Publicação
High performance magnetoelectric nanocomposite morphologies for advanced applications
| Resumo: | The magnetoelectric (ME) effect is characterized by the variation of the electrical polarization of a material with an applied magnetic field and the variation of the magnetization of a material with an applied electric field. Single-phase materials with intrinsic ME effect are not generally used for practical applications since they typically show weak ME coupling at room temperatures. Such problem has been overcome by the development of ME composites. Strong ME effect at room temperature has been obtained, particularly in those composed by a piezoelectric and a magnetostrictive phase. In such materials, a strain is induced on the magnetostrictive phase once a magnetic field is applied to the composite. This strain is transmitted to the piezoelectric constituent, which undergoes a change in the electrical polarization. In an analogous way, the reverse effect can occur. The main objective of the thesis was the development of high performance polymer-based ME materials, that were characterized, optimized and their potential applications evaluated. Particulate ME composites were produced from materials with strong piezoelectric - poly(vinylidene fluoride) (P(VDF)) - and magnetostrictive - Cobalt iron oxide (CoFe2O4 - CFO) - responses in the form of film, membrane, fibers, and spheres. Related piezoelectric materials, such as the copolymer of P(VDF), poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and magnetic nanoparticles, such as magnetite (Fe3O4), goethite (δ-FeO(OH)) and CoFeO(OH), were also used. All developed morphologies show the presence of the ME effect. The studies on film morphology addressed the relevance of the magnetostrictive filler dispersion on ME composite response, suggesting that the use of surfactants or ultrasounds to improve the dispersion leads to the same ME response. The filler size and shape shows an important role on the ME measurements. Studies with Fe3O4 nanoparticle with sizes of 9, 30 and 50 nm within a P(VDF-TrFE) matrix show that the largest α31 = 0.97 mV.cm-1Oe-1 is obtained for the lowest nanoparticle size. The shape of the same filler was studied and the results shows that a rod shape, comparing with a spherical, nucleate the β-phase of P(VDF), due to the high interface interaction between the polymer and the filler. Anisotropic nanosheet fillers of δ-FeO(OH) and CoFeO(OH) were synthetized and evaluated for the preparation of ME composites. Thus, δ-FeO(OH) /P(VDF-TrFE) composites lead to a maximum ME response of 0.4 mV.cm-1.Oe-1, which depends on filler content, alignment state as well as on both incident magnetic field direction and magnitude. A new ME effect is proposed based on the magnetic rotation of the nanosheets inside the piezoelectric polymer matrix. New CoFeO(OH) highly magnetostrictive (λ = 507 ppm) and anisotropic nanostructures were synthesized by a coprecipitation method using a modified gas-slugs microfluidic system. CoFeO(OH) /P(VDF-TrFE) composites reveal an interfacial ME coupling strongly dependent on the angle between HDC and filler length direction, with a maximum α31 = 5.10 mV.cm-1.Oe-1. ME membranes were also produced in CFO/P(VDF-TrFE) composites. The porous morphology and ME response were evaluated. The porous composite shows piezoelectricity with an effective piezoelectric coefficient (d33) of -22 pC.N-1, a maximum magnetization of 12 emu.g-1 and a maximum ME coefficient of 9 mV.cm-1.Oe-1. ME nanofibers and microspheres of CFO/P(VDF) produced by electrospinning and electrospray technique, respectively, were studied and evaluated. The average diameter of the nanofibers is ≈325 nm, independently of filler content, and the amount of crystalline polar β-phase was strongly enhanced when compared to pure P(VDF) polymer fibers, due to the introduction of the magnetostrictive fillers. The piezoelectric response of these electroactive nanofibers was modified by an applied magnetic field, thus evidencing the ME character of the CFO/P(VDF) composites. The CFO nanoparticles content in the ME microspheres (3-7 µm diameter) reached values up to 27 wt.%, despite their concentration in the starting solution reaching values up to 70 wt.%. No relevant effect on β-phase content (≈60 %), crystallinity (40 %) and onset degradation temperature (460-465 °C) of the polymer matrix was observed. The ME microspheres show a maximum|d33|≈30 pC.N-1, leading to a ME response of ∆|d33|≈5 pC.N-1 obtained when a 220 mT DC magnetic field was applied. Its also shown that the interface between CFO and P(VDF) (0-55 %) has a strong influence on the ME response of the microspheres. The simplicity and the scalability of the processing methods used in the present work as well as the excellent ME response in a large variety of composite morphologies suggest a large application potential of the developed polymer-based ME composites in areas such as sensors and actuators and tissue engineering, among others. |
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| Autores principais: | Gonçalves, Renato Ferreira |
