Electrical Resistance Change under Strain of CNF/Flexible-Epoxy Composite

Abstract

Carbon nanofibers (CNFs) have good electrical conductivity. Addition of a few percent of carbon nanofibers to polymers yields electrical conductivity but hardly affects the mechanical properties of the polymers. These conductive polymers may be useful for sensing applications, such as strain sensors and chem-resist sensors. Many researchers have reported on the electrical conductivity, but the electrical resistance change under strain, i.e. piezoresistivity, of the carbon nanofiber filled resin has not been fully investigated. In this study, the electrical resistance change under strain of CNF/flexible-epoxy composites was investigated experimentally and analytically. Experimental results show that the electrical resistance change under strain is non-linear and much larger than that in metal, and the sensitivity of the electrical resistance change to strain decreases as the weight fraction of CNF increases. The mechanism of the electrical resistance change under strain of CNF/polymer composites was discussed by using electrical circuit simulation based on a percolation network model and tunneling effect between CNFs. The results imply that the non-linear behavior is caused by tunneling resistance change between CNFs, and that the decrease of sensitivity with increasing weight fraction of CNF is caused by the nature of the percolation network.