Double-layered cracked networks using vertical graphene grown on carbon nanofibers for highly stable stretchable strain sensors

The increased demand for wearable devices that can be used in various applications requires the development of stretchable strain sensors with high performance and high stability. In this study, we propose double-layered cracked conductive networks to fabricate highly stable strain sensors. The conductive network consists of vertical graphene grown on carbon nanofibers (VG@CNFs) and reduced graphene oxide (rGO). The densely packed VG sheets formed strong interactions with rGO sheets. A robust VG@CNF/rGO hybrid film was partially embedded in an elastomer to create a double-layered conductive film. Due to the double-layer architecture, the bottom layer anchored in the elastomer withstands high strains and maintains the conductive paths, whereas the top layer without elastomer fixation can be easily fractured and induces abrupt changes in the conductive paths. The presence of VG@CNF provided synergy with the double-layered cracked networks, facilitating reversible crack generation and reconstruction of the paths during repeated stretch–release cycles. Therefore, the double-layered strain sensor exhibited superior sensing performance with a stretchability of 144.6 %, sensitivity (gauge factor) of 183.5, and minimal change in the resistance responses during 1000 stretching–releasing cycles, outperforming the CNF-based sensors. The VG@CNF-based double-layered sensors attached to the human body detected both small and large movements.