples under 4-point-bending mechanical solicitation. For extruded composites with 8 wt% CNT, they reach a value of ~30 for C401 SBS under uniaxial strain. The maximum deformation with suitable electromechanical response can reach 50% of strain. The proof of concept of the composites for sensor applications has been performed with the development of a glove with finger movement monitoring.Compósitos são atualmente uma importante classe em materiais e possibilitam obter propriedades únicas não presentes na natureza. Seguindo esta ideia, podem ser desenvolvidos materiais com propriedades electromecânicas para medir grandes deformações mecânicas através da resposta elétrica. A procura destes compósitos eletromecânicos é baseada em diversas matrizes poliméricas com o reforço dos diversos nanomateriais carbonáceos. O presente trabalho é focado no estudo da resposta eletromecânica de compósitos nanotubos de carbono/termoplásticos elastómeros tendo como objectivo principal maximizar a sensibilidade eletromecânica e a deformação (> 30%), alargando o leque de aplicações destes compósitos. Os materiais utilizados neste trabalho são quatro diferentes copolímeros de estirenobutadieno- estireno (com a referencia C401, C411, C500 e C540), utilizados como matriz, tendo o copolímero estrutura linear ou radial e rácio butadieno/estireno varia entre 60/40 e 80/20. Como material de reforço são usados três diferentes tipos de nanotubos de carbono, de parede simples ou múltipla com a referência C150P, NC7000 e AP-SWNT. Os compósitos foram preparados por três métodos: a partir da dissolução num solvente, por electrospinning e extrusão. A quantidade, em massa, de nanotubos de carbono presente nos compósitos foi de 0, 1, 2, 4 e 8% para o processamento a partir da solução, de 0, 2, 4, 6, 8 e 10% para o processamento por extrusão, e de 0, 0.05, 0.1 e 0.5% para os materiais processados por electrospinning. As várias concentrações foram utilizadas de forma a determinar o limite de percolação elétrico dos compósitos, de forma a otimizar a resposta eletromecânica destes. Os nanotubos de carbono também foram alvo de funcionalização, covalente e não-covalente, com o intuito de entender a evolução das propriedades dos compósitos com os diferentes nanotubos e funcionalizações destes. Compósitos até 8% em massa de nanotubos foram processados a partir de um solvente com nanotubos de carbono funcionalizados. As matrizes poliméricas apresentam excelentes propriedades mecânicas com a deformação máxima a variar entre 350% para os materiais processados por electrospinning e mais de 1000% para os compósitos preparados com os restantes tipos de processamento. O rácio butadieno/estireno influencia essencialmente as propriedades mecânicas e o módulo elástico aumenta com a quantidade de estireno e de nanotubos de carbono na matriz, independentemente do processamento utilizado. A histerese mecânica aumenta com a deformação e diminui com o número de ciclos tensãodeformação aplicados no compósito, sendo maior para as matrizes com maior quantidade de estireno no copolímero. A morfologia dos compósitos é similar para os nanotubos de carbono sem tratamento, apresentando uma boa dispersão de agregados de nanotubos de carbono. Os compósitos com os nanotubos de carbono funcionalizados apresentam uma dispersão individual de nanotubos de carbono em vez de uma dispersão de agregados. A teoria da percolação mostra que o hopping entre os nanotubos vizinhos é considerado o principal mecanismo de condução elétrica no compósito, e a condutividade total do compósito pode ser explicada pela existência de um regime de fraca desordem. O aumento de nanotubos de carbono não funcionalizados na matriz polimérica melhora as propriedades elétricas do compósito sendo o limite de percolação elétrico menor que 1% em massa para os compósitos processados a partir do solvente e por electrospinning e cerca de 4-5% para os compósitos processados por extrusão. Os compósitos usando nanotubos de carbono funcionalizados não apresentam percolação elétrica. As propriedades eletromecânicas do compósito dependem da quantidade de nanotubos de carbono na matriz e do método de processamento. As medidas para a deformação unidireccional e a flexão de 4 pontas para compósitos processados a partir de solução no solvente apresentam uma boa resposta eletromecânica para as quatro matrizes poliméricas, tendo a sua sensibilidade maximizada após pré-deformação. O Factor de Gauge para os compósitos com 4%, em massa, de nanotubos de carbono é cerca de 120 e 100 para a matriz C540 medida pelo método de deformação unidireccional e de flexão de 4 pontas, respectivamente. Para compósitos processados por extrusão, com 8% em massa, o Factor de Gauge máximo é cerca de 30, para a matriz C401 medido na deformação unidireccional. A deformação máxima com uma boa resposta eletromecânica é de 50% nestes compósitos. A prova de conceito da utilização destes compósitos para aplicações de sensores foi realizada através do desenvolvimento de uma luva com a monitorização do movimento dos dedos

