Effect of the rigidity of polyimide matrices on the electrical conductivity of graphene-containing composites

There is an increasing demand for polyimide-based conductive composite materials with excellent mechanical properties and good thermostability for engineering and biomedical applications. A strategy has been proposed to produce composites based on polyimide matrices of various rigidities filled with graphene particles. The results of dynamic mechanical analysis demonstrate that the values of glass transition temperature and elastic modulus of these composites increase (from 3.1 GPa to 9.6 GPa) with increasing rigidity of the PI matrix. An increase in the PI rigidity also leads to a decrease in volume conductivity of samples (from 10^–4 to 5 × 10^–7 S/m), while their surface conductivity increases (from 0.04 S/m to 2 S/m). Apparently, this is due to expulsion of graphene into the near-surface area of the composite film, which is confirmed by independent methods (X-ray photoelectron spectroscopy and IR spectroscopy). The macromolecules of rigid-chain polyimide demonstrate planar orientation, which facilitates the appearance of strong π–π-interactions between monomer units of polymer chains and prevents uniform distribution of graphene particles within the volume of this polyimide matrix.