Pre-Strain Stimulation of Electro-Mechanical Sensitivity of Carbon Nanotube Network/Polyurethane Composites

The change of electrical resistance of a highly extensible composite sensors consisting of a network of entangled multi-wall carbon nanotubes (CNTs) and thermoplastic polyurethane elastomer in the course of elongation was stimulated by initial tensile deformation. Though the initial deformation irreversibly changes the arrangement of CNT network, subsequent cyclic elongation and corresponding resistance change is stable. The resistance sensitivity, quantified by a gauge factor, which defines the sensitivity of strain sensor as the relative resistance change divided by the applied strain, increases nearly five times from the value of about five for not initially elongated composites. This is a substantial increase, which ranks the composites among materials with the highest electromechanical sensitivity. The observed sensitivity increase is discussed on basis of the cracking of a nanotube network with extension when the number of contacts between nanotubes decreases and thus the network has fewer interconnections that can carry an electric current.