Hierarchical\nReduced Graphene Oxide Ridges for Stretchable,\nWearable, and Washable Strain Sensors

Abstract

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