A highly stretchable natural rubber/buckypaper/natural rubber (NR/N-BP/NR) sandwich strain sensor with ultrahigh sensitivity

Flexible strain sensors have received intensive attention owing to their wide application prospects in the fields of wearable, personal electronics, and intelligent robotic systems. But it is a huge challenge for them to possess high sensitivity, fast response, wide sensing range, and superior durability synergistically. In order to solve these issues, we prepared a new type of buckypaper with excellent mechanical properties (elongation at break of about 22%) and electrical conductivity (33 S/cm) by filtering carbon nanotube (CNT) aqueous dispersion mixed with a small amount of natural rubber latex (NR), named natural rubber-buckypaper (N-BP). By taking advantage of the robust N-BP, an NR/N-BP/NR strain sensor was creatively constructed by sandwiching the N-BP with two NR layers using the casting-curing method. The NR/N-BP/NR sandwich strain sensor showed a very high gauge factor value (2280), ultrashort response time (21 ms), very large sensing range (500%), and satisfactory sensing stability (2000 cycles at 100% strain). As for practical application, this NR/N-BP/NR strain sensor could accurately capture large or subtle human body movements, such as limb joint movements and facial movements, and could even distinguish the pronunciation of different English words. As a whole, the NR/N-BP/NR sandwich strain sensor exhibited promising applications in wearable electronics. The NR/N-BP/NR sandwich strain sensor with wide working range and high sensitivity based on the excellent performance of N-BP.