High-Resolution Printable and Elastomeric Conductors from Strain-Adaptive Assemblies of Metallic Nanoparticles with Low Aspect Ratios

Stretchable conductors capable of precise micropatterning are imperative for applications in various wearable technologies. Metallic nanoparticles with low aspect ratios and miniscule sizes are preferred over metallic nanowires or nanoflakes for such applications. However, nanoparticles tend to lose mutual contact during stretching. Therefore, they are rarely used alone in stretchable conductors. In this study, electronic inks comprising silver nanoparticles (AgNPs) for the high-resolution printing of stretchable conductors are reported. AgNPs are synthesized using aqueous polyurethane micelles, which are subsequently disentangled into polymeric chains in isopropanol to stabilize the inks. The ink rheology can be arbitrarily tuned to allow direct-write printing with a minimum feature width of 3 µm. Owing to the absence of extra surfactants, direct drying of such inks at room temperature provides the stretchable conductors with an initial conductivity of 8846 S cm^-1 and conductivity of 1305 S cm^-1 at 100% strain. This enhanced performance is attributed to the conductive percolations through assemblies of AgNPs adapting to the strain and is equivalent to those of stretchable conductors filled with Ag nanowires or flakes. These inks are promising for the scalable fabrication of highly integrated stretchable electronics.