Hierarchical Reduced Graphene Oxide Ridges for Stretchable, Wearable, and Washable Strain Sensors.

Recently, flexible and wearable devices are increasingly in demand and graphene has been widely used due to its exceptional chemical, mechanical and electrical properties. Building complex buckling patterns of graphene is an essential strategy to increase its flexible and stretchable properties. Herein, a facile dimensionally controlled four-dimensional (4D) shrinking method was proposed to generate hierarchical reduced graphene oxide (rGO) buckling patterns on curved substrates mimicking different parts of the uniforms. The reduced graphene oxide ridges (rGORs) generated on the spherical substrate seem isotropic, while those generated on the cylindrical substrate are obviously more hierarchical or oriented, especially when the cylindrical substrate are shrinking via two steps. The oriented rGORs are superhydrophobic and strain sensitive but obviously anisotropic along the axial and circumferential directions. The sensitivity of rGORs along the axial direction is much higher than those along the circumferential direction. In addition, the intrinsic solvent barrier property of graphene enables the crack-free rGORs an excellent chemical protective performance, withstanding DCM immersion for more than 2.5 h. The flexible rGORs-based strain sensors can be used to detect both large and subtle human motions and activities by achieving high sensitivity (maximum gauge factor up to 48), high unidirectional stretchability (300-530%), and ultrahigh areal stretchability (up to 2690%). Excellent durability was also demonstrated for human motion monitoring with resistance to hand rubbing, ultrasonic cleaning, machine washing, and chemical immersion.