Enhanced conductivity induced by attractive capillary force in ternary conductive adhesive

Materials with advanced conductive properties are in high demand to fulfill the requirements of energy transport in many fields. Here, we present a simple, efficient yet low cost method to produce highly conductive polymer based composites at low filler concentration of 10 vol%. A particle-wetting fluid as a secondary fluid is introduced to bridge plate-shape silver particles within an epoxy base. The electrical and thermal conductivity dependence on network structure in ternary silver adhesive presenting strong capillary attraction was first reported. Both electrical and thermal conductivities are greatly enhanced by introducing the secondary fluid at a low particle volume fraction of 10%. A non-monotonic dependence of the conductivities on secondary fluid content was observed. The maximum electrical and thermal conductivities correspond to the formation of full pendular network and funicular network, respectively. Gradually increasing the secondary fluid content leads to a microstructure evolution from highly dispersed particles, weak gel network, full pendular network, funicular network and ultimately to compact capillary aggregates network. Such structural transition appears to result from a pendular bridge formation and bridges coalescence. Face-face configuration of plate-shaped silver particles was observed in the pendular state. Taking account of the highly non-spherical shape of silver flake, a bridging gelation model is proposed to explain the underlying mechanism of microstructure transition.