Shape Engineering of the Fillers in Stretchable, Electrically Conductive Adhesives: Its Effect on Percolation and Conductivity Change during Stretching

The effects of different shapes of silver; particles, flakes and dendrites on the electrical property of polydimethyl siloxane (PDMS)-based electrically conductive adhesives (ECA) under mechanical deformation are investigated. It is found that the high aspect ratio of silver dendrites helps to construct more conduction pathways in the ECAs compared with silver particles and flakes, therefore reducing the percolation threshold. Stretching made the bulk resistivity of spherical silver filled ECA increase exponentially, which is in good agreement with the classical piezoresistive models. On contrast, the resistivity of silver flakes filled ECAs did not change within 100% strain and up to 500 cycles of stretching/releasing tests. For silver dendrites, the resistivity decreased when stretching and increased slightly afterwards, resulting in an almost invariant value within 60% elongation. However, removing the external strain did not havethe resistance value recover back to the original level.