A geometric percolation model for non-spherical excluded volumes

This paper presents experimental evidence that the percolation threshold in conductor-insulator composites can be a function of the particle size ratio of the constituents, as well as the particle shape. This trend in percolation threshold is to be expected when the conducting particles are excluded from regions of the composite volume (e.g. the core of the insulator particles). The composite system investigated consisted of carbon black powder dispersed in PTFE powder. The system and the method of composite preparation was chosen specifically to promote the realization of this effect. The purpose of this experimental investigation was to provide additional confidence in a recently reported genetic algorithm-based approach to analysing the dielectric spectra of percolative composites. The experimental results are compared to a range of geometric percolation models and one such model is adapted to account for ellipsoidal insulator particles. Good agreement between model and experiment is achieved when this modification is used in conjunction with the actual particle size distribution of the insulator particles.