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. 2014 Jan 6;14(1):868-76.
doi: 10.3390/s140100868.

Stretchable and flexible high-strain sensors made using carbon nanotubes and graphite films on natural rubber

Sreenivasulu Tadakaluru  1 , Wiradej Thongsuwan  2 , Pisith Singjai  3
Affiliations

Stretchable and flexible high-strain sensors made using carbon nanotubes and graphite films on natural rubber

Sreenivasulu Tadakaluru et al. Sensors (Basel). .

Abstract

Conventional metallic strain sensors are flexible, but they can sustain maximum strains of only ~5%, so there is a need for sensors that can bear high strains for multifunctional applications. In this study, we report stretchable and flexible high-strain sensors that consist of entangled and randomly distributed multiwall carbon nanotubes or graphite flakes on a natural rubber substrate. Carbon nanotubes/graphite flakes were sandwiched in natural rubber to produce these high-strain sensors. Using field emission scanning electron microscopy, the morphology of the films for both the carbon nanotube and graphite sensors were assessed under different strain conditions (0% and 400% strain). As the strain was increased, the films fractured, resulting in an increase in the electrical resistance of the sensor; this change was reversible. Strains of up to 246% (graphite sensor) and 620% (carbon nanotube sensor) were measured; these values are respectively ~50 and ~120 times greater than those of conventional metallic strain sensors.

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Figures

Figure 1.
Figure 1.
Schematic illustration of the steps used to prepare the test samples, which consisted of MWCNTs or graphite coated on NR.
Figure 2.
Figure 2.
(a,b) SEM images of unstrained (0%) and strained (400%) MWCNT-coated NR samples; (c,d) SEM images of unstrained (0%) and strained (400%) graphite-coated NR samples.
Figure 2.
Figure 2.
(a,b) SEM images of unstrained (0%) and strained (400%) MWCNT-coated NR samples; (c,d) SEM images of unstrained (0%) and strained (400%) graphite-coated NR samples.
Figure 3.
Figure 3.
Response curves: (a) Relative resistance and resistance versus strain response curves for the MWCNT sensor; (b) Relative resistance and resistance versus strain response curves for the graphite sensor.
Figure 4.
Figure 4.
Nonlinearity: (a) Non-uniform deformation of the strained conducting layer/substrate; (b) Stress versus strain curves for the MWCNT, graphite coated, and uncoated NR samples.
Figure 5.
Figure 5.
Size dependent sensitivity: (a) MWCNT sensors with dimensions (width × length) of 10 × 20 mm (A1, A2, A3); 10 × 10 mm (B1, B2, B3); and 10 × 5 mm (C1, C2, C3); (b) Graphite sensors with dimensions (width × length) of 10 × 20 mm (A1, A2, A3); 10 × 10 mm (B1, B2, B3); 10 × 5 mm (C1, C2); (c,d) Sensitivity versus strain curves for MWCNT and graphite sensors with dimensions of 10 × 20 mm (A), 10 × 10 mm (B), and 10 × 5 mm (C).
Figure 6.
Figure 6.
Multiple cycle tests: More than 400 cycles of period 3.04 s were carried out for the strain range of 150%–500%. (Inset image: the first 16 full cycles carried out over a time period of 48.6 s).
Figure 7.
Figure 7.
Linearization: response curves for graphite sensor with (blue) and without (black) a 2 MΩ parallel resistor.
See this image and copyright information in PMC

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