Electronic transport properties of conducting polymers and polymer blends

We present conductivity and thermopower data for polyaniline (PANI) blends with non-conducting polymers, making a comparison with polyacetylene and discussing general models for conduction. As expected, blending PANI with PET (polyester) reduces conductivity. More unexpectedly, blending with PMMA (polymethylmethacrylate) and PVC can increase conductivity, especially at lower temperatures; this increase is ascribed to lessening of insulating barriers around PANI particles in these blends. The temperature dependence of conductivity in the PANI blends is surprisingly similar to that seen in polyacetylene; it is well described in both types of material by a series combination of quasi-ID metallic resistivity and tunnelling (between small metallic islands for the blends and lightly-doped polyacetylene, and between extended metallic regions in highly-conducting polyacetylene). This heterogeneous model for conduction can also account for some puzzling features of the data in highly-conducting polyacetylene; the large interaction and localization effects seen at low temperatures despite conductivities similar to good metals, the similarity of temperature dependence despite large differences in conductivity magnitude, and the simple linear increase of thermopower with temperature despite the complex temperature dependence of conductivity. The thermopowers of the PANI/PET and PANI/PMMA blends are small and also increase as temperature increases.