Estudo das propriedades mecânicas, eléctricas e térmicas do compósito poli(fluoreto de vinilideno)/nanotubos de carbono

Tese de mestrado em Física dos Materiais Avançados (área de especialização em Materiais Funcionais para Nano e Microtecnologias)Nos últimos anos os compósitos têm vindo a ser crescentemente estudados na procura de materiais que tenham excelentes propriedades para aplicações específicas que num único material não se encontram. Um dos compósitos mais estudados tem sido os formados por materiais condutores numa matriz isoladora para variar a resposta eléctrica do compósito. Esta tese foi realizada com o objectivo de estudar as propriedades mecânicas, térmicas e eléctricas de compósitos de nanotubos de carbono/polímero com propriedades electroactivas. Os nanotubos de carbono são de parede múltipla (MWCNT) e o polímero é o poli(fluoreto de vinilideno)- PVDF. Um dos principais objectivos é o estudo da constante dieléctrica destes compósitos perto do limite de percolação. O método de preparação usado é importante para obter bons resultados como homogeneidade e elevada constante dieléctrica. O método de preparação dos compósitos nesta tese consiste na dispersão dos nanotubos de carbono com o uso do tolueno e a eliminação dos seus defeitos pela técnica de descarga em corona antes destes se juntarem ao polímero. Foi processado o compósito nanotubos de carbono/PVDF na fase α (α- MWCNT/PVDF) por solução e posteriormente foi aplicado o processo de estiramento para se obter o compósito nanotubos de carbono/PVDF na fase β (β-MWCNT/PVDF). A inclusão de nanotubos de carbono representa um reforço mecânico no que respeita às propriedades do polímero e aumenta o grau de cristalinidade nos compósitos. Por outro lado a fracção de fase β máxima atingida é 60%, quando no polímero chega a ser superior a 85%. Termicamente a inclusão de nanotubos de carbono aumenta a estabilidade dos compósitos em relação ao polímero e a degradação é similar para ambos. Com o aumento da concentração de MWCNT temos um aumento da condutividade eléctrica nos compósitos e um decaimento exponencial da rigidez dieléctrica. A constante dieléctrica do compósito é ε’~ 1300 para 2% e de ε’~ 3000 para 4.8% de MWCNT no compósito α-MWCNT/PVDF. Para o compósito β- MWCNT/PVDF a constante dieléctrica é sempre maior que a do polímero (ε’~ 10) mas sempre inferior a ε’~ 100. Variando o método de preparação são obtidas grandes variações na resposta dieléctrica dos compósitos.In recent years, composites have been increasingly studied in the search for materials with tailored properties for specific applications that cannot be found in a single material. Among the most studied composites are the ones formed by conductive materials in an insulating matrix in order to tune the electrical response of the composite. This work was undertaken with the aim of studying the mechanical, thermal and electrical properties of carbon nanotubes/ electroactive polymer composites. In particular composites from multi walled carbon nanotubes (MWCNT) with poly (vinylidene fluoride)- PVDF- were prepared. A major objective of this work is the study of the dielectric response of the composites near the percolation threshold. The method of preparation of this composites is important in order to get homogeneous distribuition of the fillers and high dielectric constant of the composites. In this work the processing method involved the use of toluene for improving dispersion of the carbon nanotubes and corona discharge for removal of their defects. Carbon nanotube/PVDF in α phase (α-MWCNT/PVDF) composites were prepared by solution casting. Stretching of α-MWCNT/PVDF composites was applied in order to get composites in the β phase (β-MWCNT/PVDF). The inclusion of carbon nanotubes increases the mechanical strenght of the polymer with respect to the ones of the polymer. The inclusion of carbon nanotubes increases also the degree of crystallinity and thermal stability of the composites. Furthermore, the maximum fraction of β phase is 60% whereas β phase contents up to 85% are obtained for the pure polymer. With increasing MWCNT concentration the electrical conductivity of the composites is also increased and the dielectric strenght decays exponentially. The dielectric constant of the composite increases up ε '~ 1300 for 2% and ε' ~ 3000 for 4.8% of MWCNT in α-MWCNT/PVDF composite. For the β-MWCNT/PVDF composite the dielectric constant is always larger than for the polymer (ε' ~ 10) but lower than ε'~ 100. With larger variations of the dielectric response of composites are obtained by varying the processing method of the composites

