Development and characterization of multifunctional yttrium iron garnet/epoxy nanodielectrics

Abstract

In the present work, a series of yttrium iron garnet/epoxy nanocomposite systems were fabricated, and the morphology of nanocomposites were tested by Scanning Electron Microscopy. The thermal stability of the developed systems was assessed by Thermogravimetric Analysis; their thermal properties were further investigated via Differential Scanning Calorimetry (DSC) and their viscoelastic response via Dynamic Mechanical Analysis (DMA). Finally, the dielectric characterization was carried out by means of Broadband Dielectric Spectroscopy. DSC curves revealed an endothermic step-like transition of all systems, attributed to the glass to rubber transition of the polymer matrix. All nanocomposites exhibit a two stages degradation profile. The presence of nanoinclusions enhances the thermal stability of the systems shifting the onset of the first degradation process to higher temperatures. Through the DSC and DMA techniques, the transition from glassy to rubbery state of the polymer matrix was observed and the characteristic Tg temperature was determined. The addition of the ceramic inclusions enhances the thermomechanical properties, as well as the dielectric response of the nanocomposites, as implied by the augmenting values of the real part of dielectric permittivity along with the storage modulus with the reinforcing phase loading. Three dielectric relaxation processes were identified: interfacial polarization, glass to rubber transition of the polymer matrix and reorientation of the small polar side groups of the polymer chain at low, intermediate and high frequencies, respectively. Furthermore, the ability of the systems to store energy was examined via the dielectric reinforcing function.