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Concept de composites magnétoélectriques hybrides base polymère : piézoélectricité organique-inorganique et couplage magnétique

Abstract : The aim of this research is the elaboration and analysis of hybrid magnetoelectric polymer-based composite. Two different types of composites have been studied: Firstly, a two-phase system with an electroactive matrix (P(VDF-TrFE)) and magnetic particles (Ni); secondly, a system based on a nonelectroactive matrix (α-PVDF), piezoelectric particles (NaNbO3) and magnetic particles (Ni). The influence of Ni particles aspect ratio has been carefully studied. An original process of mild polyol reduction under low static magnetic field has been proposed in order to generate magnetic growth of nickel nanochains (NNCs). Electrical percolation threshold has been determined at 2.3 vol % for the NNCs. This value allows us to determine the maximum fraction of nickel in composites in order to remain insulating. Thus, the composites may be polarized and then they can exhibit piezoelectric properties. Piezoelectric coefficient d33 shows significant values up to 5.8 pC N-1 for the P(VDFTrFE)/Ni composite and 4.5 pCN-1 for the α-PVDF/NaNbO3/Ni composite. In both cases, high aspect ratio nickel particles leads to a decrease of d33 due the stiffening of the matrix. Magnetic properties such as remnant magnetization and coercive field are improved with particles aspect ratio as compared to spherical particles. This enhancement appears more clearly when composites are processed thanks to the particles orientation due to the fabrication process. Coupling ME properties have been measured for both types of composites which exhibit a strong ME response. In P(VDF-TrFE) based composite, the highest coupling (αME =4.2Vm-1Oe-1 ) is obtained with high aspect ratio nickel nanowires (250). The αME reaches up to 4.7Vm-1Oe-1 in the three-phase composite and the best coupling is measured with NiNPs. The obtained values are of the same order of magnitude for both composites. The specific interest of the three-phase composite is to allow the use of higher temperatures.
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Submitted on : Friday, September 4, 2020 - 11:39:38 AM
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Baptiste Martin. Concept de composites magnétoélectriques hybrides base polymère : piézoélectricité organique-inorganique et couplage magnétique. Electromagnétisme. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30245⟩. ⟨tel-02930218⟩

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