Ultra-stretchable, sensitive and durable strain sensors based on polydopamine encapsulated carbon nanotubes/elastic bands

High-performance flexible and wearable strain sensors for human motion detection have been widely investigated recently. Here, we report a flexible strain sensor with ultra-high stretchability, large sensitivity and excellent durability based on common elastic bands from every day life. The strain sensor was fabricated by embedding carbon nanotubes (CNTs) into elastic bands (EB) through swelling-ultrasonication treatment. It is found that the CNTs with a large aspect ratio migrated into the inner regions of the EB successfully, generating a conductive CNT/EB shell with a thickness of about 30 μm. The CNT/EB bands were then coated with a polydopamine (PDA) layer by self-polymerization of dopamine to stabilize the sensitive regions. Interestingly, the specific strength and specific elongation of PDA/CNT/EB are enhanced by about 55% and 23% respectively after the coating of PDA, compared to the pure EB. Strain sensing tests indicated that our strain sensors had desirable integration of an ultra-high sensing range (920% strain), large sensitivity (a gauge factor (GF) of 129 under a strain of 780–920%), superior stability (10 000 cycles at 100% strain) and a fast response speed. Additionally, there was a direct correlation between the mechanical hysteresis HM value and the weak shoulder peak. The sensing mechanism of the strain sensors were investigated. Monitoring of human body motions (such as finger bending, muscle movements and knee-joint movements) indicates that our stretchable PDA/CNT/EB sensor has broad application prospects for human-machine interfaces in the artificial intelligence (AI) field.