Tailored alignment of functionalized multiwall carbon nanotubes in epoxy

The objective of this paper is to investigate the effect of frequency and strength of electric fields applied during processing on the alignment of functionalized multiwall carbon nanotubes (MWCNTs) in epoxy. The degree of alignment is assessed based on the electrical resistance parallel and transverse to the direction of field. The strengths of electric fields used for alignment were 100 and 300 V/cm and the frequencies at which these electric fields were applied ranged from 100-100k Hz. The MWCNTs had either covalent (amine) or non-covalent functionalization and were added to the epoxy at 0.5 wt% concentration. For noncovalently functionalized MWCNTs, the DC electrical resistivity was found to be sensitive to the nature of the field applied during processing. In comparison to no applied field, the parallel DC resistivity decreased and the transverse DC resistivity varied versus frequency, with a peak in electrical anisotropy observed at a 100 Hz alignment frequency. The main source of the variation of anisotropy was the decreasing transverse resistivity with increased frequency, whereas the parallel resistivity was nearly constant for each frequency. The parallel specific AC impedance of these specimens decreased with increasing measurement frequency, regardless of alignment frequency, indicating dielectric behavior. For amine functionalized MWCNTs, the DC resistivity did not change appreciably among the specimens prepared with or without electrical field. Although the DC resistivity had essentially no anisotropy in these cases, it was 5-8 orders of magnitude less than DC resistivities obtained with the non-covalently functionalized MWCNTs. The parallel AC impedance of these specimens was constant up to a frequency of 100k Hz, indicating ohmic behavior.