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Now showing items 1 - 16 of 29

  • Stretchable scintillator composites for indirect X-ray detectors

    J. Oliveira   V. Correia   P. Costa   A. Francesko   G. Rocha   S. Lanceros-Mendez  

    Abstract Flexible and stretchable materials are increasingly being investigated for future technological platforms, polymer based materials being the most suitable candidates for those emerging technologies. This work reports on polymer based scintillator composites based on the thermoplastic elastomer Styrene-Ethylene/Butadiene-Styrene (SEBS) and Gd 2 O 3 :Eu 3+ scintillator nanoparticles, to form a polymer-based flexible and stretchable material for X-ray indirect detectors. Further, visible light yield under X-ray irradiation was improved by the inclusion of 2,5 dipheniloxazol (PPO) and (1,4-bis (2-(5-phenioxazolil))-benzol (POPOP) within the polymer matrix. Together with high levels of stretchability, with deformations up to 100%, the films exhibit suitable performance with low mechanical hysteresis (less than 1.5 MJ/m 3 for cycles up to 100% of strain) and reproducibly such as a scintillator material for the conversion of X-ray radiation into visible radiation. The decrease of just ∼13% of the X-ray radiation into visible light upon stretching up to 100% is attributed to a reduction of the effective filler concentration and proves the suitability of the developed materials for large area and stretchable X-ray radiation detectors. Graphical abstract Image 1 Highlights • Polymer-based scintillator materials have been developed based on Gd 2 O 3 :Eu 3+ nanoparticles. • The films exhibit high levels of stretchability with suitable performance. • The composites can be used for the fabrication of large area stretchable X-ray detectors.
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  • Piezoresistive polymer blends for electromechanical sensor applications

    P. Costa   J. Oliveira   Laura Horta-Romarís   María-José Abad   J. Agostinho Moreira   I. Zapiráin   M. Aguado   S. Galván   S. Lanceros-Mendez  

    Abstract Doped polyaniline (PANI) exhibits excellent electrical properties that can be used in composite materials to replace metallic or carbonaceous nanofillers commonly used in composites for sensor applications. Polymer blends based on PANI and thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) copolymer have been prepared by solvent casting showing large strain yield (>10% for 40 wt% PANI content), high electrical conductivity, 1 S/m, after the percolation threshold at ≈10 wt% PANI. Further, the composites show suitable piezoresistive response with gauge factor ( GF ) between GF  ≈ 1.5 and 2.4 for deformations up to 10%. The overall properties of the solution casted PANI/SEBS blends indicate their suitability for advanced electromechanical sensors applications, with simple integration and processable by solution printing technologies. Graphical abstract Image 1
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  • Magnetoelectric response on Terfenol-D/ P(VDF-TrFE) two-phase composites

    R. Brito-Pereira   C. Ribeiro   S. Lanceros-Mendez   P. Martins  

    Abstract Magnetoelectric (ME) particulate composites films composed of Terfenol-D (TD) particles embedded in P(VDF-TrFE) (70/30) polymer have been developed. The effect of TD content on the mechanical, dielectric, electric, magnetic, piezoelectric and ME properties was studied and discussed. It is shown that the addition of TD particles into the polymer matrix increased the Young's modulus of from 0.86 GPa from the pristine co-polymer to 0.96 GPa for the composite with 60 wt.% filler content. The dielectric characterization showed an increase of the permittivity and dielectric loss with increasing filler content, being maximized for sample with 60 wt.% of TD (13 and 0.05 respectively). The poling process optimized the d 33 piezoelectric response of the composites to ≈ -15 pC.N −1 value. The room temperature ferromagnetism (150 Oe coercivity and 8.6 emu.g −1 saturation magnetization) and high magnetoelectric voltage coupling (38 mV cm −1 .Oe −1 ), the highest reported for two phase TD polymer composites, allows the development of flexible ME devices. Graphical abstract Image 1
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  • High-temperature polymer based magnetoelectric nanocomposites

    A. Maceiras   P. Martins   R. Gonçalves   G. Botelho   E. Venkata Ramana   S.K. Mendiratta   M. San Sebastián   J.L. Vilas   S. Lanceros-Mendez   L.M. León  

