Vertical graphene-decorated carbon nanofibers establishing robust conductive networks for fiber-based stretchable strain sensors

Stretchable strain sensors have great potential for diverse applications including human motion detection, soft robotics, and health monitoring. However, their practical implementation requires improved repeatability and stability along with high sensing performances. Here, we utilized spiky vertical graphene (VG) sheets decorated on carbon nanofibers (VG@CNFs) to establish reliable conductive networks for resistive strain sensing. Three-dimensional (3D) VG@CNFs combined with reduced graphene oxide (rGO) sheets were simply coated on stretchable spandex fibers by ultrasonication. Because of the spiky geometry of the VG sheets, VG@CNF and rGO exhibited enhanced interactions, which was confirmed by mode I fracture tests. Due to the robust conductive networks formed by the VG@CNF and rGO hybrid, the fiber strain sensor exhibited a significantly improved strain range of up to 522% (with a high gauge factor of 1358) and stable resistance changes with minimal variation even after 5000 stretching–releasing cycles under a strain of 50%. In addition, the textile strain sensor based on the VG@CNF/rGO hybrid showed even improved repeatability for various strain levels of 10% to 200%, enabling its implementation on leggings for monitoring of squat posture. This study demonstrates the high potential of the 3D VG@CNF for high-performance and reliable stretchable strain sensors.