Strain-Sensing Elastomer/Carbon Nanofiber Metacomposites

Electrically conductive elastomer nanocomposites reinforced with 1, 2, 3, and 5 wt % carbon nanofibers (CNFs) have been fabricated from two slightly different elastomers (VM1, VM2). The electrical and dielectric percolation threshold of 1 wt % in VM2 nanocomposites is much lower than 3 wt % in the VM1 nanocomposites. Unique negative permittivity is observed in the composites with the CNF concentration correlating well with the percolation thresholds. About 40% unrecoverable strain loss and a permanently increased resistivity by about 2 orders of magnitude are observed due to the formation and opening/closing of the cracks during the first cyclic loading. In the subsequent stretching cycles, the reversible resistivity at 120% strain is about 2-3 orders of magnitude higher than that at 40% strain. Higher fraction of ethylene is found to reduce the thermal stability of the propylene portion in the elastomer. An enhanced thermal stability of the elastomers is observed in both nanocomposite systems; however, the CNFs affect the glass transition and melting behaviors in an opposite way in the two different nanocomposite systems arising from the dispersion quality difference. Melting enthalpy from differential scanning calorimetry (DSC) reveals that the CNFs play a more important role in the VM2 crystallization than that in VM1 composites.