    Graphical abstract Highlights • High temperature magnetoelectric polymer base composites are reported. • The nanocomposite is based on polyimides and CoFe 2 O 4 nanoparticles. • The magnetization response is determined by the CFO nanoparticle content. • The piezoelectric response of the 0CN2CN polymer matrix is ≈11 pC N −1 . • The α 33 value (0.8 mV cm −1 Oe −1 ) is stable over time and decrease above 130 °C. Abstract The use of polymer based magnetoelectric materials for sensing and actuation applications has been the subject of increasing scientific and technological interest. One of the drawbacks to be overcome in this field is to increase the temperature range of application above 100 °C. In this way, a nanocomposite material composed by a mixture of two aromatic diamines, 1,3-bis-2-cyano-3-(3 aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-bis(3-aminophenoxy)benzene (diamine 0CN) and CoFe 2 O 4 (CFO) nanoparticles was designed, fabricated and successfully tested for high temperature magnetoelectric applications. Results revealed that CFO nanoparticles are well distributed within the 0CN2CN polymer matrix and that the addition of CFO nanoparticles does not significantly alter the polyimides structure. The magnetization response of the composite is determined by the CFO nanoparticle content. The piezoelectric response of the 0CN2CN polymer matrix (≈11 pC N −1 ) and the maximum α 33 value (0.8 mV cm −1 Oe −1 ) are stable over time and decrease only when the composite is subjected to temperatures above 130 °C. Strategies to further improve the ME response are also discussed.
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  • Size effects on the magnetoelectric response on PVDF/Vitrovac 4040 laminate composites

    M.P. Silva   P. Martins   A. Lasheras   J. Gutiérrez   J.M. Barandiarán   S. Lanceros-Mendez  

    Abstract Tri-layered and bi-layered magnetoelectric (ME) flexible composite structures of varying geometries and sizes consisting on magnetostrictive Vitrovac and piezoelectric poly(vinylidene fluoride) (PVDF) layers were fabricated by direct bonding. From the ME measurements it was determined that tri-layered composites structures (magnetostrictive–piezoelectric–magnetostrictive type), show a higher ME response (75 V cm −1 Oe −1 ) than the bi-layer structure (66 V cm −1 Oe −1 ). The ME voltage coefficient decreased with increasing longitudinal size aspect ratio between PVDF and Vitrovac layers (from 1.1 to 4.3), being observed a maximum ME voltage coefficient of 66 V cm −1 Oe −1 . It was also observed that the composite with the lowest transversal aspect ratio between PVDF and Vitrovac layers resulted in better ME performance than the structures with higher transversal size aspect ratios. It was further determined an intimate relation between the A re a P V D F / A re a V it ro va c ratio and the ME response of the composites. When such ratio values approach 1, the ME response is the largest. In addition the ME output value and magnetic field response were controlled by changing the number of Vitrovac layers, which allows the development of magnetic sensors and energy harvesting devices. Graphical abstract Highlights • Vitrovac/PVDF laminates have been fabricated. • Size and aspect ratio effects on the ME response have been investigated. • Bi-layered and three-layered composites have been investigated • High ME response of 75 V cm −1 Oe −1 has been obtained. • The tailored ME response is suitable for sensor applications.
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  • Effect of cylindrical filler aggregation on the electrical conductivity of composites

    Jaime Silva   S. Lanceros-Mendez   R. Simoes  

    Abstract This work reports on the effect of carbon nanotube aggregation on the electrical conductivity and other network properties of polymer/carbon nanotube composites by modeling the carbon nanotubes as hard-core cylinders. It is shown that the conductivity decreases for increasing filler aggregation, and that this effect is more significant for higher cylinder volume fractions. It is also demonstrated, for volume fractions at which the giant component is present, that increasing the fraction of cylinders within clusters leads to a break of the giant component and the formation of a set of finite clusters. The decrease of the giant component with the increase of the fraction of cylinders within the cluster can be related to a decrease of the spanning probability due to a decrease of the number of cylinders between the clusters. Finally, it is demonstrated that the effect of aggregation can be understood by employing the network theory. Highlights • The effect of filler aggregation on the electrical conductivity of composites is studied. • It is shown that the conductivity decreases for increasing filler aggregation. • Increasing the clusters size leads to a break of the giant component. • The effect of aggregation can be understood by employing the network theory.
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  • Kinetic study of thermal degradation of chitosan as a function of deacetylation degree

    M.A. Gámiz-González   D.M. Correia   S. Lanceros-Mendez   V. Sencadas   J.L. Gómez Ribelles   A. Vidaurre  

