Stretchable and highly sensitive graphene-on-polymer strain sensors

Abstract

The use of nanomaterials for strain sensors has attracted attention due to their unique electromechanical properties. However, nanomaterials have yet to overcome many technological obstacles and thus are not yet the preferred material for strain sensors. In this work, we investigated graphene woven fabrics (GWFs) for strain sensing. Different than graphene films, GWFs undergo significant changes in their polycrystalline structures along with high-density crack formation and propagation mechanically deformed. The electrical resistance of GWFs increases exponentially with tensile strain with gauge factors of ~10(3) under 2~6% strains and ~10(6) under higher strains that are the highest thus far reported, due to its woven mesh configuration and fracture behavior, making it an ideal structure for sensing tensile deformation by changes in strain. The main mechanism is investigated, resulting in a theoretical model that predicts very well the observed behavior.

Figure 1. GWF-on-PDMS structure for tensile test.

(a) Schematic of the GWF-on-PDMS structure. (b) Macroscopic optical image of a wired sample. (c) A series of optical images showing the formation of crack and their evolution in GWF under different strain, and corresponding schematics. (d) Optical images of the GWF under large strains (20% and 50%).

Figure 2. Electromechanical behavior of the graphene-on-PDMS strain sensors.

(a) The changes in current and resistance (inset) under different strain. (b) Current response at different static strain. (c) Current response at different frequency under 5% strain. (d) Current and relative changes in resistance (inset) of graphene film. All samples were tested under a bias of 1 V.

Figure 3. Gauge factors of the GWF-on-PDMS strain sensor.

Figure 4. Fracture model of GWF.

(a) Schematic structure of polycrystalline graphene (top) and the critical strain versus graphene sheet size plot (bottom). (b) The equivalent circuit model for estimating the resistance of GWF's with specified cracked GMRs. (c) Current pathway through a fractured GWF. (d) Calculated resistance changes of GWFs with different configurations.

Figure 5. Universal strain sensing.

(a) Compression. (b) Torsion. (c) Shearing. Top panels: schematics and photographs, bottom panels: corresponding changes in resistance under different deformation. The sensing behavior depends on the dimensions of PDMS and GWF. All GWF samples are ~1×1 cm².