Functional, lightweight materials: outlook, future trends and challenges

The growing demand for weight-saving engineering applications has led to the progress of lightweight composites with functional properties for an increasing number of applications. Lightweight materials with functional properties can be developed using a wide range of host matrices and reinforcement material. These large variety of possible combinations allow the development of new functional materials, structures and devices and that represent the present and the future of different engineering areas. Their novel properties combined with advanced manufacturing processes strongly increases the use of these materials in applications. This chapter presents some relevant challenges and an outlook on the future of this field.The authors thank the FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, UID/EEA/04436/2013 and UID/QUI/0686/2016; projects PTDC/EEI-SII/5582/2014 and PTDC/FIS-MAC/28157/2017 and grants s SFRH/BPD/110914/2015 (P.C.) and SFRH/BPD/112547/2015 (C.M.C.) Funding from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, is also acknowledged

Triboelectric energy harvesting response of different polymer-based materials

Energy harvesting systems for low-power devices are increasingly being a requirement within the context of the Internet of Things and, in particular, for self-powered sensors in remote or inaccessible locations. Triboelectric nanogenerators are a suitable approach for harvesting environmental mechanical energy otherwise wasted in nature. This work reports on the evaluation of the output power of different polymer and polymer composites, by using the triboelectric contact-separation systems (10 N of force followed by 5 cm of separation per cycle). Different materials were used as positive (Mica, polyamide (PA66) and styrene/ethylene-butadiene/styrene (SEBS)) and negative (polyvinylidene fluoride (PVDF), polyurethane (PU), polypropylene (PP) and Kapton) charge materials. The obtained output power ranges from 0.2 to 5.9 mW, depending on the pair of materials, for an active area of 46.4 cm2. The highest response was obtained for Mica with PVDF composites with 30 wt.% of barium titanate (BT) and PA66 with PU pairs. A simple application has been developed based on vertical contact-separation mode, able to power up light emission diodes (LEDs) with around 30 cycles to charge a capacitor. Further, the capacitor can be charged in one triboelectric cycle if an area of 0.14 m2 is used.This research was funded by Fundação para a Ciência e Tecnologia under framework of the Strategic Funding UID/FIS/04650/2020 and projects UIDB/05549/2020 and TSSiPRO-NORTE-01-0145-FEDER-000015. The authors also thank the F.C.T. for financial support under grants SFRH/BD/140242/2018 (T.R.M.), SFRH/BPD/98109/2013 (P.C.). Finally, the authors acknowledge funding by Spanish State Research Agency (A.E.I.) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, are also acknowledged

Evaluating the range expansion of recreational non-native fishes in Portuguese freshwaters using scientific and citizen science data.

Updating information on the distribution of recently introduced and other poorly known non-natives is essential to prevent and control their spread and better address biological invasions. Here, we combine scientific and citizen science data to update the distribution of five recently arrived (i.e., < 25 years), non-native fish species (Alburnus alburnus, Ameiurus melas, Rutilus rutilus, Sander lucioperca and Silurus glanis) and one rare, longer established (i.e., > 50 years), non-native (Esox lucius) in Portugal. These species have been increasingly targeted by recreational fishermen, thus likely expanding their distribution. Specifically, we obtained distribution maps for each species, based on data gathered through a comprehensive search for records in 1) scientific literature, 2) unpublished reports of research projects, and 3) citizen science databases. We gathered 443 valid records, of which 64% were from citizen science data, mainly provided by recreational fishermen. Data highlighted that all species have expanded their distribution in the last 20 years, with high numbers of new records for A. alburnus, S. lucioperca and S. glanis, mostly located in the Tagus, Guadiana and Douro river basins. Changes in species distributions reflected dispersal within invaded basins and colonisation of previously unoccupied drainages. Integrating citizen science with scientific data provides an effective framework to understand non-native species introduction and spread, stressing the need for increasingly encourage and engage recreational fishermen in information sharing

Motor uncoordination and neuropathology in a transgenic mouse model of Machado-Joseph disease lacking intranuclear inclusions and ataxin-3 cleavage products

