Magnetic and high-dielectric-constant nanoparticle polymer tri-composites for sensor applications

Multifunctional composites can be achieved by adding two different fillers with complementary properties to a polymer matrix. In this work, novel tri-composite multifunctional materials based on the incorporation of dielectric BaTiO3 (BT) and magnetic CoFe2O4 (CFO) nanoparticles into poly(vinylidene-fluoride) (PVDF) have been developed with enhanced dielectric and magnetic responses for applications in areas such as energy harvesting, sensors and actuators. The microstructure, polymer phases as well as the thermal stability of the samples were investigated, showing the independence of the polymer crystallization phases, degree of crystallinity and melting temperature on filler type and contents. Further, independently of the type of the filler, its content improves the degradation temperature of the tri-composites. The magnetic properties and electrical conductivity of the tri-composites are correlated with the increase in the content of the CFO filler, while the dielectric response is mainly determined by the interfacial polarization. A high dielectric constant of 26 at 1 kHz and a magnetization of 5.7 emu* g -1 are obtained for a sample of 10wt.% CFO-10wt. % BT/PVDF, which was used for the demonstration of the suitability of the materials for magnetic deformation sensing. This work provides pathways for the development of tri-composites based on PVDF with high dielectric constant and magnetic properties for application is areas such as sensors and actuators.The authors thank the FCT (Fundacao para a Ciencia e Tecnologia) for financial support under the framework of Strategic Funding Grants UID/FIS/04650/2019, UID/EEA/04436/2019 and UID/QUI/0686/2016; also, to the project PTDC/BTM-MAT/28237/2017; PTDC/EMD-EMD/28159/2017; and PTDC/FIS-MAC/28157/2017 funded by national funds through FCT and by the ERDF through the COMPETE2020 -Programa Operacional Competitividade e Internacionalizacao (POCI). The authors also thank the FCT for financial support under Grants SFRH/BD/131729/2017 (N.P.) and SFRH/BPD/112547/2015 (C.M.C.). The authors thank funding by the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/htt ps://doi.org/10.13039/501100011033 and from the Basque Government under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06)