Ultrasensitive and Stretchable Strain Sensors Based on Mazelike Vertical Graphene Network

Here, we report a new type of strain sensors consisting of vertical graphene nanosheets (VGNs) with mazelike network, sandwiched between poly(dimethylsiloxane) (PDMS) substrates. The new sensors outperform most graphene thin-film-based sensors reported previously and show an outstanding combination of high stretchability of ∼120%, excellent linearity over the entire detection range, and high sensitivity with a gauge factor of ∼32.6. The sensitivity can be tuned by controlling the thickness of VGNs, with sensors consisting of thicker VGNs showing higher sensitivity but slightly lower stretchability (the maximum gauge factor is ∼88.4 with a maximum detection strain of ∼55%). Detailed microscopic examinations reveal that the ultrahigh sensitivity stems from the formation of microcracks initiated in the buffer layer. These microcracks are bridged by strings of graphene/PDMS, enabling the conductive network to continue to function up to a strain level significantly higher than that of previously reported graphene thin-film-based sensors. Furthermore, the present sensors have been found to be insensitive to temperatures and various liquids, including water and 0.1 mol L^-1 sodium chloride solution (similar to the sweat on human skin). Demonstrations are presented to highlight the new sensors' potential as wearable devices for human motion detection and pressure distribution measurement.