Graded-permittivity polymer nanocomposites as superior dielectrics
Materials exhibiting a gradient in permittivity are synthesized through the application of an external magnetic field to a suspension of Fe3O4@TiO2 nanoparticles in an epoxy matrix. It is shown how the application of the magnetic field not only induces the magnetophoretic motion of the particles, but causes also their alignment in high aspect ratio structures. The combination of these two effects gives rise to graded nanocomposites exhibiting gradients in permittivity that go beyond the ones predicted for nanocomposites with homogeneously distributed and isotropic inclusions. Moreover, it is demonstrated through numerical simulations how such nanocomposites, employed as electrical insulators, can efficiently reduce the electrical field stress at the interface between the electrode and the insulator, being therefore suitable candidates as long-lasting high-voltage dielectrics. (C) 2016 Elsevier Ltd. All rights reserved.