Effect of the Type of a High-Temperature Polymer Matrix on the Morphology and Electrical Conductivity of Composites with SWCNTs

Electrically conductive composite materials based on polybenzimidazole and aromatic polyamide matrices with single-walled carbon nanotubes (SWCNTs) are studied. Composites are obtained from SWCNT dispersions in solutions of polybenzimidazole and aromatic polyamide in N-methyl-2-pyrrolidone by the same procedure. Composites based on the poly-2,2′- p -oxydiphenylene-5,5′-dibenzimidazole (OPBI) matrix with a SWCNT concentration less than 1 wt.% are shown to be not electrically conductive unlike those based on the poly- m -phenylene-isophthalamide (MPA) matrix (electrically conductive even with a SWCNT concentration of 0.1 wt.%). This feature is related to different morphologies of the composites: in OPBI-based composites, nanotubes are more effectively separated by the polymer matrix due to the π–π interaction of OPBI macromolecules with SWCNTs. The microstructure is analyzed by scanning and transmission electron microscopy. It is revealed that in the case of the OPBI- matrix, nanotubes are separate SWCNTs or bundles with a smaller diameter and a more uniform volume distribution compared to the MPA-matrix. This feature of the morphology is reflected in temperature dependences of the electrical resistance measured from room temperature down to 4.2 K. In the case of the OPBI-matrix, the electrical resistance changes more with temperature, which also indicates the better separation of SWCNTs in the OPBI- matrix than in the MPA one.