Flexible and electrically conductive composites based on 3D hierarchical silver dendrites†
Conductive polymer composites have gained increasing popularity as essential components for next-generation flexible electronics. Chemical tuning of the polymer matrix and shape engineering of conductive fillers are two promising routes for material development to improve the electromechanical characteristics. Here we describe highly conductive and flexible polyurethane (PU)-based composites using 3D hierarchical silver dendrite (SD) micro/nanostructures as conductive fillers. The highly crystalline SDs adopt a 6-fold symmetry with high aspect ratio branches, which can be interlocked to provide better electrical contact under strain and sintered at low temperature to reduce contact resistance. By selecting the appropriate chemistry, SD fillers lubricated with surfactants can be well dispersed into PU resin and the surfactants can be in situ removed during the curing process due to the presence of polyols in the formulation. The unique SD structures and modified polymer–filler interface are key elements in realizing excellent electrical and mechanical properties. Specifically, the SD–PU composites demonstrated an ultralow resistivity of 7.6 × 10−5 Ω cm, a low percolation threshold of 3 vol%, minimal resistance change under mechanical strains, and strong adhesion to substrates. The evolution of temperature-dependent resistivity has been correlated with polymer dynamics and sintering behavior to understand the conduction mechanism.