| Assunto: | Engenharia e Tecnologia::Engenharia dos Materiais |
| Ano: | 2017 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | português |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | The magnetoelectric (ME) effect is characterized by the variation of the electrical polarization of a material with an applied magnetic field and the variation of the magnetization of a material with an applied electric field. Single-phase materials with intrinsic ME effect are not generally used for practical applications since they typically show weak ME coupling at room temperatures. Such problem has been overcome by the development of ME composites. Strong ME effect at room temperature has been obtained, particularly in those composed by a piezoelectric and a magnetostrictive phase. In such materials, a strain is induced on the magnetostrictive phase once a magnetic field is applied to the composite. This strain is transmitted to the piezoelectric constituent, which undergoes a change in the electrical polarization. In an analogous way, the reverse effect can occur. The main objective of the thesis was the development of high performance polymer-based ME materials, that were characterized, optimized and their potential applications evaluated. Particulate ME composites were produced from materials with strong piezoelectric - poly(vinylidene fluoride) (P(VDF)) - and magnetostrictive - Cobalt iron oxide (CoFe2O4 - CFO) - responses in the form of film, membrane, fibers, and spheres. Related piezoelectric materials, such as the copolymer of P(VDF), poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), and magnetic nanoparticles, such as magnetite (Fe3O4), goethite (δ-FeO(OH)) and CoFeO(OH), were also used. All developed morphologies show the presence of the ME effect. The studies on film morphology addressed the relevance of the magnetostrictive filler dispersion on ME composite response, suggesting that the use of surfactants or ultrasounds to improve the dispersion leads to the same ME response. The filler size and shape shows an important role on the ME measurements. Studies with Fe3O4 nanoparticle with sizes of 9, 30 and 50 nm within a P(VDF-TrFE) matrix show that the largest α31 = 0.97 mV.cm-1Oe-1 is obtained for the lowest nanoparticle size. The shape of the same filler was studied and the results shows that a rod shape, comparing with a spherical, nucleate the β-phase of P(VDF), due to the high interface interaction between the polymer and the filler. Anisotropic nanosheet fillers of δ-FeO(OH) and CoFeO(OH) were synthetized and evaluated for the preparation of ME composites. Thus, δ-FeO(OH) /P(VDF-TrFE) composites lead to a maximum ME response of 0.4 mV.cm-1.Oe-1, which depends on filler content, alignment state as well as on both incident magnetic field direction and magnitude. A new ME effect is proposed based on the magnetic rotation of the nanosheets inside the piezoelectric polymer matrix. New CoFeO(OH) highly magnetostrictive (λ = 507 ppm) and anisotropic nanostructures were synthesized by a coprecipitation method using a modified gas-slugs microfluidic system. CoFeO(OH) /P(VDF-TrFE) composites reveal an interfacial ME coupling strongly dependent on the angle between HDC and filler length direction, with a maximum α31 = 5.10 mV.cm-1.Oe-1. ME membranes were also produced in CFO/P(VDF-TrFE) composites. The porous morphology and ME response were evaluated. The porous composite shows piezoelectricity with an effective piezoelectric coefficient (d33) of -22 pC.N-1, a maximum magnetization of 12 emu.g-1 and a maximum ME coefficient of 9 mV.cm-1.Oe-1. ME nanofibers and microspheres of CFO/P(VDF) produced by electrospinning and electrospray technique, respectively, were studied and evaluated. The average diameter of the nanofibers is ≈325 nm, independently of filler content, and the amount of crystalline polar β-phase was strongly enhanced when compared to pure P(VDF) polymer fibers, due to the introduction of the magnetostrictive fillers. The piezoelectric response of these electroactive nanofibers was modified by an applied magnetic field, thus evidencing the ME character of the CFO/P(VDF) composites. The CFO nanoparticles content in the ME microspheres (3-7 µm diameter) reached values up to 27 wt.%, despite their concentration in the starting solution reaching values up to 70 wt.%. No relevant effect on β-phase content (≈60 %), crystallinity (40 %) and onset degradation temperature (460-465 °C) of the polymer matrix was observed. The ME microspheres show a maximum|d33|≈30 pC.N-1, leading to a ME response of ∆|d33|≈5 pC.N-1 obtained when a 220 mT DC magnetic field was applied. Its also shown that the interface between CFO and P(VDF) (0-55 %) has a strong influence on the ME response of the microspheres. The simplicity and the scalability of the processing methods used in the present work as well as the excellent ME response in a large variety of composite morphologies suggest a large application potential of the developed polymer-based ME composites in areas such as sensors and actuators and tissue engineering, among others. |
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