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- High deformation multifunctional composites: materials, processes, and applicationsPublication . Costa, Pedro; Nunes-Pereira, João; Rial Tubio, Carmen; Dios, Jose Ramón; Lanceros-Mendez, SenentxuStructural health monitoring (SHM) is a nondestructive process of collecting and analyzing data from structures to evaluate their conditions and predict the remaining lifetime. Multifunctional sensors are increasingly used in smart structures to self-sense and monitor the damages through the measurements of electrical resistivity of composite materials. Polymer-based sensors possess exceptional properties for SHM applications, such as low cost and simple processing, durability, flexibility, and excellent piezoresistive sensitivity. Thermoplastics, thermoplastic elastomers, and elastomer matrices can be combined with conductive nanofillers to develop piezoresistive sensors. Polymer, reinforcement fillers, processing and design have critical influences in the overall properties of the composite sensors. Together with the properties of the functional composites, environmental concerns are being increasingly relevant for applications, involving advances in materials selection and manufacturing technologies. In this scenario, additive manufacturing is playing an increasing role in modern technological solutions. Stretchable multifunctional composites applications include piezoresistive, dielectric elastomers (mainly for actuators), thermoelectric or magnetorheological materials. In the following sections, piezoresistive materials and applications will be mainly addressed based on their increasing implementation into applications.
- Effect of Polymer Dissolution Temperature and Conditioning Time on the Morphological and Physicochemical Characteristics of Poly(Vinylidene Fluoride) Membranes Prepared by Non-Solvent Induced Phase SeparationPublication . Cardoso, V. F.; Botelho, Gabriela; Morão, António; Nunes-Pereira, João; Lanceros-Mendez, SenentxuThis work reports on the production of poly(vinylidene fluoride) (PVDF) membranes by non-solvent induced phase separation (NIPS) using N,N-dimethylformamide (DMF) as solvent and water as non-solvent. The influence of the processing conditions in the morphology, surface characteristics, structure, thermal and mechanical properties were evaluated for polymer dissolution temperatures between 25 and 150 C and conditioning time between 0 and 10 min. Finger-like pore morphology was obtained for all membranes and increasing the polymer dissolution temperature led to an increase in the average pore size ( 0.9 and 2.1 m), porosity ( 50 to 90%) and water contact angle (up to 80 ), in turn decreasing the PVDF content ( 67 to 20%) with the degree of crystallinity remaining approximately constant ( 56%). The conditioning time did not significantly affect the polymer properties studied. Thus, the control of NIPS parameters proved to be suitable for tailoring PVDF membrane properties.
- Mesoporous poly(vinylidene fluoride-co-trifluoroethylene) membranes for lithium-ion battery separatorsPublication . Costa, C. M.; Kundu, Manab; Dias, J. C.; Nunes-Pereira, João; Botelho, Gabriela; Silva, M. M.; Lanceros-Mendez, SenentxuMesoporous separator membranes based on poly(vinylidene fluoride-co-trifluoroethylene), PVDF-TrFE, were prepared through the removal of ZnO nanoparticles from the polymer matrix composite. Different filler concentrations were used, and the evaluation of the morphology, mechanical properties, uptake and ionic conductivity of the membranes were demonstrated that they depend on initial ZnO content in the composite. On the other hand, the vibration peaks characteristics of PVDF-TrFE and the thermal properties are independent on initial filler content. The membrane with the best ionic conductivity, 1.6 mS/cm, is the one prepared after 70 wt.% ZnO removal. The separator membranes were assembled in Li/C-LiFePO4 half-cells exhibiting good rate capability and cycling performance, the best battery performance being obtained for the PVDF-TrFE after 70 wt.% ZnO removal. The good performance of the developed separators was also demonstrated in full battery cells. Thus, a way to tailor membrane mesoporosity is presented and it is shown that the obtained membranes represent suitable separators for lithium-ion battery applications.
