On the electrical conductivity of PVDF composites with different carbon-based nanoadditives

Composites based on poly(vinylidene fluoride) (PVDF) and different carbon additives, such as carbon nanofibers (CNF), graphite (G), expanded graphite (EG), and single-walled carbon nanotubes (SWCNT) have been prepared by nonsolvent precipitation, from solution, and subsequent melt processing. From a structural point of view, the α-crystal phase is the predominant crystal form in all the nanocomposites. However, those containing CNF, G, and EG at high nanoadditive content present also β-crystal phase. Even though the intrinsic thermal properties of PVDF are hardly affected, the nanoadditives act as nucleating agents for the crystallization. In regard to the electrical properties, all nanocomposites exhibit a percolating behavior. Moreover, the fact that the nanocomposites present both high dc conductivity and high dielectric constant, in a certain nanoadditive concentration range below the percolation threshold, suggests that a tunneling conduction mechanism for charge transport is present. With regard to the ac electrical properties, depending on the morphology of the different additives, the charge transport above percolation threshold can be explained taking into account the anomalous diffusion effect for high nanoadditive content or an intercluster polarization mechanism when the nanoadditive concentration decreases.