Researchers have designed a polymer of multi-walled carbon nanotubes (MWNTs), which when embedded in a polymer system can sense strain induced by voltage1. Such embedded nanotubes will have a wide range of applications in devising gas sensors, bio-molecular sensors, switch, solar cell, fuel cell and electro-mechanical sensors.
Carbon nanotubes (CNTs) can withstand large forces without forming defects. This property makes polymer-embedded CNTs very good candidates for improving mechanical properties. Nanotubes also exhibit a transition state from semiconducting to metallic when strain is applied. To exploit this, the researchers embedded MWNTs (having diameter of 25-40 nm) in epoxy polymer.
To control the conductivity of the polymer, carbon black nanoparticles were dispersed in epoxy polymer. The nanotubes were allowed to polymerize on a polycarbonate substrate giving rise to a thin channel shape, which was then bonded on a substrate of lead zirconate titanate, a piezoelectric substrate. Applying voltage, dynamic strain was generated in the piezoelectric substrate to which polymer nanobutes were bonded.
The nanotubes underwent a longitudinal and torsional deformation, and the polymer coating acted as both a mechanical constraint and also an interface resistive layer. The fabricated channel with even a very small percentage of nanotubes (0.57 per cent) was found to be extremely sensitive for dynamic strain sensing.
"This research significantly improves the understanding of physics at nano-scale," says lead researcher Debiprosad Roy Mahapatra from the department of aerospace engineering, Indian Institute of Science, Bangalore. The embedded polymer nanotubes will contribute to strain sensing in implants and wearable devices, safety monitoring of nuclear reactor structural elements, self-sensing parts of spacecrafts, and planetary exploration devices involving monitoring of strain.
