A novel nickel nanostrand-silicone composite material at an optimized 15 vol% filler concentration demonstrates a dramatic piezoresistive effect with a negative gauge factor (ratio of percent change in resistivity to strain). The composite volume resistivity decreases in excess of three orders of magnitude at a 60% strain. The piezoresistivity does decrease slightly as a function of cycles, but not significantly as a function of time. The material's resistivity is also temperature dependent, once again with a negative dependence.
The evidence indicates that nickel strands are physically separated by matrix material even at high volume fractions, and points to a charge transport mechanism that causes a large change in conductivity for a small relative change in the distance between filler particles. Combined with the temperature dependence data, this suggests that conduction in this composite material may be dominated by quantum tunneling effects. Based upon a statistical model of junction character distribution, a quantum tunneling percolation model is applied that accurately reflects the mechanical and thermal trends.
