Conducting network formation in drying binary colloidal films

Conductive composite films are fabricated by drying colloidal suspensions containing conducting and insulating particles. We propose a numerical approach to investigate the relationship among fabrication conditions, microstructure, and electrical conductivity in composite colloidal films. Langevin dynamics simulations are first performed to form the microstructure of colloidal films. The electrical conductivity of the films is then evaluated through an equivalent circuit of conducting particle networks, while the distribution of conducting particles is assessed by analyzing Morisita's index of dispersion. Using this numerical approach, we demonstrate that increasing the size ratio between insulating and conducting particles improves electrical conductivity, but this improvement has a limit. This behavior reflects the aggregation of conducting particles in the gap between insulating particles. The present study suggests that controlling the aggregation of conducting particles through fabrication parameters other than particle size ratio is crucial to further improving the electrical conductivity.