    Highlights • Coupling of the degradation of acetylated and deacetilated units in chitosan with varying deacetylation degree. • Model fitting of degradation in overlapped degradation mechanisms. • Previous activation energy determination by applying “free model” methods allows subsequent model fitting of TGA traces. • Sestack-Berggren model yields the best fit to the experimental data in chitosan. Abstract Thermal degradation of chitosan with varying deacetylation degree (DD) ranging between 50 and 85% was analyzed by dynamic thermogravimetric analysis at different heating rates. The present study focused on the temperature range between 500 and 800 K, above water evaporation. Thermal degradation showed a main degradation stage in this temperature interval with a second stage that appeared in the weight derivative curves as a shoulder in the high temperature side of the main peak with increasing intensity as the DD decreased. The Kissinger and isoconversional Ozawa-Flynn-Wall models were employed to evaluate the Ea of both thermal degradation processes. Different kinetic models were tested to computer simulate the thermogravimetric traces calculating the model parameters with a non-linear least squares fitting routine. The Sestack-Berggren model allowed reproducing accurately the overlapping of the two degradation mechanisms and calculating the mass fraction lost in each of them revealing the coupling between the two degradation mechanisms.
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  • Development of water-based printable piezoresistive sensors for large strain applications

    B.F. Gonçalves   J. Oliveira   P. Costa   V. Correia   P. Martins   G. Botelho   S. Lanceros-Mendez  

    Abstract Polymer based smart materials and, in particular, piezoresistive ones, are increasingly being used in a wide variety of applications ranging from automotive components to medical devices. This work reports on water-based piezoresistive polymer composites developed from thermoplastic poly (vinyl alcohol) (PVA) filled with carbon nanotubes (MWCNT) for the fabrication of high performance piezoresistive materials and sensors. PVA is a water-soluble synthetic polymer with suitable mechanical properties for the development of large strain sensors. MWCNT/PVA nanocomposites with good linearity between deformation and electrical resistance variation and with gauge factors up to 3 were achieved. Further, the materials were formulated in the form of inks for spray and screen printing of the sensors, which demonstrated a good performance for strain sensing both under laboratory tests conditions and when connected to a readout and communication system. Therefore, polymer based piezoresistive sensors were developed by a green approach and capable to be implemented by scalable printing technologies. Graphical abstract Image 1 Highlights • Water-based printable piezoresistive sensors were developed. • The sensors are based on MWCNT/PVA composites. • The stretchable sensors are suitable for large strain applications. • The developed inks can be applied by screen and spray printing. • The electronic readout system with RF communication was also developed.
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  • Silk fibroin-magnetic hybrid composite electrospun fibers for tissue engineering applications

    R. Brito-Pereira   D.M. Correia   C. Ribeiro   A. Francesko   I. Etxebarria   L. Pérez-Álvarez   J.L. Vilas   P. Martins   S. Lanceros-Mendez  

    Abstract This manuscript reports on the fabrication of silk fibroin (SF)-based magnetic electrospun fiber composites as scaffolds for tissue engineering applications. The magnetic responsiveness of the SF composite fibers was achieved by the inclusion of cobalt ferrite (CoFe 2 O 4 ) or magnetite (Fe 3 O 4 ) nanoparticles prior to processing the fibers via electrospinning. The influence of the processing parameters, including type and amount of nanoparticles in the composite, on the mean fiber size and size distribution was studied. Whereas the average diameter of pristine SF fibers was of 294 ± 53 nm, the inclusion of 5% of CoFe 2 O 4 and Fe 3 O 4 nanoparticles led to a slight increase in the fiber diameter. Nevertheless, the fiber diameter decreased with the higher nanoparticles loading. Regarding the physico-chemical properties of the fibrous mats, it was observed that the degree of crystallinity dropped from 67% of the pristine SF mats to 37% for the SF composites. On the other hand, the onset degradation temperature of the SF electrospun was not significantly altered by inclusion of ferrite nanoparticles. It is shown that the magnetization saturation increased with the nanoparticle filler content for both compositions (CoFe 2 O 4 /SF and Fe 3 O 4 /SF). Neither the SF pristine fibers nor the SF composites were cytotoxic, indicating their suitability for tissue engineering applications. Graphical abstract Image 1 Highlights • Silk fibroin (SF) magnetic composite fiber mats were processed by electrospinning. • CoFe 2 O 4 and Fe 3 O 4 nanoparticles up to 20%wt content were used as magnetic fillers. • The SF and SF magnetic composite fiber mats are not cytotoxic. • The composite fibers show suitable properties for tissue engineering applications.
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  • Effect of the acoustic impedance in ultrasonic emitter transducers using digital modulations

