Transparent and Flexible Electronics Assembled with Metallic Nanowire-Layered Nondrying Glycerogel

There has been increasing demand for transparent and mechanically durable electrical conductors for their uses in wearable electronic devices. It is common to layer metallic nanowires on transparent but stiff poly(dimethylsiloxane) (PDMS) or stretchable but opaque Ecoflex-based substrates. Here, we hypothesized that layering metallic nanowires on a stretchable and hygroscopic gel would allow us to assemble a transparent, stretchable, and durable conductor. The hygroscopic property of the gel was attained by partially replacing water in the preformed polyacrylamide hydrogel with glycerol. The resulting gel, denoted as a glycerogel, could remain hydrated for over 6 months in air by taking up water molecules from the air. The glycerogel was tailored to be stretchable up to 8 times its original length by tuning the amount of the cross-linker and acrylamide. The resulting glycerogel allowed for deposition of wavy silver nanowires using the prestrain method up to 400% prestrain, without causing kinks and interfacial cracks often found with nanowires layered onto PDMS. With a prestrain of 100%, the resulting nanowire-gel conductor exhibited optical transparency (85%) and electrical conductivity (17.1 ohm/sq) even after 5000 cycles of deformation. The results of this study would broadly be useful to improve the performance of the next generation of flexible electronic devices.