Flavin Mononucleotide-Mediated Formation of Highly Electrically Conductive Hierarchical Monoclinic Multiwalled Carbon Nanotube-Polyamide 6 Nanocomposites

Although the multiwalled carbon nanotube (MWNT) is a promising material for use in the production of high electrical conductivity (sigma) polymer nanocomposites, its tendency to aggregate and distribute randomly in a polymer matrix is a problematic issue. In the current study, we developed a highly conductive and monoclinically aligned MWNT-polyamide 6 (PA) nanocomposite containing interfacing flavin moieties. In this system, the flavin mononucleotide (FMN) initially serves as a noncovalent aqueous surfactant for individualizing MWNTs in the form of FMN-wrapped MWNTs (FMN-MWNT), and then partially decomposed FMN (dFMN) induces crystallization of the PA on the MWNTs. The results of experiments performed using material subjected to partial dissolution of PA matrix show that the nanocomposite PA-dFMN-MWNT, formed by melt extrusion of PA and dFMN-MWNT, contains a three-dimensional monoclinic MWNT network embedded in an equally monoclinic PA matrix. An increase in monoclinic network promoted by an increase in the content of MWNT increases sigma of the nanocomposite up to 100 S/m, the highest value reported for a polymer-MWNT nanocomposite. X-ray diffraction along with transmission electron microscopy reveal that the presence of dFMN induces the formation of monoclinic PA on dFMN-MWNT. The high sigma of the PA-dFMN-MWNT nanocomposite is also a consequence of a minimization of defect formation of MWNT by noncovalent functionalization. Hierarchical structural ordering, yet individualization of MWNTs, provides a viable strategy to improve the physical property of nanocomposites.