Fine Tuning of Electrical Transport and Dielectric Properties of Epoxy/Carbon Nanotubes Composites via Magnesium Oxide Additives

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.

Electrophysical Properties of Epoxy Composite Materials Filled with Carbon Black Nanopowder

“…Figure 1 shows that the nature of the electric field frequency and the amount of the introduced filler significantly affects the electrophysical properties of the materials. Studies show that, at a frequency of 100 Hz, the conductivity of the epoxy oligomer is 3 × 10 −9 S/cm [18] and 1 × 10 −10 S/cm [20]. In our study, the conductivity of the epoxy oligomer at a frequency of 100 Hz is 1.1 × 10 −9 S/cm.…”

“…e epoxy PCMs are formed using the following technique: heating the resin to a temperature T � 353 ± 2°K and holding at a given temperature for a time τ � 20 ± 0.1 min. CB is a hygroscopic material [18,19], and it can absorb moisture depending on the particle size, the presence of impurities, and storage conditions, which leads to the clumping (sticking) of the CB powder and complicates the introduction and dispersion in the melt of the polymer. Additionally, the drying of the powder is carried out in a laboratory muffle furnace heated to a temperature T � 383 ± 2°K and holding it at a given temperature for a time τ � 60 ± 0.1 min.…”

Relationship between Viscosity, Microstructure and Electrical Conductivity in Copolyamide Hot Melt Adhesives Containing Carbon Nanotubes

“…From Figure 4 a, it is possible to conclude that the behavior of critical frequency is correlated with the behavior of the DC conductivity, with no correlation with behavior of parameter s. A factor which is important for the frequency-dependent conductivity σ ( ω ) is the electron transport not only across the whole sample but also inside some conductive clusters, if the electron flight time τ inside the cluster is smaller than the reciprocal electromagnetic wave frequency 1/2π ω . Thus, bigger aggregates are related with smaller critical frequencies, while parameter s is related with the distribution of aggregates’ size [ 52 ] ( Figure 4 a and Table 2 ).…”

“…The dielectric permittivity of this sample is higher than the dielectric permittivity of samples MBcoPA1 and MbcoPA4. Such mismatch in the behavior of dielectric permittivity and electrical conductivity was already explained by the difference in distributions of relaxation times and distributions of agglomerate size [ 52 ]. Indeed, the distribution of agglomerate size is much broader for sample MBcoPA2 than for samples MBcoPA1 and MBcoPA4 (see Table 2 ).…”

Dielectric Relaxation in the Hybrid Epoxy/MWCNT/MnFe2O4 Composites

“…Using the above-mentioned preparation method, two separate series of MnFe 2 O 4 /MWCNT/epoxy resin hybrid composites with a fixed MWCNT-content and various MnFe 2 O 4 amounts were prepared. The first had a MWCNT content of 0.09 vol.% (just below the percolation state in corresponding monofiller composites [26]), and the following MnFe 2 O 4 concentrations: 0, 0.025, 0.05, 0.35, 0.65, 5, and 10 vol.%, while the second one had a higher MWCNT content of 0.58 vol.% (above percolation threshold) and 0, 0.025, and 0.58 vol.% of MnFe 2 O 4 . The volume concentrations were evaluated from weight concentrations considering that the density of epoxy resin was 1.16 g/cm 3 , MnFe 2 O 4 was 5.4 g/cm 3 , and MWCNT was 2 g/cm 3 .…”