Elastomer Composites with a Tailored Interface Network toward Tunable Piezoresistivity: Effect of Elastomer Particle Size

Wearable strain sensors have significant potential applications for the development of the Internet of Things. As such, sensors based on conductive elastomer composites (CECs) for various sensing applications require different piezoresistive properties, i.e., strain sensitivity and sensing ranges. Herein, we report a facile strategy to fabricate thermoplastic polyurethane (TPU)/carbon nanostructure (CNS) composites designed for different applications based on different conductive interface network morphologies via forming the filler network at segregated TPU particles with various sizes. This strategy renders the composites tunable electrical conductivity (4 orders of magnitude change at low filler content) and mechanical and piezoresistive properties upon changing the TPU particle size. The larger the TPU particle size, the denser and stronger the conductive network, leading to higher electrical conductivity, better mechanical reinforcement, and more stable piezoresistive behavior. By contrast, using a smaller TPU particle size gives rise to relatively lower conductivity but higher elongation at break and much higher strain sensitivity. Composites with 0.7 wt % CNS using TPU particle sizes up to 212 μm have a gauge factor of 7668 at 300% tensile strain and elongation at break of 990%; whereas, when using TPU particles with 1000–1400 μm, the gauge factor is 175 for 300% tensile strain, and the elongation at break is 780%. These CEC composites have potential applications for a variety of flexible sensors.