Facile Synthesis of Sprayed CNTs Layer-Embedded Stretchable Sensors with Controllable Sensitivity

Abstract

Flexible electronic devices have gained significant interest due to their different potential applications. Herein, we report highly flexible, stretchable, and sensitive sensors made of sprayed CNT layer, sandwiched between two polymer layers. A facile fabrication process was employed in which the CNT solution was directly sprayed onto a patterned bottom polymer layer, above which a second polymer layer was casted to get a sandwiched composite structure. Varying amounts of CNT solution (i.e., 10, 25, 40, 70, and 100 mL) were sprayed to get conductive CNT layers of different thicknesses/densities. The physical characteristics of the conductive CNT layers were studied through SEM and optical images. The starting electrical resistance values (without strain) as well as the changes in electrical resistance against human body motions were monitored. The synthesized samples exhibited good response against finger and wrist bending. The conductivity of the samples increased with increase of CNT solution volume while the sensitivity followed the inverse relation, suggesting that the sensors with controlled sensitivity could be fabricated for targeted strain ranges using the proposed method.

Electrical Stability and Piezoresistive Sensing Performance of High Strain-Range Ultra-Stretchable CNT-Embedded Sensors

“…However, it can be said that the C2 sensor exhibited a comparably stable sensing response, indicating that a CNT content of 2% is favorable for these sensors with various CNT contents. These test results can also be supported by the piezoresistive sensing mechanisms, which state that the composites with a CNTs amount in the percolation threshold range show higher sensitivity compared to the composites with CNTs contents outside of the percolation threshold range [ 11 ]. As a result, the small strain/stress applied to the CNT-embedded composites can significantly alter the CNTs conductive networks, leading to dramatic changes in electrical resistivity [ 11 ].…”

“…These test results can also be supported by the piezoresistive sensing mechanisms, which state that the composites with a CNTs amount in the percolation threshold range show higher sensitivity compared to the composites with CNTs contents outside of the percolation threshold range [ 11 ]. As a result, the small strain/stress applied to the CNT-embedded composites can significantly alter the CNTs conductive networks, leading to dramatic changes in electrical resistivity [ 11 ]. The electrical stability against varying voltages (shown in Figure 4 ) and resistance changes against varying strain amplitudes (shown in Figure 6 ) further endorse this fact.…”

“…Nevertheless, the dispersion of CNT particles homogeneously into the polymeric matrix is still a difficult task. Various dispersion methods, including spray-deposition [ 11 ], hot press [ 12 , 13 ], inkjet printing [ 14 ], three-roll milling [ 15 ], and ultra-sonication with dispersant [ 16 ], have been reported in the literature. Lipomi et al [ 17 ] sprayed a CNT solution on PDMS layers, serving as a conductive layer.…”

Mechanical Properties, Melting and Crystallization Behaviors, and Morphology of Carbon Nanotubes/Continuous Carbon Fiber Reinforced Polyethylene Terephthalate Composites

“…The results show that the sensor has high flexibility (100%), good resistance variation (160%), and repeatability (r 2 > 0.98). Khalid et al [ 19 ] prepared CNT polymer sandwich composites by spraying. The results show that this method is simple and efficient, CNT can be effectively dispersed, and CNT content can be controlled by controlling the concentration of CNT solution.…”

Highly Sensitive and Stretchable c-MWCNTs/PPy Embedded Multidirectional Strain Sensor Based on Double Elastic Fabric for Human Motion Detection

“…In recent years, flexible strain sensors have experienced rapid development and achieved a series of progresses in many fields like soft robotics [ 1 ], artificial skin [ 2 ], human motion detection [ 3 , 4 ], personal health monitoring [ 5 ], and human-machine interface [ 6 ]. To get better sensitivity and larger workable range, which are the main parameters of the strain sensor, many conductive materials based on semiconductors, nanomaterials, and conductive polymers were used to design strain sensitive sensors, such as ZnO [ 7 , 8 ], ZnSnO 3 [ 9 ], silver nanowire [ 10 ], silver nanoparticles [ 11 ], carbon nanotube [ 12 , 13 ], graphene [ 14 , 15 , 16 ], polypyrrole [ 17 ], and polyaniline [ 18 ], have been applied and coupled to stretchable substrates. These successfully prepared sensors can respond quickly to a large range of testing strain with high stretchability and sensitivity.…”