Abstract
The dielectric properties of epoxy/MWCNT (multi-walled carbon nanotubes)/MgO hybrid composites with a fixed MWCNT amount of 0.12 vol.% (0.2 wt.%) and varying MgO concentrations up to 3 vol.% were investigated in broad frequency (20–40 GHz) and temperature (20–500 K) ranges. The composites with up to 2 vol.% MgO nanoparticles concentration showed a significant increase of DC conductivity in relation to their non MgO-containing counterparts. The optimal content of MgO was found, i.e., 0.46 vol.%, which gave up to 2.5 orders of magnitude larger DC conductivity than those of the samples prepared without MgO additives. Using various amounts of MgO, it is possible to predictably vary the broadband electromagnetic properties of the composites, even entirely eliminating the electrical percolation. Electrical transport at different temperatures can be substantially controlled by the addition of given amounts of MgO. The broadband properties are discussed in terms of the distribution of relaxation times, which are proven to be an effective, noninvasive, and simple tool for checking composite fabrication issues, such as the distribution of MWCNT aggregates within the epoxy matrix.
Highlights
Multifunctional composites are becoming ever more common and essential in modern industrial and commercial applications due to their being lightweight, flexible, and electrically conductive polymers for electromagnetic coatings
Carbon nanotubes (CNTs) [3] have been identified as a suitable filler for composites owing to their unique thermal, electrical, mechanical properties, and especially because of their extremely high length:diameter ratio [1]
The dielectric properties of epoxy/multi-walled CNTs (MWCNTs)/MgO hybrid composites with a fixed MWCNTs amount of 0.12 vol.% and varying MgO concentrations up to 3 vol.% were investigated over broad frequency and temperature ranges
Summary
Multifunctional composites are becoming ever more common and essential in modern industrial and commercial applications due to their being lightweight, flexible, and electrically conductive polymers for electromagnetic coatings. If an insulating polymer matrix is filled with a sufficient concentration of electrically conductive particles, the electrical percolation effect occurs, raising the conductivity sharply. It is desirable that the concentration at which the percolation appears is as low as possible, since this makes the composite less expensive and the overall mechanical performance better [1,2]. Reported percolation thresholds for composites containing randomly distributed multi-walled CNTs (MWCNTs) in an epoxy resin matrix are between 0.01 wt.%–1 wt.%, depending on the preparation method, diameter, and the quality. The huge surface area of the CNTs creates strong Van der Walls interactions between individual particles. During the preparation of CNT/polymer composites, due to the Van der Walls interactions, CNTs form extensive close-packed aggregates inside a low viscosity polymer matrix.
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