Development of a novel strain sensor based on fluorocarbon-elastomeric nanocomposites: Effect of network density on the electromechanical properties

A fluorocarbon elastomer (FCE)/nanocarbon black (NCB) nanocomposites based strain sensor was developed and the effect of network density on the AC and DC conductivity as well as on the electromechanical performance of the sensor was investigated. Nanocomposite matrices with different network densities were achieved by irradiating with high energy radiation from Co-60 gamma source for different doses. The nanocomposite having 0.1 weight fraction of NCB showed frequency-dependent increase in the AC conductivity (σAC) over the entire frequency range (100 Hz to 1 MHz); whereas nanocomposite having 0.2 and 0.3 weight fractions showed no significant frequency dependence. Interestingly at 0.35 weight fraction, conductor to insulator transition took place at 0.01 MHz, and a conductivity plateau was observed in 100 Hz to 0.01 MHz range. Network density was found to have a profound effect on the sensing range as well as on the gauge factor. Cyclic strain sensing response was also found to be affected by network density and the best results were observed for a network density of 73.2 μmol/g. At higher network density (290 μmol/g), two peaks were observed for each strain cycle and the sensing response was not stable. For 5 and 10% cyclic strains, gauge factor was around 14 and no change in gauge factor was observed within 2-5 mm/min strain rates.