Abstract
The interphase area appears to have a great impact on nanocomposite (NC) dielectric properties. However, the underlying mechanisms are still poorly understood, mainly because the interphase properties remain unknown. This is even more true if the temperature increases. In this study, a multiscale characterization of polyimide/silicon nitride (PI/Si3N4) NC dielectric properties is performed at various temperatures. Using a nanomechanical characterization approach, the interphase width was estimated to be 30 ± 2 nm and 42 ± 3 nm for untreated and silane-treated nanoparticles, respectively. At room temperature, the interphase dielectric permittivity is lower than that of the matrix. It increases with the temperature, and at 150 °C, the interphase and matrix permittivities reach the same value. At the macroscale, an improvement of the dielectric breakdown is observed at high temperature (by a factor of 2 at 300 °C) for NC compared to neat PI. The comparison between nano- and macro-scale measurements leads to the understanding of a strong correlation between interphase properties and NC ones. Indeed, the NC macroscopic dielectric permittivity is well reproduced from nanoscale permittivity results using mixing laws. Finally, a strong correlation between the interphase dielectric permittivity and NC breakdown strength is observed.
Highlights
Polymer dielectric materials are commonly used in advanced electronic devices and electric power systems’ insulation
NCs at an Macroscale temperatures higher than 100 °C for different frequencies (Figure 2a). This relaxation pheFor the PI sample, an increase of the relative dielectric permittivity is observed at nomenon is usually attributed the electrode’s polarization space charge accumu◦ C for to temperatures higher than 100 different frequencies
At 300 ◦ C the breakdown strength is improved by a factor nomenon could be related to the “Thermal stabilization effect” hypothesis introduced by of 2 compared to PI
Summary
Polymer dielectric materials are commonly used in advanced electronic devices and electric power systems’ insulation. PI-based NCs, with a small amount of nanofillers, exhibit improved mechanical, thermal [9,10,11], and dielectric properties at high temperature, as the limitation of space charge accumulation [12,13], the improvement of breakdown strength [12,14,15] and/or energy density [3,15,16] compared to the neat PI. Different models have been proposed to describe the interphase morphology and structure [17,18,19,20] In addition to these theoretical approaches, some authors have proposed to extract the interphase properties from macroscale experimental characterization methods [21,22,23,24]. To characterize interphase properties at the local scale, techniques derived from the Atomic Force Microscopy (AFM) were used: the Peak Force Quantitative NanoMechanical (PF-QNM) mode for the interphase mechanical properties and dimension determination [25,26], the Electrostatic
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