Testing and characterization of carbon nanotubes as strain sensors

Abstract

The potential of using carbon nanotube coated flexible cloth as strain gauges was studied. Samples were prepared by sonicating strips of cloth inside a 1mg/ml carbon nanotube in propylene carbonate solution. A dynamic mechanical analyzer was built that applied uniaxial cyclical strains to the samples and recorded the force and strain applied. The DMA also provided a constant voltage to the samples while recording the resistance response of the strain gauges. The samples were tested using the dynamic mechanical analyzer for their response to variables such as strain and time. The samples were successfully tested at strains ranging from 1% to 50%. The conductivity of the samples was measured. We studied the effects that a carboxylate and the sulfonate functional groups of the carbon nanotubes have on the strain sensors, the effect of the sonication time, and the effect that leaving the strain sensors inside the solution for different amount of times has on the strain sensors. It was discovered that the samples dried overtime, thus decreasing the conductivity of the samples and damaging the strain sensors. An encapsulation method was developed and studied to counter the drying effect. The results showed that the encapsulation method did delay the decaying of the samples. Moreover, it was concluded that the sulfonate group had higher changes in resistance than the carboxylate group. While increased sonication time did not seem to have a measurable effect on the resistance of the sulfonate CNT samples, this was not true for the carboxylate group CNTs. The carboxylate group CNTs seemed to have a higher initial resistance with longer sonication time and a lower resistance with increasing time sitting in the solution. Overall, it was concluded that carbon nanotubes have a promising potential as macro level strain sensors for high-elongation applications but more development is yet to be done.