Metal-Free and Stretchable Conductive Hydrogels for High Transparent Conductive Film and Flexible Strain Sensor with High Sensitivity

Conductive hydrogels show promising applications in wearable electronic devices. However, it is still challenging to increase the conductivity as well as the mechanical performance of the conductive hydrogels. In addition, it is more challenging to fabricate ultrathin conductive films with good mechanical strength and high transparency. In this study, a metal-free flexible conductive hydrogel for flexible wearable strain sensor with high sensitivity is presented. The conductive hydrogel is prepared by polyvinyl alcohol (PVA) templated polymerizing of polypyrrole (PPy) followed by gelating based on the polymerizing and cross-linking of polyacrylamide (PAAm). The conductive hydrogel is endowed excellent mechanical properties by multiple hydrogen bonds between the interpenetrating network of PVA, PPy, and PAAm. The tensile strength reaches up to 0.2 MPa at 500% and the compression strength reaches up to 1.5 MPa at 90%. It can withstand cyclic loads. The conductivity reaches 0.3 s m(-1) and it is sensitive to stretching and compressing. Therefore, strain sensors are prepared based on such hydrogels to make wearable electronic devices, monitoring the subtle and large strains. It is worth noting that the composite material containing PVA has good film-forming properties. Therefore, ultrathin conductive hydrogel films with high transparency (94.2%), high conductivity (7090 omega/square) and large-area are fabricated at low cost.