Machado-Joseph disease (MJD) is a late-onset neurodegenerative disorder caused by a polyglutamine (polyQ) expansion in the ataxin-3 protein. We generated two transgenic mouse lineages expressing the expanded human ataxin-3 under the control of the CMV promoter: CMVMJD83 and CMVMJD94, carrying Q83 and Q94 stretches, respectively. Behavioral analysis revealed that the CMVMJD94 transgenic mice developed motor uncoordination, intergenerational instability of the CAG repeat and a tissue-specific increase in the somatic mosaicism of the repeat with aging. Histopathological analysis of MJD mice at early and late stages of the disease revealed neuronal atrophy and astrogliosis in several brain regions; however, we found no signs of microglial activation or neuroinflammatory response prior to the appearance of an overt phenotype. In our model, the appearance of MJD-like symptoms was also not associated with the presence of ataxin-3 cleavage products or intranuclear aggregates. We propose the transgenic CMVMJD94 mice as a useful model to study the early stages in the pathogenesis of MJD and to explore the molecular mechanisms involved in CAG repeat instability.We would like to thank to Dr. Henry Paulson for providing the anti-ataxin-3 serum, Dr. Monica Sousa for the pCMV vector and to Eng. Lucilia Goreti Pinto for technical assistance. AS-F., M.C.C., S.S. and C.B. received FCT fellowships (SFRH/BD/15910/2005; SFRH/BPD/28560/2006; PTDC/SAU-GMG/64076/2006; SFRH/BPD/20987/2004). This research was funded by Fundacao para a Ciencia e Tecnologia through projects FEDER/FCT, POCI/SAU-MMO/60412/2004, PTDC/SAU-GMG/64076/2006; and Ataxia MJD Research Project

Electrochemical characterization of imidazole-based carboxamidrazones in aqueous and organic solutions and structure-activity relationship

The search for new antibiotics is an emergent topic in the scientific community due to the appearance of pathogenic organisms multiresistant to the available drugs and therapy [1]. The worrying increase in infections caused by pathogenic fungi in immunosuppressed patients prompted the search for new antifungal agents with new mechanisms of action and less side effects [2]. The imidazole ring is a crucial scaffold for drug design due to its vital role in various biological processes [3]. Thus, imidazole-based molecules have been widely used to synthetize promising heterocyclic ligands for several drug targets. Furthermore, amidrazones are known for their high reactivity, being useful intermediates for the synthesis of compounds with a wide range of biological activities, including antimicrobial action. The amidrazone derivatives have also been applied in different areas of chemistry, specifically in the synthesis of azo molecules [4]. In a previous work, novel imidazole based 5-aminoimidazole-4-carboxamidrazones were synthesized, which exhibited great antifungal activity evaluated against three yeast species, namely Candida krusei, Candida albicans and Candida parapsilosis [5]. In this communication, the electrochemical characterization of some carboxamidrazones performed by cyclic voltammetry in two different media is compared. The effects of substituent groups in the different carboxamidrazones on the variation of oxidation potential of these compounds in aqueous and organic media were also analyzed. To find a relationship between chemical structure and activity, the minimum inhibitory concentration was correlated with their oxidation potentials. The effect of the variation of pH on the oxidation potential of substituted carboxamidrazones was also analyzed. In addition, kinetic studies of the evolution of some carboxamidrazones in aqueous media characterized by UV-Vis spectroscopy were performed and the obtained results were correlated with the electrochemical and biological data.: We thank Fundação para a Ciência e a Tecnologia (FCT) for financial support through the Chemistry Research Centre of the University of Minho (UID/QUI/00686/2020), CIIMAR (UIBD/04423/2020), UID/Multi/04546/2019, and 2C2T (UID/CTM/00264/2021). FEDER funds through Portugal 2020 Competitive Factors Operational Program (POCI), and the Portuguese Government (OE, grant number POCI-01-0247-ERDF 047124). This work was also supported under the projects MEDCOR (PTDC/CTM-TEX/1213/2020) and UID/CTM/00264/2019, the Research Center of the Portuguese Oncology Institute of Porto (project no. PI86-CI-IPOP-66-2019), and PhD grant SFRH/BD/137668/2018 and 2021.08081.B

description of the methodological approach

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TECNOLOGIA E INOVAÇÃO AO SERVIÇO DO EXERCÍCIO E SAÚDE. Exercício. Pandemia COVID-19. Tecnologia Vs. Isolamento Social

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