Conduction development in electrically conductive adhesives with a bimodal size distributed conducting and inert particles: effect of polydispersity

A well known approach for reducing the electrical percolation threshold of an electrically conductive material is to mix the relatively small sized conducting fillers with the relatively large sized inert particles. The percolation limit in terms of the volume fraction of conducting particles is known to decrease with increasing ratio of the mean size between the small and large particles. However, both the small conducting and large inert particles rarely exist as monodispersed, rather, there is a respective size distribution for each of them. Such a size distribution is expected to affect the development of conductivity as well as the percolation threshold. The first theoretical model for considering such a size dispersity effect on the conduction development and the percolation limit is reported. It is shown that the present model not only includes all the previous ones for considering only the particle size ratio effect, it considers the respective role played by the ratio of mean particle size, the size dispersity and the volume fraction on the electrical conduction development and the percolation limit. The model suggests an innovative route for processing new conductive adhesives with ultralow percolation limits. Other implications for manufacturing electrically conductive adhesives are also discussed.