Towards tunable resistivity-strain behavior through construction of oriented and selectively distributed conductive networks in conductive polymer composites

The resistivity-strain behavior of conductive polymer composites (CPCs) has gained intense interest due to its importance for various applications. The resistivity of CPCs often increases substantially and linearly under strain. To achieve constant resistivity under strain, a large filler content and special network configuration are often required. And a tunable step-wise resistivity-strain behavior has yet to be reported. Herein, a new method combining polymer blends and pre-stretching is introduced to modify the resistivity-strain behavior of CPCs based on thermoplastic polyurethane (TPU)/polyolefin elastomer (POE) with multi-walled carbon nanotubes (MWCNTs) selectively incorporated in the TPU phase. Depending on the compositions of blends and the intensity of pre-stretching, various interesting resistivity-strain behaviors have been achieved. The resistivity can be either linearly increasing or constant. Interestingly, two-stepwise resistivity-strain behavior has been achieved, with first an increase then a constant value. To understand this unique phenomenon, the phase morphology and conductive network structure are systematically characterized. It is observed that the orientation of MWCNTs is strongly correlated with overall resistivity. Finally, a mechanism involving fibrillization and "slippage" between conductive phases is proposed to explain the resistivity-strain dependency. This study provides guidelines for the preparation of high performance strain sensors as well as stretchable conductors.