    M.S. Martins   J. Cabral   S. Lanceros-Mendez   G. Rocha  

    Abstract The existing technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in the aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. For high data-rates and real-time applications it is necessary to use frequencies in the MHz range, allowing communication distances of hundreds of meters with a delay of milliseconds. To achieve this goal, it is necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. This work shows how the acoustic impedance influences the performance of an ultrasonic emitter transducer when digital modulations are used and operating at frequencies between 100 kHz and 1 MHz. The study includes a Finite Element Method and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based on ceramics (high acoustic impedance) with a resonance design and the other based in polymer (low acoustic impedance) designed to optimize the performance when digital modulations are used. The transducers performance for Binary Amplitude Shift Keying, On–Off Keying, Binary Phase Shift Keying and Binary Frequency Shift Keying modulations with a 1 MHz carrier at 125 kbps baud rate are compared. Highlights • Study of the acoustic impedance effect in signal quality for ultrasonic transducers using digital modulations. • Two types of transducers were tested based on PZT-5H ceramic based transducers and on PVDF polymers. • The study includes MATLAB/Simulink simulations and experimental validations for BASK, OOK, BFSK and BPSK modulations with a 1 MHz carrier at 125 kbps baud rate.
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  • Electroactive phases of poly(vinylidene fluoride): Determination, processing and applications

    P. Martins   A.C. Lopes   S. Lanceros-Mendez  

    Abstract Poly(vinylidene fluoride), PVDF, and its copolymers are the family of polymers with the highest dielectric constant and electroactive response, including piezoelectric, pyroelectric and ferroelectric effects. The electroactive properties are increasingly important in a wide range of applications such as in biomedicine, energy generation and storage, monitoring and control, and include the development of sensors and actuators, separator and filtration membranes and smart scaffolds, among others. For many of these applications the polymer should be in one of its electroactive phases. This review presents the developments and summarizes the main characteristics of the electroactive phases of PVDF and copolymers, indicates the different processing strategies as well as the way in which the phase content is identified and quantified. Additionally, recent advances in the development of electroactive composites allowing novel effects, such as magnetoelectric responses, and opening new applications areas are presented. Finally, some of the more interesting potential applications and processing challenges are discussed.
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  • High performance screen printable lithium-ion battery cathode ink based on C-LiFePO4

    R.E. Sousa   J. Oliveira   A. Gören   D. Miranda   M.M. Silva   Loic Hilliou   C.M. Costa   S. Lanceros-Mendez  

    Highlights • C-LiFePO 4 paste was been prepared for screen-printing technique. • The inks produced have a Newtonian viscosity of 3 Pa.s for this printing technique. • C-LiFePO 4 inks present a 48.2 mAh.g −1 after 50 cycles at 5C. • This ink is suitable in the development of printed lithium ion batteries. Abstract Lithium-ion battery cathodes have been fabricated by screen-printing through the development of C-LiFePO 4 inks. It is shown that shear thinning polymer solutions in N-methyl-2-pyrrolidone (NMP) with Newtonian viscosity above 0.4 Pas are the best binders for formulating a cathode paste with satisfactory film forming properties. The paste shows an elasticity of the order of 500 Pa and, after shear yielding, shows an apparent viscosity of the order of 3 Pas for shear rates corresponding to those used during screen-printing. The screen-printed cathode produced with a thickness of 26 μm shows a homogeneous distribution of the active material, conductive additive and polymer binder. The total resistance and diffusion coefficient of the cathode are ∼ 450 Ω and 2.5 × 10 −16 cm 2 s −1 , respectively. The developed cathodes show an initial discharge capacity of 48.2 mAhg −1 at 5C and a discharge value of 39.8 mAhg −1 after 50 cycles. The capacity retention of 83% represents 23% of the theoretical value (charge and/or discharge process in twenty minutes), demonstrating the good performance of the battery. Thus, the developed C-LiFePO 4 based inks allow to fabricate screen-printed cathodes suitable for printed lithium-ion batteries.
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  • High-performance graphene-based carbon nanofiller/polymer composites for piezoresistive sensor applications

    P. Costa   J. Nunes-Pereira   J. Oliveira   J. Silva   J. Agostinho Moreira   S.A.C. Carabineiro   J.G. Buijnsters   S. Lanceros-Mendez  

