4.7 Article

Dielectric Relaxation Spectroscopy and Synergy Effects in Epoxy/MWCNT/Ni@C Composites

期刊

NANOMATERIALS
卷 11, 期 2, 页码 -

出版社

MDPI
DOI: 10.3390/nano11020555

关键词

carbon nanotubes; carbon-coated Ni; epoxy; electrical properties; conductivity; relaxation time

资金

  1. NATO SPS [G5697]
  2. H2020 RISE project [734164]
  3. Academy of Finland [320166, 334370]
  4. Horizon 2020 IF TURANDOT [836816]

向作者/读者索取更多资源

The dielectric and electric properties of Ni@C/epoxy composites and Ni@C/MWCNTs/epoxy composites were investigated over a wide frequency and temperature range. The addition of Ni@C nanoparticles can enhance the dielectric permittivity and electrical conductivity of the composites, but within a certain concentration range. Furthermore, in hybrid composites, the synergy effects of Ni@C and MWCNTs can significantly enhance the conductivity.
The dielectric/electric properties of the Ni@C (carbon-coated Ni)/epoxy composites and Ni@C/MWCNTs (multi-walled carbon nanotubes)/epoxy composites loaded with fixed MWCNTs amount just below the percolation threshold (0.09 vol.%) and Ni@C at different concentrations up to 1 vol.% were investigated in broad frequency (20 Hz-40 GHz) and temperature (30 K-500 K) regions. In composites with the only Ni@C nanoparticles, the electrical percolation threshold was determined between 10 and 15 vol.%. Above the percolation threshold the dielectric permittivity (epsilon') and the electrical conductivity (sigma) of the composites loaded with Ni@C only are high enough, i.e., epsilon' = 10(5) and sigma = 0.6 S/m at 100 Hz for composites with 30 vol.% Ni@C, to be used for electromagnetic shielding applications. The annealing to 500 K was proved to be an effective and simple tool to decrease the percolation threshold in epoxy/Ni@C composites. For hybrid composites series an optimal concentration of Ni@C (0.2 vol.%) was determined, leading to the conductivity absolute values several orders of magnitude higher than that of a composite filled with MWCNTs only. The synergy effects of using both fillers have been discussed. Below room temperature the electrical transport is mainly governed by epoxy resin compression in all composites, while the electron tunnelling was observed only in hybrid composites below 200 K. At higher temperatures (above 400 K), in addition to the nanoparticles redistribution effects, the electrical conductivity of epoxy resin makes a significant contribution to the total composite conductivity. The dielectric relaxation spectroscopy allows estimating the nanoparticles distributions in polymer matrix and could be used as the non-destructive and fast alternate to microscopy techniques for general polymer composite fabrication control.

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