Shear induced formation and destruction behavior of conductive networks in nickel/polyurethane composites during strain sensing

Stretchable sensors based on conductive polymer composites (CPCs) are attracting considerable interest from both academia and industry. For CPCs consist of elastomeric substrates with dispersed conductive fillers, a strain-induced conductivity-drop phenomenon (negative piezo-conductivity effect) is often observed in previous reported studies. Herein, CPCs with unconventional positive piezo-conductivity effect were prepared by employing a facile and low-cost fabrication process based on thermoplastic polyurethane (TPU) and conductive metal particles (nickel/iron particles). For the first time, a strongly stretch-induced conductive networks formation phenomenon was observed under tensile strain, contributing to the electrical resistivity of the composites decreases by more than 6 orders of magnitude under 20% tensile strain. The evolution of conductive networks and resistivity under uniaxial strain were studied with scanning electron microscope (SEM) and a modified mathematic model, respectively. Furthermore, these CPCs exhibits temperature sensing capability between 30 and 60 °C, indicating such method could be used to fabricate multi-functional sensors.