Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Abstract

Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.

A graphene rheostat for highly durable and stretchable strain sensor

“…This feature allows the strain sensor to bear the strain with minimized microstructural fracture, indicated by the closed loop of relative resistance change ΔR/R 0 (ΔR: variation of electrical resistance, R 0 : electrical resistance under no strain) as function of strain even at 10000th cycle ( Figure S2). It is principally different from the contact area variation resulted from the in-plane slippery of conductive materials (eg, CNTs, 19,21 graphene, 27,31,32 and nanowire 34,36 ) as shown in the previous reports ( Figure 2C). Due to the lack of three-dimensional structural coordination, the deformation cannot be recovered based on the random generation of the touching position and upon strain releasing.…”

“…C, The schematic of graphene "slide-rheostat" and in-plane slippery of graphene sheets. TEM, transmission electron microscope described in the previous studies, because of the lack of the three-dimensional structural coordination, the distance between the conductive materials and the outer polymer 26,32 or the cracking propagation 30 was always occurred to the structure upon the loading/unloading, giving rise to the irreversible increase of "R 0 " or "current" (seen as the big gap/shift in their values between the loading and unloading), which is indeed the general problem for limited stability raised from the structural design of devices by far. In contrast, our "slide rheostat" design of our material ensures the cyclic variation of electrical resistance based on the local slippage, giving rise to the almost full recovery of relative resistance change (ΔR/R 0 ) to the initial state ( Figure S2a).…”

“…One possible solution is to mix graphene with super‐elastic rubber, which could be stretched to 800% with the gauge factor of 35; however, the cyclability (10 3 cycles) is still rather limited . Other attempts include integrating graphene into polymeric fibers or constructing graphene sheets into fragments, resulting in improved performance (up to 10 4 cycles at the strain of 50%). Recently, the configuration of fish‐scale‐like graphene in two‐dimensional mode realized 5000 cycles stability at the strain of 10%, yet failed to demonstrate high‐strain (>60%) cycle stability due to the lack of structural coordination .…”

“…Various active materials, including carbon nanotubes (CNT), 6,[18][19][20][21] graphene, [22][23][24][25][26][27][28][29][30][31][32] nanoparticle, 33 nanowires, [34][35][36] and conducting polymers 10,15,37,38 have emerged as promising candidate for strain sensors fabrication. Compressible strain sensors made from ultrathin film of single-wall carbon nanotubes (SWCNTs), 6 graphene/polyimide composite foam, 22 and polyurethane nanofibers 38 have been fabricated, and the ultrasensitivity to detect the pressure lower than 1 Pa has been demonstrated.…”

Advanced carbon materials for flexible and wearable sensors

“…16f) due to the fractured microstructures in the sponge. Graphene foams synthesized by CVD were reported to be applicable to fabricate flexible strain sensors with desirable GF [270], which could be attached on human body for monitoring body movements and pulses.…”