Easy-Scalable Flexible Sensors Made of Carbon Nanotube-Doped Polydimethylsiloxane: Analysis of Manufacturing Conditions and Proof of Concept

Abstract

Carbon nanotube (CNT) reinforced polydimethylsiloxane (PDMS) easy-scalable sensors for human motion monitoring are proposed. First, the analysis of the dispersion procedure of nanoparticles into the polymer matrix shows that the ultrasonication (US) technique provides a higher electrical sensitivity in comparison to three-roll milling (3RM) due to the higher homogeneity of the CNT distribution induced by the cavitation forces. Furthermore, the gauge factor (GF) calculated from tensile tests decreases with increasing the CNT content, as the interparticle distance between CNTs is reduced and, thus, the contribution of the tunnelling mechanisms diminishes. Therefore, the optimum conditions were set at 0.4 CNT wt.% dispersed by US procedure, providing a GF of approximately 37 for large strains. The electrical response under cycling load was tested at 2, 5, and 10% strain level, indicating a high robustness of the developed sensors. Thus, this strain sensor is in a privileged position with respect to the state-of-the-art, considering all the characteristics that this type of sensor must accomplish: high GF, high flexibility, high reproducibility, easy manufacturing, and friendly operation. Finally, a proof-of-concept of human motion monitoring by placing a sensor for elbow and finger movements is carried out. The electrical resistance was found to increase, as expected, with the bending angle and it is totally recovered after stretching, indicating that there is no prevalent damage and highlighting the huge robustness and applicability of the proposed materials as wearable sensors.

Highly Flexible Strain Sensors Based on CNT-Reinforced Ecoflex Silicone Rubber for Wireless Facemask Breathing Monitoring via Bluetooth

“…In all cases, the current−voltage response was observed to be linear (Figure 2b), denoting ohmic behavior. Furthermore, the electrical conductivity values were in a similar range to those found in previous studies using other commercial silicone elastomers, 38 demonstrating the dispersion effectiveness of the three-roll-milling method.…”

“…In fact, the increase of both strength and stiffness is an indicator of a good distribution of CNTs . Moreover, the elongation at break slightly decreases with CNT content, but the values are well above those found for other flexible strain sensors. , …”

“…Figure shows the GF value and maximum working strain range of the developed nanocomposites compared to those of other carbon-based flexible strain sensors reported in the literature. The comparison is made with a wide range of flexible polymers (PDMS, Ecoflex, TPU, or IR) doped with carbon nanoparticles (CNT, CB, and graphene). ,,,– Most of these sensors cannot satisfy the requirements of a high GF and large strain range simultaneously, while nanocomposites obtained in this work stand out. As discussed above, the GF value of developed sensors consistently increases within the entire strain range, indicating that the conductive network is not completely disconnected, making it potentially useful for practical applications.…”

“…42 Moreover, the elongation at break slightly decreases with CNT content, but the values are well above those found for other flexible strain sensors. 19,38 Figure 5 shows the GF value and maximum working strain range of the developed nanocomposites compared to those of other carbon-based flexible strain sensors reported in the literature. The comparison is made with a wide range of flexible polymers (PDMS, Ecoflex, TPU, or IR) doped with carbon nanoparticles (CNT, CB, and graphene).…”

Strain Sensors Made of MXene, CNTs, and TPU/PSF Asymmetric Structure Films with Large Tensile Recovery and Applied in Human Health Monitoring

“…The sensors used in human body monitoring need to have good flexibility, wide sensing range, reasonable sensitivity, and high stability, and also have economic advantages such as low cost, microvolume, and easy formation. In the relevant reports so far, flexible strain sensors have been widely used, including resistive, − capacitive, , piezoelectric, , and triboelectric , sensors. Among them, the flexible resistance strain sensor presents the deformation generated by human motion in the form of resistance change and has become eye-catching to researchers.…”