Highly Stretchable Strain Sensors Based on AgNWs/PV A Nanocomposite Hydrogels

Here, we report the design, fabrication, and sensing application of highly flexible, conductive hydrogels by embedding conductive silver nanowires (AgNWs) into polyvinyl alcohol (PVA). Two different configurations have been designed including a single layer composite structure and a bilayer structure. The single layer composite was fabricated by direct mixing AgNWs with PVA solution of high concentration (20 wt%). In contrast, a bilayer structure consisted of a bottom PVA layer (20 wt%) and a top layer made of AgNWs and PVA solution of much lower concentration (6 wt%). Both structures exhibited outstanding mechanical properties with high stretchability up to 500% and 600% strain for single layer composite and bilayer structure, respectively. The bilayer hydrogel exhibited a sensitivity (gauge factor) of 0.23 in the strain range of 50 to 250% while the single layer composite structure showed a sensitivity of 0.1 in this range. Overall, the bilayer structure displayed better performance including higher electrical conductivity and piezoresistive sensitivity, larger stretchability, and more stable piezoresistivity. These findings make the PV A-AgNWs/PVA bilayer composite as a potential candidate for strain sensor application.