Stretchable and Electrically Conductive Composites Fabricated from Polyurethane and Silver Nano/Microstructures

Stretchable conductive composites have received considerable research interest recently for high-end microelectronic applications. Here we report conductive and stretchable composites by incorporating various shape-modified silver fillers into polyurethane elastomer matrix. By selecting soft and hard segments of polyurethane, the polymer resin can not only provide sufficient stretchability/flexibility, but also serve to reduce the surfactants on silver surface due to the presence of hydroxyl groups. Three conductive fillers, including commercial silver flakes, synthesized silver nanowires and three-dimensional silver dendrites were employed. The conductive composites could achieve resistivity as low as 5×10-5 .cm at using 80 wt% of silver flakes. The silver nanowires, with aspect ratio higher than 100, can achieve low electrical percolation threshold. The silver dendrite were prepared by a simple solution process with the capability for scalable production at low cost. The branched nano/microstructures can be delicately controlled by tuning the feeding speed and molar ratio of the silver precursor and reducing agent. Without any surface treatment, the bulk resistivity of the printed composite films was ~ 8×10-4 .cm at 70 wt% filler loading. The design of the conductive fillers within compatible elastomers show great potentials for portable and wearable electronic devices.