Flexible strain sensors with high sensitivity and large working range prepared from biaxially stretched carbon nanotubes/polyolefin elastomer nanocomposites

Abstract

Flexible strain sensors are a new generation of flexible and stretchable electronic devices that attracted increasing attention due to their practical applications in many fields. However, maintaining a wide detectable strain range while improving the sensitivity of flexible strain sensors remains challenging. In this study, flexible strain sensors with a large working range based on biaxially stretched carbon nanotubes (CNTs)/polyolefin elastomer (POE) nanocomposites were fabricated. Biaxial stretching was demonstrated to enhance the uniform dispersion and orientation of CNTs, thereby improving the performance of sensors. The optimal stretching ratios (SRs) of nanocomposites were investigated and the data revealed an increment in the sensitivity of sensors with SRs, while the working range first increased after biaxial stretching and decreased at higher SRs. Compared to the 9 wt% CNT/POE‐1.0 sensor with a gauge factor (GF) value of 2.37 and a detectable range of 0.5%–230%, the CNT/POE‐2.0 sensor exhibited an enhanced sensitivity (GF = 3935.12) coupled with a wider detectable range (0.5%–710%) and better stability. Besides, CNT/POE‐2.0 sensor also achieved the monitoring of head movements, mouth opening, facial expression, and physiological signals, showing a potential for use in wearable electronic products.

Flexible strain sensors with high sensitivity and large monitoring range prepared by biaxially stretching conductive polymer composites with a bilayer structure

“…This further demonstrated that biaxial stretching could improve the secondary dispersion of the CNTs in the POE polymer, thus improving the sensitivity of strain sensors. 23,36 Compared with recently reported sensors, 9,10,12,21,23,[37][38][39][40][41] CNT/POE-POE strain sensors show greater advantages in sensitivity and monitoring range, which provides a good way to meet the requirements of a wider monitoring range and higher sensitivity (see Figure 8c).…”

“…A DC digital source meter (Tektronix PWS4323) was used to provide power and the current was collected at a fixed voltage of 3 V through a picoampere-meter (Keithley 6485). The conductivity of nanocomposites was calculated by Equation 1 21 :…”

“…32 After biaxial stretching, the F value of the nanocomposite increases to 0.1469, indicating that the orientation of nanofiller within POE is gradually normalized, which also indicates that biaxial stretching can effectively promote the orientation arrangement of CNTs in the stretching plane. 21,23,32 According to the XRD pattern shown in Figure 7, the neat POE polymer has an obvious diffraction peak at 21.52 . 21 Compared with neat POE, the intensity and width of the diffraction peak of CNT/POE-POE nanocomposites were changed.…”

“…21,23,32 According to the XRD pattern shown in Figure 7, the neat POE polymer has an obvious diffraction peak at 21.52 . 21 Compared with neat POE, the intensity and width of the diffraction peak of CNT/POE-POE nanocomposites were changed. The peak intensity was increased and the peak width was enlarged, indicating that the crystallinity increased.…”

“…Biaxial stretching is a simple and effective method for preparing flexible strain sensors by improving the dispersion and orientation of nanofillers. Based on our previous research, 21 a 8 wt% CNT/polyolefin elastomer (POE) flexible strain sensor was prepared through biaxial stretching. The CNT/POE sensor of stretching ratio (SR) = 2.0 exhibited high sensitivity (GF = 3935.12) and a wide detection range (0%–710%).…”