- Dielectric barrier discharge plasma actuators based on thermosetting composites for flow control in wind turbines bladesPublication . Nunes-Pereira, João; Rodrigues, Frederico; Abdollahzadehsangroudi, Mohammadmahdi; Pina dos Santos, Paulo Sérgio; Silva, Marco; Pereira Silva, A; Pascoa, Jose; Lanceros-Mendez, SenentxuThe massive use of fibre reinforced plastics (FRP) in several industrial sectors such as aeronautics, aerospace, or wind turbines, raises serious environmental concerns with respect to the end-of-life of these structures, based on their poor recyclability. The low density of FRP gives it outstanding specific properties, such as strength and stiffness, when compared to materials with high recyclability rates, such as metals1. FRP find several applications in structures in which the aerodynamic performance is of extreme importance to guarantee a proper operation. In this sense, to endow these structures with the ability to control or modulate the flow around their surface could be an extraordinary feature to improve the performance of the structure, thus saving considerable amounts of energy and increasing its useful life cycle, contributing in this sense also to reduce the environmental impact of the materials. This work is focused on the development of dielectric barrier discharge (DBD) plasma actuators supported on fibre reinforced thermosetting composites, which can be used in manufacturing of wind turbine blades: epoxy resin and glass, aramid (Fig. 1) and natural flax fibres. DBD plasma actuators are electrohydrodynamic devices capable of generating induced flows of a few m/s through nonthermal plasma, that can be successfully leveraged for flow control applications2, 3. The characterization of the system was carried out in terms of mechanical (flexural strength, strain and stiffness), electrical (power consumption, capacitance, charge-discharge cycles) and electromechanical (induced flow velocity, electromechanical power and efficiency) properties. The results showed the multifunctionality of the composites, demonstrating their suitability for the application, in particular, the epoxy/glass composite with a bending stress of ≈600 MPa, which obtained an induced flow velocity of ≈2.1 m/s with a power consumption of ≈15.1 W, when powered by an AC signal of 11 kVpp and 24 kHz.
- Multifunctional Ceramics for Aeronautical and Aerospace ApplicationsPublication . Shvydyuk, Kateryna; Nunes-Pereira, João; Rodrigues, Frederico; Pascoa, Jose; Lanceros-Mendez, Senentxu; Pereira Silva, AIn the areas of aeronautics and aerospace, ceramic composites play an essential and increasing role due to their superior performance and tailorable properties, exhibiting highly specialized mechanical, thermal, and electric features1. Their main applications include thermal protection systems (TPS), thermal barrier coatings (TBC), and dielectric barrier discharge (DBD) plasma actuators, both for instrumentation and control purposes2. This work reports the manufacture and characterization of three ceramic composites capable of fulfilling the multifunctional ceramic condition according to the aforementioned applications. Accordingly, MgO-Al2O3 (MA), MgOCaZrO3 (MCZ), and Y2O3 stabilized ZrO2 (YSZ) are introduced for TPS, TBC, and DBD dielectric elements. To this aim, MA, MCZ, and YSZ ceramic composites were fabricated via a sequential process, encompassing the selection of raw powders and milling, die pressing, and sintering. Further, the samples were polished for surface optimization. Overall, the results obtained, including mechanical (Young’s and shear moduli, flexural strength, hardness, and fracture toughness), thermal (thermal conductivity and thermal expansion (CTE)), and electrical (dielectric constant) properties, report evidence that the developed ceramics show suitable multifunctional characteristics and therefore fulfil the aeronautical and aerospace demands for increased materials performances. The combined analysis of the Young’s and shear moduli (Fig.1a) with the CTE – the latter over a wide range of temperatures (Fig. 1b) – allows concluding that the cost-effective and widely used alumina appears suitable for bulk monolithic (TPS) and joint applications (TPS, TBC, and DBD).
- Piezoelectric Energy ProductionPublication . Nunes-Pereira, João; Costa, Pedro; Lanceros-Mendez, SenentxuThe concept of piezoelectric energy production is based on energy-harvesting devices using generation materials such as single crystals, ceramics, polymers, and composites. These production systems can harvest wasted environmental energy and convert it essentially into electrical energy. There are different nano- and microscale power harvesters which are increasingly useful for powering mobile electronics and low-power devices, even in hardly accessible areas. Despite many efforts in the development of new materials, the most widely used materials in device applications remain the ceramics of the lead zirconate titanate family, since they still present the higher output performances in the range of milliwatts of generated power.
- Antimicrobial and Antibiofilm Properties of Fluorinated Polymers with Embedded Functionalized NanodiamondsPublication . Nunes-Pereira, João; Costa, Pedro; Fernandes, Liliana; Carvalho, Estela O.; Fernandes, Margarida M.; Carabineiro, S.A.C.; Buijnsters, Josephus; Rial Tubio, Carmen; Lanceros-Mendez, SenentxuEnvironmentally resilient antimicrobial coatings are becoming increasingly required for a wide range of applications. For this purpose, nanocomposite thin films of poly(vinylidene fluoride) (PVDF) filled with several types of functionalized nanodiamonds (NDs) were processed by solvent casting. The effects of ND inclusion and functionalization in their morphological, structural, optical, thermal, and electrical properties were evaluated taking into account the type of the nanofiller and a concentration up to 2 wt %. The morphology, structure, and thermal features of the polymer matrix are governed by the processing conditions, and no noticeable changes occurred due to the presence of the ND fillers. The polymer crystallized mainly in the α phase with a crystallinity of ≈60%. In turn, the optical transmittance from 200 to 800 nm and the dielectric constant effectively depended on the ND type and content. The inclusion of the ND particles effectively provided antimicrobial properties to the films, which depended on the ND functionalization. This study thus shows that the incorporation of functionalized NDs into PVDF allows the development of antimicrobial coatings with tailorable optical and dielectric properties, which could be of great importance to face nowadays pandemic crisis scenario.
