Cellular Graphene: Fabrication, Mechanical Properties, and Strain-Sensing Applications

Abstract

We provide a review of cellular graphene (CG), from its fabrication, to characterization of mechanical properties, to applications in strain and pressure sensing. Although several recent reviews have briefly surveyed various types of strain and pressure sensors fabricated from common one-dimensional or two-dimensional (2D) nanomaterials such as carbon nanotube (CNT), graphene, and metallic nanowire/nanoparticle, the emerging applications of CG in the design and development of strain and pressure sensors, as well as the structure-property-function correlations in sensing performance, have not been systematically covered. CG exhibits unique strain-sensing capabilities that collectively enable a wide range of strain sensing to be achieved. We first review several state-ofthe-art approaches for fabricating CG with emphasis on the engineering of tailored mechanical properties. Second, the strain-and pressure-sensing performance of CG-based devices against a range of fabrication processes is systematically and critically analyzed. Along the way, representative applications of such CG-based sensors are thoroughly discussed. This review aims to provide basic information for the design of novel CG as well as other classes of threedimensional porous structures fabricated from various 2D nanomaterials. In the conclusion, we highlight the extension of design principles to other 2D materials and critically summarize the key issues that need to be addressed in the future.

Fabrication of reduced graphene oxide modified poly(3,4-ethylenedioxythiophene) polystyrene sulfonate based transparent conducting electrodes for flexible optoelectronic application

“…6a. The increase in resistance on outward bending is due to tensile stresses that tend to separate the layer particles from each other [38]. In a similar way, electrical resistance variation as a function of inward bending curvatures of rGO/PEDOT: PSS hybrid layer was measured and shown in Fig.…”

Highly Sensitive Strain Sensor from Topological‐Structure Modulated Dielectric Elastic Nanocomposites

“…Despite of their high gauge factor, the irrecoverable deformations of conductive network usually leads to nonlinear behavior and inferior stability for strain sensors. [ 8–10 ] Capacitive sensors response mechanical stimuli by means of capacitance change, which is mainly attributed to change of geometric structure of devices (e.g., effective area and thickness of the dielectric layer). Capacitive strain sensors exhibit significant advantages in linear behavior, stability, and integrated circuits.…”

“…Capacitive strain sensors exhibit significant advantages in linear behavior, stability, and integrated circuits. [ 10–12 ] Flexible sensors have also been fabricated by design of delicate microstructures, such as hierarchical nano‐in‐micro structure, sponge‐like, pyramids, microhairs, and fabric, and have been used in electronic skins. [ 13–17 ] While capacitive strain sensors based on structures design still exist some inherent defects, including low signal‐to‐noise ratio, limited sensitivity (negative values for interdigital strain sensors), and poor mechanical conformability.…”

Detecting subtle yet fast skeletal muscle contractions with ultrasoft and durable graphene-based cellular materials

“…Thus sensors based on soft and mechanically durable materials such as rubber have received increasing attention in recent years. Among the variety of soft wearable sensors, rubber-based resistive strain sensors have been widely exploited for monitoring different types of human physical activities because of their combination of softness, low-cost and easy signal reading and interpretation [ 5 , 6 , 14 , 16 – 18 ]. However, human bodily activities are extremely dynamic and complex and different bodily motions exhibit distinct strain and frequency features.…”

“…For example, joint movements can induce large skin strain up to 55% [ 6 , 19 ] but with a low frequency (<5 Hz); in contrast, inner skeletal muscle fibre contractions are more subtle, with strains as low as 0.5% of the muscle length [ 20 , 21 ], but their frequency can reach up to 40 Hz [ 22 – 24 ]. To our knowledge, previous research on wearable resistive strain sensors has been primarily centred on monitoring different gross skeletal movements such as gait, posture, locomotion or other voluntary movements [ 3 , 5 , 16 , 17 , 19 , 25 – 33 ]; little success has been made in the use of flexible soft materials to assess minute neuromuscular–skeletal interactions and more subtle and particularly high-frequency skeletal muscle fibre contractions, likely limited by the viscoelasticity of polymeric elastomers, which would inevitably result in a relatively slow response or delayed recovery. Therefore, the development of soft, stretchable, mechanically durable yet highly sensitive electroconductive materials for detection of complex, subtle and high-frequency dynamic neuromuscular activities represents a significant challenge.…”