It is well known that a rubber material generally behaves as an electrical insulator and the vapor-grown carbon fiber (VGCF) has excellent electrical conductivity. In our study, we mixed carbon nanofiber (VGCF) into styrene-butadiene rubber, and investigated the relationship between strain and the electric capacitance of vulcanized rubber filled with VGCF, of which the hardness was not changed at all. The electric capacitance of the rubber filled with VGCF increased with the VGCF content, but decreased with the increasing tensile strain. It was confirmed that change rate of the electric capacitance is related to the VGCF contents of the fillers. In order to investigate the relationship between strain and electric capacitance of rubber with VGCF, the rubber composites filled with VGCF is feasible to apply as a strain sensor.