- Long-lasting ceramic composites for surface dielectric barrier discharge plasma actuatorsPublication . Shvydyuk, Kateryna; Rodrigues, F.F.; Nunes-Pereira, João; Pascoa, José; Lanceros-Mendez, Senentxu; Silva, A PereiraThe developed research presents a novel experimental study of the cost-effective MgO-Al2O3, MgO-CaZrO3 perovskite, and thermally stable YSZ ceramic composites for DBD plasma actuators in aerospace applications. This study focuses on the implementation of ceramic DBD plasma actuators for aerodynamic flow control and ice creation mitigation. For this purpose, electrical power consumption analysis, induced flow velocities assessment, and mechanical and thermal characterization were performed. MgO-Al2O3 presented higher induced velocities than its zirconia-based counterparts of up to 3.3 m/s, and lower heat dissipation, achieving a ceiling temperature of 46 ºC, being thereby the best-suited candidate for active flow control mechanisms. In contrast, YSZ had very high-power consumption translated into a maximum surface temperature of 155.4 ºC, establishing itself for ice mitigation. This extensive research evinces that the strategic combination of the developed ceramics’ thermomechanical, thermoelectric, and electromechanical properties allows them to be a promising breakthrough material for DBD plasma actuators.
- Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow controlPublication . Nunes-Pereira, João; Rodrigues, Frederico Miguel Freire; Abdollahzadehsangroudi, Mohammadmahdi; Pascoa, José; Lanceros-Mendez, SenentxuDielectric barrier discharge (DBD) plasma actuators are simple electrohydrodynamic devices, which are able to provide effective aerodynamic control. One of the main components of these devices is the thin dielectric layer, which allows to separate and prevent the arc between the high-voltage electrodes. Different materials can be used as dielectric layer to reduce the power consumption or boost the flow controlling effect of the actuators. In this context, this report presents a comparative study of two commercial polyimides, Kapton and Cirlex, used as dielectric layer of surface DBD plasma actuators. The electrical, dielectric, mechanical, electromechanical, and thermal properties were obtained to evaluate overall performance. It was verified that Cirlex (8.3 W) consumes less power than Kapton (21.3 W) to generate higher induced flow velocity of ≈3.4 m/s for an input voltage of 11 kVpp and 24 kHz. During one AC cycle at 11 kVpp the charge transferred for Cirlex (70 nC) is lower than for Kapton (100 nC), as well as the dielectric breakdown voltage to ignite the plasma discharge, 1.5 and 2.2 kVpp, respectively. The Cirlex DBD presents a higher voltage operation limit (at least 14 kVpp) and a more regular plasma discharge, which results in a more homogenous thermal profile and temperature distribution during its operation. The Cirlex actuator delivered higher mechanical power (6.2 mW) and achieved higher electromechanical efficiency (0.004%). The polyimide Cirlex proved to be a suitable alternative for Kapton to fabricate DBD plasma actuators for flow control with improved performance.
- Evaluation of the Physicochemical Properties and Active Response of Piezoelectric Poly(vinylidene fluoride-co-trifluoroethylene) as a Function of Its MicrostructurePublication . Gonçalves, R.; Cardoso, V. F.; Pereira, Nelson; Oliveira, Juliana; Nunes-Pereira, João; Costa, C. M.; Lanceros-Mendez, SenentxuPoly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), microstructures have been produced using different solvents, including green ones, by different techniques, such as solvent casting, screen-printing, replica molding, electrospray, and electrospinning. The obtained microstructures span from simple porous and dense films to spheres, fibers, and patterned three-dimensional architectures, with no significant variation in their physicochemical and electrical properties. The simplicity, low cost, and reproducibility of the processing techniques allied to their versatility to adapt to other materials to produce controlled and tailored microstructures with specific properties demonstrate their potential in a wide range of technological applications, including biomedical, energy storage, sensors and actuators, and filtration.