Hydrophobic and Stable Graphene-Modified Organohydrogel Based Sensitive, Stretchable, and Self-Healable Strain Sensors for Human-Motion Detection in Various Scenarios

Developing stretchable/wearable strain sensors in different application scenarios is a global demand for creating a smart society and promoting healthcare, whereas existing hydrogel-based strain sensors suffer from limited sensitivity, low conductance and hydrophilicity, making them difficult to operate underwater. In this work, a highly sensitive, stretchable, and hydrophobic strain sensor is fabricated by coating a layer of reduced graphene oxide (rGO) sheets on the surface of organohydrogel. Furthermore, a facile solvent-replacement approach is utilized to enhance the anti-freezing and anti-drying abilities of hydrogel simultaneously by incorporating propanediol in the solvent. Consequently, the obtained rGO-organohydrogel composite strain sensor features a high gauge factor of 140, a low detection limit of 0.1% strain, a wide detection range (0-400% strain), a fast response time of 190 ms, excellent stability and repeatability, and high hydrophobicity (contact angle of 122°), making it applicable for a wide range of application scenarios, such as the real-time and continuous monitoring of various human motions in extremely cold (-60 °C), dry, and underwater environments. The sensitivity of an rGO-modified organohydrogel strain sensor is more than 30 times higher than that of its unmodified counterpart, which is attributed to the cracking and tunneling effects introduced by the highly conductive rGO surface layer upon stretching.