    Abstract Poly(vinylidene fluoride) (PVDF) composites with different carbonaceous nanofillers, prepared by solution casting, were studied their chemical, mechanical, electrical and electro-mechanical properties evaluated. Few-layer graphene (FLG) nanoplatelets (G-NPL), graphene oxide (GO) and reduced graphene oxide (rGO) and single-walled carbon nanohorns (SWCNH)) were found to have a strong influence in the overall properties of the composites prepared with up to 5 wt% nanofiller contents. The mechanical strain of carbonaceous nanofillers/PVDF composites decreases from 15% to near 5% of maximum strain. The electrical percolation threshold depends on the nanofiller type, being below 1 wt% for rGO and near 2 wt% for the remaining nanofillers. The electrical conductivity shows a maximum increase of nine orders of magnitude, from σ ≈ 5 × 10 −11 S/m of pure PVDF to σ ≈ 1 × 10 −2 S/m for rGO/PVDF composites with 5 wt% nanofillers. The conduction mechanism being related to hopping between the carbonaceous nanofillers for concentrations higher than the percolation threshold. Furthermore, the composites show electro-mechanical properties, except for G-NPL materials, with rGO/PVDF composites with 5 wt% nanofiller content showing higher Gauge factor (GF) values, reaching GF≈ 11 for deformations between 0.5 and 2 mm in 4-point bending experiments. These results demonstrate the suitability of the composites for strain sensing applications.
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  • Effect of anion type in the performance of ionic liquid/poly(vinylidene fluoride) electromechanical actuators

    R. Mejri   J.C. Dias   S. Besbes Hentati   M.S. Martins   C.M. Costa   S. Lanceros-Mendez  

    Abstract Low voltage actuators based on poly(vinylidene fluoride) (PVDF) with 10, 25 and 40% 1-hexyl-3-methylimidazolium chloride ([C 6 mim][Cl]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 6 mim][NTf 2 ]) are prepared by solvent casting in order to evaluate the effect of anion size in the bending properties. Independently of the ionic liquid type and content, its presence leads to the crystallization of PVDF in the β-phase. The addition of ionic liquid into the polymer matrix decreases significantly its degree of crystallinity and the elastic modulus. It is also confirmed the good miscibility between PVDF and IL, determined by the interaction of the CF 2 groups from the PVDF chains with the imidazolium ring in the ionic liquid (IL). The AC conductivity of the composites depends both on the amount of ionic liquid content and anion size. The bending movement of the IL/PVDF composites is correlated to their degree of crystallinity, mechanical properties and ionic conductivity value and the best value of bending response (0.53%) being found for IL/P V DF composite with 40 wt% of [C 6 mim][Cl] at an applied voltage of 10 V square signal. Highlights • Electromechanical actuators based on IL/PVDF blends were prepared. • Electromechanical actuator performance was evaluated as a function of anion type. • Actuator performance is correlated with the mechanical and electrical properties. • The best bending response is found for IL/PVDF blends with 40 wt% of [C 6 mim][Cl].
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  • Lithium ion rechargeable batteries: State of the art and future needs of microscopic theoretical models and simulations

    D. Miranda   C.M. Costa   S. Lanceros-Mendez  

    Graphical abstract Highlights • The microscopic theoretical models for battery simulations are reviewed. • The main results of the models are presented. • The main materials for electrodes and separators are presented. • The main parameters influencing battery performance are indicated. • The main needs for further developments are outlined. Abstract This review deals with the recent developments and present status of the theoretical models for the simulation of the performance of lithium ion batteries. Preceded by a description of the main materials used for each of the components of a battery -anode, cathode and separator- and how material characteristics affect battery performance, a description of the main theoretical models describing the operation and performance of a battery are presented. The influence of the most relevant parameters of the models, such as boundary conditions, geometry and material characteristics are discussed. Finally, suggestions for future work are proposed.
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  • Poly(vinylidene fluoride-trifluoroethylene)/NAY zeolite hybrid membranes as a drug release platform applied to ibuprofen release

    H. Salazar   A.C. Lima   A.C. Lopes   G. Botelho   S. Lanceros-Mendez  

    Graphical abstract Highlights • PVDF-TrFE/NaY zeolite composite membranes were evaluated as a drug release platform. • Loading and release of ibuprofen was measured. • The release profile can be described by the Korsmeyer-Peppas model. • Zeolite content allows tailoring membrane drug release content. • The drug release platform is suitable for other drugs and applications. Abstract Poly(vinylidene fluoride-trifluoroethylene)/NaY zeolite composite membranes were prepared by solvent casting and evaluated as a suitable drug release platform through the evaluation of loading and release of ibuprofen. The membranes were characterized at the morphological, structural and mechanical levels. The 1 H NMR spectra indicate that only the membranes with 16 and 32% of NaY were useful for IBU encapsulation and the drug release was followed by UV–vis spectroscopy. The release profile is independent of the zeolite content and can be described by the Korsmeyer-Peppas model. The membrane with 32% zeolite content releases more than double IBU amount when compared with the membrane with 16% showing that zeolite content allows tailoring membrane drug release content for specific applications. The drug release platform developed in this work is suitable for other drugs and applications.
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