Percolation of electrical conductivity in solution-cast blends containing polyaniline

The potential offered by intrinsically conductive polymers is limited by their poor mechanical properties. Blending with common thermoplastics can improve processability and mechanical properties and still preserve the electrical conductivity. In such blends, the morphology determines the mechanical and electrical properties. In this research, blends of polyaniline (PANI)-dodecyl benzene sulfonic acid (DBSA) with either polystyrene (PS) in xylene or polyvinylchloride (PVC) in bromobenzene were solution cast. The morphologies of the blends were characterized by optical microscopy (OM), electron microscopy, and small-angle X-ray scattering (SAXS). Electrical conductivity was measured for various compositions. The formation of a continuous network was strongly associated with percolation and conductivity. The morphologies of the two blends are significantly different. This difference arises from the different solvents used and their ability to swell the PAN1 aggregates and to promote their disintegration into small particles. Molecular calculations show that, indeed, bromobenzene, used in the PVC system, is able to penetrate the PANI-DBSA aggregates, while xylene, used in the PS system, cannot. Nevertheless, the small PANI-DBSA particles in the PVC matrix form a conductive network only at a relatively high content, while the coarse aggregates in the PS matrix form conductive paths at a relatively low content. These results are discussed in terms of the formation and stability of the PANI-DBSA dispersion.