Carbon Nanotube-Epoxy Nanocomposites: Correlation and Integration of Dynamic Impedance, Dielectric, and Mechanical Analyses

O Moudam,J F Watts,G Reed,T Andrews,C Lekakou

doi:10.1155/2013/801850

Abstract

This study focuses on the characterization of MWNT-epoxy composites for different MWNT concentrations of 0–7 wt% by correlating different dynamic analysis techniques, including DMA, impedance, and DEA. An optimum composition was established at 0.1 wt% MWNTs corresponding to the best MWNT dispersion which resulted in the formation of an optimum MWNT network. The addition of this low fraction of MWNTs in epoxy resulted in stiffening the molecular structure and suppressing certain molecular transitions, raising the dielectric constant especially in the low-to-medium frequency range, raising the electrical conductivity especially at the high frequencies, and increasing the electromagnetic shielding effectiveness. The 0.1% MWNT-epoxy nanocomposite switched the electromagnetic shielding behaviour from being a very effective absorber at low frequencies to being an effective reflector at high frequencies. Finally, the Nyquist plot derived from the dynamic impedance spectroscopy proved most useful at providing evidence of multiple size distribution of MWNT agglomerates.

Highlights

Epoxy resin is the polymer matrix used most often with reinforcing fibres for advanced composite applications and is widely employed as an insulation material in many electrical and electronic applications because of its excellent electrical and mechanical characteristics [1,2,3,4,5]
The Dynamic mechanical analysis (DMA) results indicate a transition starting at 63 Hz, common to both pure epoxy and multiwall carbon nanotubes (MWNTs)-epoxy nanocomposite
Pure epoxy seems to have another transition peak at 31.5 Hz, which seems to have been suppressed in the MWNT-epoxy nanocomposite, most probably because the carbon nanotubes (CNTs) network stiffens the material and inhibits further molecular transition at 31.5 Hz

Summary

Introduction

Epoxy resin is the polymer matrix used most often with reinforcing fibres for advanced composite applications and is widely employed as an insulation material in many electrical and electronic applications because of its excellent electrical and mechanical characteristics [1,2,3,4,5]. CNTs possess excellent electrical and mechanical [12,13,14,15], thermal [16], and magnetic properties [17] and chemical stability Most their nanocomposites with a high surface area of the CNT network are of low density, high strength, improved toughness, and electrically conductive [18]. Various physical and chemical methodologies have been proposed to disentangle CNTs by wrapping them with long polymer chains of polymer additives or surfactants or by functionalizing them with groups with long organic tails that wrap around the nanotubes Such methods are very effective at dispersing the CNTs, the wrapping organic chains act as insulators at the CNT-CNT contacts and reduce the electrical and thermal conductivity of the network so that the resulting nanocomposite may have improved mechanical properties but low electrical and thermal conductivity [38]. The effectiveness of the electromagnetic shielding of these materials was estimated over the tested frequency range

Materials and Experimental Techniques

Results

Conclusions