(559c) Electrical Conductivity In Polymer Nanocomposites Containing Metal Nanowires: Simulation and Experiment

The study of percolation behavior has resurfaced in recent years, because this phenomenon dominates the electrical conductivity in polymer nanocomposites. Furthermore, carbon nanotubes and metal nanowires access new size and aspect ratio regimes. This paper will explore this topic using both simulations and experiments.

Traditional percolation theories (i.e. the excluded volume model) are only strictly applicable for rods of effectively infinite aspect ratio. Because many processing techniques used for preparing carbon nanotube composites produce nanotubes with aspect ratios of less than 50, a simulation approach to study percolation behaviors of finite-sized rods is needed. In addition, it is useful to combine the simulation of filler morphologies with calculations of a specific composite property, e.g. electrical conductivity. We will present our simulations of conductive rods in an insulating matrix showing the effects of filler loading, aspect ratio, and degree of uniaxial alignment on electrical percolation behavior and conductivity. As the uniaxial alignment increases, there is a dramatic drop in electrical conductivity, because the network structure is destroyed. This result indicates that the traditional polymer processing methods of extrusion and injection molding are likely to produce materials with unintended heterogeneity in the electrical conductivity due to variations in nanofiller orientation.

Our initial experimental work used carbon nanotubes to probe the effect of axial alignment on nanocomposite conductivity. Here, we use metal nanowires, because the size (diameter and length) can be easily controlled by templated synthesis and all the metal nanowires are metallic, unlike carbon nanotubes. We prepare silver nanowires by electroplating into alumina membranes and then free the nanowires by dissolving the membrane. The polystyrene nanocomposites are then made using our group's established coagulation method. Isotropic and uniaxially aligned nanocomposites are prepared by compression molding and melt fiber spinning, respectively. The morphologies of the nanowires and nanocomposites are determined using a combination of optical microscopy, SEM, and X-ray scattering. The electrical conductivity is measured using a two-probe method and compared with our simulation results.