Dielectric Relaxation in the Hybrid Epoxy/MWCNT/MnFe2O4 Composites.

Darya Meisak,Jan Macutkevic,Polina Kuzhir,Juras Banys,Algirdas Selskis,Artyom Plyushch

doi:10.3390/polym12030697

Abstract

The electrical properties of epoxy/MWCNT (multi-walled carbon nanotubes)/MnFe2O4 hybrid composites loaded with MWCNTs (below, 0.09 vol.%, and above, 0.58 vol.%, percolation threshold) and varying concentrations of MnFe2O4 up to 10 vol.% were studied in a wide frequency range (20 Hz–40 GHz) at different temperatures (20 K–500 K). At low frequencies, the dielectric permittivity and the electrical conductivity of composites with fixed amounts of MWCNT are strongly dependent on MnFe2O4 content. For MWCNT concentrations above the percolation threshold (i.e., 0.58 vol.%), the electrical conductivity highly decreases with the increase of the MnFe2O4 fraction. In contrast, for the epoxy/MWCNT just below the onset of electrical conductivity (0.09 vol.% of MWCNTs), there exists an optimal concentration of MnFe2O4 inclusions (i.e., 0.025 vol.%), leading to a dramatic increase of the electrical conductivity by three orders of magnitude. The electrical transport in composites is mainly governed by electron tunneling at lower temperatures (below 200 K), and it is highly impacted by the matrix conductivity at higher temperatures (above 400 K). The electrical properties were discussed in terms of the Maxwell–Wagner relaxation and distributions of relaxation times. A non-invasive platform based on dielectric relaxation spectroscopy was proposed for enhancing the synergetic effect coursed by using multiple nanoinclusions in polymer composites just below the percolation threshold.

Highlights

Polymer composites with nanoinclusions are among the most prospective materials for investigations and applications due to the possibility of controlling and improving the macroscopic properties of polymers by the addition of a small amount of nanoparticles [1]
The aim of this work was to find the synergy between MnFe2 O4 nanoparticles and multi-walled carbon nanotubes (MWCNTs), if any, in the electrical properties of epoxy resin composites in a wide frequency range
It can be concluded that the best distribution of MWCNTs was observed for composites with the lowest concentration that the best distribution of MWCNTs was observed for composites with the lowest concentration of of MnFe2 O4 (0.025 vol.%)

Summary

Introduction

Polymer composites with nanoinclusions are among the most prospective materials for investigations and applications due to the possibility of controlling and improving the macroscopic properties of polymers by the addition of a small amount of nanoparticles [1]. For the electrical properties of composites composed of conducting inclusions and an insulating matrix, the electrical percolation threshold (critical concentration) is the most important parameter [4]. At this concentration, a sharp insulator-conductor transition occurs. The most promising additives for polymer composites are carbon based nanoparticles: carbon nanotubes (CNTs), graphene, and carbon black [4,5,6]. Composites with these inclusions exhibit improved conductive, dielectric, thermal, mechanical properties and low percolation threshold values [6,7,8]. Composites with other nanoinclusions, for example, ferromagnetic and ferroelectric ones, have attracted the Polymers 2020, 12, 697; doi:10.3390/polym12030697 www.mdpi.com/journal/polymers

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