High β phase content in PVDF/CoFe2O4 nanocomposites induced by DC magnetic fields

Abstract

Flexible ferroelectrics being exploited as energy harvesting and conversion materials are highly desirable for wearable and skin-mountable electronic devices. As one of the most typical ferroelectric polymers, poly(vinylidene fluoride) (PVDF) has been widely used in modern electronic systems and devices, whose ferroelectric performance relies heavily on its β phase content. In this work, to achieve high-β-phase-content PVDF, we first introduced CoFe2O4 nanoparticles into PVDF. With the incorporation of CoFe2O4 nanoparticles used as an effective polymer nucleation agent, the percentage of the β phase in the PVDF has been significantly enhanced, e.g., 84% in the nanocomposite with 5 wt. % CoFe2O4 versus only 73% in the pure PVDF. In order to further increase the β phase content in PVDF, we subsequently proposed an easily realized strategy. By applying DC magnetic fields during the solution-casting process of the PVDF/CoFe2O4 nanocomposites, a further improved β phase content as high as 95% can be achieved. The further improvement of the β phase content is attributable to the tensile stress at the CoFe2O4/PVDF interfaces created by the coupling of magnetic field and CoFe2O4 by means of the magnetostriction effect. The high β-phase content makes the PVDF/CoFe2O4 nanocomposites a promising candidate for flexible and wearable electronic device applications.