Stepwise percolation behavior induced by nano-interconnection in electrical conductivity of polymer composites

The electrical conductivity of polymer composites incorporating a continuous nanocarbon network is reported to be 1–2 logarithmic orders higher than that of the saturation region in a typical percolation model, indicating the existence of an undiscovered region. In this study, polymer composites with high filler content (∼50 vol%) are fabricated by powder mixing and in situ polymerization including sophisticated humidity control by promoting heat convection using an air fryer. Stepwise percolation behavior is observed, wherein the electrical conductivity of the composite with a high filler content exceeds that of the percolation plateau and further increases (3828% increase at 40 vol% multi-walled carbon nanotube (MWCNT) compared to 35 vol%), and the stepwise behavior is caused by the connected filler network (nano-interconnection). A novel stepwise percolation model that describes the behavior by considering both the tunneling resistance and the nano-interconnection is proposed. In addition, the stepwise percolation behavior induces high levels of electromagnetic interference shielding (236.36% increase at 50 vol% graphene nanoplatelet relative to 40 vol%) and humidity sensing (55.59% improvement at 40 vol% MWCNT compared to 35 vol%) properties. Therefore, derivation of the stepwise percolation behavior based on the nano-interconnection can be a new breakthrough in applications of conductive composites.