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

Abstract

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.

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

“…A crucial step in the design of stretchable strain sensors is the selection of appropriate materials, assembled structures, and fabrication methods. Various conductive materials including carbon nanomaterials (e.g., carbon blacks [CBs], carbon nanotubes [CNTs], graphene and its derivatives), [6,9,34,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] metal nanowires (NWs), nanofibers (NFs), and nanoparticles (NPs), [8,16,[71][72][73][74][75][76][77][78][79] MXenes (e.g., Ti 3 C 2 T x ), [10,80,81] ionic liquid, [82,83] hybrid micro-/nanostructures, [84][85][86][87][88][89][90][91][92][93]…”

“…Stretchable strain sensors based on NWs and flakes particularly take advantage of the disconnection mechanism. [1,8,37,55,57,144,172] For instance, the resistance shift in stretchable strain sensors made of Ti 3 C 2 T x MXene/CNTs films coated over the latex substrate was reported to be due to the changes in the overlapping areas and interconnecting pathways during cyclic stretching-releasing. [81] Similar behavior has been observed in the conductive network of Au nanosheets dropcast on the Ecoflex substrate.…”

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…More and more building blocks such as metal coatings, low-dimensional materials, and semiconductors were used to fabricate functional wrinkled structures on curved substrates, and meanwhile a number of novel topographies such as wrinkled architectures, highly compressed self-contact creases, highly convoluted interlocked structures, largearea crack-free crumpled films, and wrinkled hollow structures have been achieved by controlling parameters like the core-shell modulus ratio, substrates curvature, shell thickness, and deformation models. These wrinkled morphologies with special properties remarkably extend the applications of structured curved surfaces to superelastic electronics, bionic actuators, controllable adhesion, chemical protection, artificial vascular, and inflatable devices [53][54][55][56][57][58][59][60][61][62][63][64].…”

“…Therefore, surface wrinkling of thin stiff shells on hollow soft substrates will be the center of this section. Compared with solid core-shell systems, the expansion and contraction of hollow soft spheres and cylindrical tubes composed of elastic walls can be induced by inflation and deflation, and the contractioninduced compressive stress in the shells can be regulated by varying the pressure difference [54,55,61,157,199]. For hollow core-shell systems with thick walls (≥ 10 mm), directly pumping the air from the cavity is an efficient way to generate homogeneous compression in the shell, and sufficiently large compressive stress is able to trigger surface instability.…”

Highly Sensitive E-Textile Strain Sensors Enhanced by Geometrical Treatment for Human Monitoring

“…Chen et al [17] prepared a PPy-coated stretchable textile via a low-temperature interfacial polymerization method to function as a sensitive sensor. Many other studies on stretch sensors [18][19][20][21][22] were conclusively proven to have highly sensitive materials suitable for wearable devices. However, all of the above studies pay particular attention to complex materials or fabrication technologies that will increase the difficulty in the manufacturing process, cost, and ability in mass production.…”