Effect of Area Density on Sensitivity and Strain Survival of Reduced Graphene Oxide Under Large Strains

Abstract

Abstract Strain sensors are the primary, direct sensing element in many sensors with applications in robotics, wearable sensors, structural health monitoring, and beyond. Cutting edge applications are increasing demand for sensors that can survive and measure large strains (> 5%). Presently, the most common strain sensors are composed of a serpentine metal foil which can survive strains up to about 5% with a gauge factor (GF) of about 2 (measured as change in resistance divided by initial resistance all over strain). Research into nanoparticle-based strain sensors commonly reports surviving strains up to 50% and gauge factors around 200. Unfortunately, most nanoparticle-based strain sensors are composed of expensive, toxic materials and require high precision synthesis methods. The reduced Graphene Oxide (rGO) based sensors can be synthesized easily with common materials and methods. Study of strain sensing capabilities have revealed that rGO strain sensors can survive strains beyond 15% with gauge factors (sensitivity) on the order of 200. Suspensions of graphene oxide (GO)’s flakes were deposited on flexible Polydimethylsiloxane (PDMS) substrates to create specimens with different area densities of 0.69, 0.80 and 091 mg/cm2 of GO. Specimens were thermally reduced to create rGO-based strain sensors. Resulting sensors were tested under tension applied at a rate of 0.1 mm/sec starting from 0% strain until failure. Resistance of the sensors in the direction aligned with the direction of the applied tension were measured at each 1 mm-increment of tension. Sensitivity and the strain to failure of the sensor were calculated and compared in specimens with different GO area densities. Our study suggests that with increasing the area density of graphene oxide (GO) during the synthesis of rGO, the survivability of the rGO subjected to large strains can be improved while still demonstrating a high sensitivity. This study can help tailor rGO-based strain sensors especially to the applications where high strain survival (> 30%) is required while benefiting from a reasonably good GF (> 30).