Buckypaper for high sensitivity strain and temperature sensing

Abstract

This study investigates the use of Carbon Nanotube (CNT) Buckypapers (BP) as strain and temperature sensors. To further improve the sensor sensitivity, the produced BP was subjected to a combination of post-treatments; namely, annealing, exposure to a boiling solvent, and compaction. The effect of these post-treatments on the sensor's gauge factor was evaluated to determine the best post-treatments (or combinations thereof) that give the highest gauge factor. Loading/unloading as well as heating/cooling experiments were carried out to examine the piezoresistivity behavior and temperature sensitivity of the produced sensors. The morphology of the best-performing sensor and its fracture morphology were evaluated using scanning electron microscopy (SEM) and compared to as-fabricated sensors that have not been subjected to any post-treatments. In addition, in-situ tensile testing of the BP sensor was carried out to elucidate the mechanisms which influence the response of the BP sensor under strain.

The study revealed that by employing a combination of annealing and compaction, it was possible to attain a remarkable sensitivity, with gauge factors exceeding 170 and a Temperature Coefficient of Resistance value of −0.0064 %/°C. It was observed that the sensor's electrical resistance increases with strain and decreases with temperature. The increase with strain was related to the effect of strain on the morphology of the dense entangled network of the CNTs that make up the BPs. The CNTs were observed to straighten and move away from each other thus reducing the CNT-CNT junctions responsible for electrical conductance. On the other hand, the decrease in electrical resistance as temperature increases is attributed to the increased inter-tube hopping of electrons which is facilitated by temperature. The CNT-based sensor with its high sensitivity, flexibility, and lightweight is suitable for a wide range of applications such as structural health monitoring, human motion sensing, wearable electronics, and biomedical applications.