Crack-induced Ag nanowire networks for transparent, stretchable, and highly sensitive strain sensors.

Crack-based strain sensor systems have been known for its high sensitivity, but suffer from the small fracture strain of the thin metal films employed in the sensor which results in its negligible stretchability. Herein, we fabricated a transparent (>90% at 550 nm wavelength), stretchable (up to 100%), and sensitive (gauge factor (GF) of 30 at 100% strain) strain gauge by depositing an encapsulated crack-induced Ag nanowire (AgNW) network on a hydroxylated poly(dimethylsiloxane) (PDMS) film. Stretching the encapsulated AgNWs/PDMS resulted in the formation of a percolation network of nanowire ligaments with abundant percolation paths. The encapsulating polymer was designed to adhere strongly to both the AgNW and PDMS. The improved adhesion ensured the resistance of the crack-induced network of AgNWs varied reversibly, stably, and sensitively when stretched and released, at strains of up to 100%. The developed sensor successfully detected human motions when applied to the skin.

Silver Nanowire/Colorless-Polyimide Composite Electrode: Application in Flexible and Transparent Resistive Switching Memory.

Improving the performance of resistive switching memories, while providing high transparency and excellent mechanical stability, has been of great interest because of the emerging need for electronic wearable devices. However, it remains a great challenge to fabricate fully flexible and transparent resistive switching memories because not enough research on flexible and transparent electrodes, for their application in resistive switching memories, has been conducted. Therefore, it has not been possible to obtain a nonvolatile memory with commercial applications. Recently, an electrode composed of a networked structure of Ag nanowires (AgNWs) embedded in a polymer, such as colorless polyimide (cPI), has been attracting increasing attention because of its high electrical, optical, and mechanical stability. However, for an intended use as a transparent electrode and substrate for resistive switching memories, it still has the crucial disadvantage of having a limited surface coverage of conductive pathways. Here, we introduce a novel approach to obtain a AgNWs/cPI composite electrode with a high figure-of-merit, mechanical stability, surface smoothness, and abundant surface coverage of conductive networks. By employing the fabricated electrodes, a flexible and transparent resistive memory could be successfully fabricated.

Highly Stretchable and Waterproof Electroluminescence Device Based on Superstable Stretchable Transparent Electrode.

Realization of devices with enhanced stretchability and waterproof properties will significantly expand the reach of electronics. To this end, we herein fabricate an elastic transparent conductor that comprises silver nanowires (AgNWs) on a hydroxylated polydimethylsiloxane (PDMS) substrate covered by polyurethane urea (PUU), which is fully compatible with both materials. Carboxylic acid groups of PUU was designed to form hydrogen bonds with the carbonyl groups of poly(vinylpyrrolidone) on the AgNW surface, resulting in an enhanced affinity of AgNWs for PUU. Exceptionally strong hydrogen bonds between PUU and the hydroxylated PDMS thus facilitate the achievement of water sealable, mechanically stable, and stretchable transparent electrodes. To fabricate stretchable electroluminescence (EL) devices, ZnS particles were mixed with PUU, and the mixture was coated onto the AgNWs/hydroxylated PDMS, followed by a face-to-face lamination with another identical electrode. The devices could be stretched up to 150% without a severe reduction in the emission intensity, and they survived 5000 cycles of 100% stretch-release testing. The high adhesion between PUU and PDMS even in water is responsible for the good waterproof characteristics of the EL devices. These results pave the way for realization of fully stretchable and waterproof electronic devices.