Chemical functionalization of helical carbon nanotubes for high-performance structural applications of nanocomposites

Helical carbon nanotubes (HCNTs) offer unique geometrical characteristics and capabilities; however, their properties, functionalization, and applications have not been sufficiently explored, compared to the straight CNTs that have different crystallinity and structural characteristics. The coil-shaped geometries of HCNTs can substantially increase their mechanical entanglement/interlocking with solidified host-resins and the microfiber-reinforcements in fiber-reinforced composites. As a result, it can considerably improve the mechanical, thermal, electrical, and magnetic properties of the composites. To further improve their effectiveness, HCNTs should be chemically treated to promote their molecular interactions and bonding-effectiveness with the resin molecules, as well as to enhance their dispersion-uniformity and suspension-stability in the host-resin.

Recently, a reflux method was deployed to chemically functionalize HCNTs with a low-molarity nitric acid-solution and then effects of reflux time and temperature on surface-modification and dispersion-homogeneity of the functionalized HCNTs (FHCNTs) were investigated. The results from SEM, FTIR, XRD, Raman spectroscopy, and visual dispersion-test showed that changes in reflux time and temperature were mostly effective in atomic scale structural alteration of the HCNTs. Except for the FHCNTs that were treated at higher temperatures for a longer time, the rest showed improvements in their dispersion, an increase in I_D/I_G Raman ratios, and changes in FTIR spectra. This work was reported by Frontiers of Materials Science.