A novel polyimide dispersing matrix for highly electrically conductive solution-cast carbon nanotube-based composite

Multiwalled carbon nanotubes (MWNTs) have high intrinsic conductivities and are thought to be ideal fillers for electrically conductive composites. However, so far, simple solution casting or blending of nanotubes has not been highly successful in producing highly conductive composites, because of the poor dispersion and low loading of the nanotubes. We show that, by using a novel poly(amic acid) (PAA) containing a rigid backbone with hydroxyl pendant groups, as both the nanotube dispersant and the matrix precursor, we can increase the nanotube content in the solution-cast polyimide (PI)-based composite to as high as 30 wt % and achieve ultrahigh composite electrical conductivity as well as high mechanical properties. The electrical conductivity of the MWNT/PI composites reaches a value of 38.8 S cm^-1 at a nanotube loading of 30 wt % and the MWNT concentration for achieving the percolation threshold of conductivity of the composites is 0.48 wt %. These are, respectively, the highest and among the lowest reported values for any conventional solution-processed nanotube composites. The 30 wt % MWNTs composite has a higher Young's modulus (9.43 ± 0.14 GPa) and tensile strength (179.2 ± 9.7 MPa) than other nanotube-reinforced polyimide composites. The high conductivity, as well as tensile properties, of the composite films is attributed to the good nanotube dispersion and strong nanotube-polymer interfacial adhesion achieved through use of a single polymer to perform the dual functions of nanotube dispersant and matrix precursor. The excellent properties, combined with the facile conventional solution-casting technique, make this MWNT/PI composite film a promising material for many potential applications. We have also demonstrated that uniform MWNT(30 wt %)/PI composite coatings can be deposited onto glass and aluminum substrates.